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A small black star
floats through space.
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This is the Sun, billions of
years in the future.
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00:00:10,910 --> 00:00:13,843
It's all that remains
of our solar system,
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00:00:15,010 --> 00:00:18,586
the sole survivor of
a dramatic history
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00:00:18,610 --> 00:00:21,510
of elegant beauty
and extreme violence.
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00:00:23,610 --> 00:00:26,043
Just because things look
really nice and serene
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00:00:26,109 --> 00:00:28,510
now doesn't mean
it's always been that way.
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00:00:30,309 --> 00:00:33,143
There are a lot of planets
that could have made it
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00:00:33,209 --> 00:00:35,910
but didn't,
and we just happen to be
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one of the lucky ones that did.
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00:00:38,943 --> 00:00:41,143
The players in
our solar system's story
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00:00:41,209 --> 00:00:44,386
are more tangled up
than we ever imagined.
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The more we look at this stuff,
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00:00:46,410 --> 00:00:48,986
the more we realize that
everything affects everything
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00:00:49,010 --> 00:00:50,643
else, including us.
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00:00:50,710 --> 00:00:54,443
How did we go from
a vibrant family of planets
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orbiting the yellow sun
to a lone,
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00:00:57,209 --> 00:00:59,209
dead zombie star?
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It's an old familiar story.
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A bunch of planets orbit
a yellow star
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in a quiet suburb of
the Milky Way galaxy.
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But it's not the whole story.
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Over the past decade,
our vision of
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our solar system has been
completely revamped.
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Think of the solar system as
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an old-fashioned mafia
crime family.
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The sun is the Don,
his quarreling children,
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the planets.
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Their story,
like any good mob movie,
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is an epic tale of empire
building,
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sibling rivalry, greed,
and ultra violence.
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00:02:00,610 --> 00:02:02,686
The origin of
the solar system was chaotic
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00:02:02,710 --> 00:02:05,386
and violent...
Planets colliding,
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00:02:05,410 --> 00:02:08,643
planets even changing places.
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00:02:08,710 --> 00:02:12,185
Now, a shift
in our understanding reveals
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00:02:12,209 --> 00:02:17,510
a tale of tangled alliances
between family members.
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00:02:17,610 --> 00:02:19,443
Just think about
how much our view
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00:02:19,510 --> 00:02:21,209
of the solar system has changed.
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00:02:21,309 --> 00:02:23,986
The planets used to be
so far away from each other,
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00:02:24,010 --> 00:02:26,019
and of course, they had nothing
to do with each other.
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00:02:26,043 --> 00:02:28,786
And now, the history is all
about the interaction.
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00:02:28,810 --> 00:02:31,586
So the idea that everything
is just
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00:02:31,610 --> 00:02:35,343
its own world and doesn't
interact is completely wrong.
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00:02:35,410 --> 00:02:37,710
We like to think of astronomy
as looking up,
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looking outward,
away from ourselves.
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00:02:40,309 --> 00:02:42,743
But the more we do that,
the more we realize how
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00:02:42,810 --> 00:02:45,610
connected we are
to everything out there.
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00:02:45,710 --> 00:02:48,686
You probably have some
material in your body from
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00:02:48,710 --> 00:02:50,043
pretty much every world that
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00:02:50,109 --> 00:02:52,085
ever existed
in the solar system.
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00:02:52,109 --> 00:02:54,610
Like any good mobster movie,
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00:02:54,710 --> 00:02:58,986
our story starts with the humble
rise of the Godfather.
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00:02:59,010 --> 00:03:02,043
In this tale,
that's the birth of the Sun.
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00:03:03,410 --> 00:03:06,810
But exactly how that happens
is a mystery.
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00:03:08,209 --> 00:03:10,910
When we're trying to figure out
how the solar system began,
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00:03:11,010 --> 00:03:12,586
you know, we don't have
a time machine.
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00:03:12,610 --> 00:03:17,143
So what can we use to find out
about how it formed?
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The solar system has the answer,
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00:03:22,209 --> 00:03:25,510
its own time machines...
Meteorites.
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00:03:30,410 --> 00:03:32,410
Meteorites are pieces of
the solar system from
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00:03:32,510 --> 00:03:35,510
the distant past, and they've
remained unchanged since then.
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So they're like little
time capsules.
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They're like fossils from before
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00:03:43,410 --> 00:03:45,043
our solar system even formed.
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By studying them,
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00:03:46,343 --> 00:03:48,810
we can really study what was
happening and what was going
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00:03:48,910 --> 00:03:51,810
on in the very early days of
our own solar system.
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00:03:54,710 --> 00:03:56,610
2020...
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Scientists study ancient
material trapped inside
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a meteorite found in
Murchison, Australia.
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00:04:04,309 --> 00:04:07,986
The Murchison meteorite
contains tiny crystals called
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presolar grains
that predate our sun.
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And trapped
within them is evidence of
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00:04:18,209 --> 00:04:20,643
the history of the formation
of our solar system.
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00:04:22,143 --> 00:04:23,886
The presolar grains
are made up of
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00:04:23,910 --> 00:04:28,643
elements like silicon that
form inside giant stars.
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When these stars die,
they blow out
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00:04:35,610 --> 00:04:39,185
huge clouds of gas
and grains of dust.
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00:04:39,209 --> 00:04:42,743
The term presolar grain
doesn't sound very romantic,
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but actually,
we might call those stardust,
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because these materials
are things that were
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made in stars
that no longer exist.
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The Murchison meteorite
contains grains
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from at least
46 different stars.
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What the Murchison
meteorite tells us is that
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00:05:01,043 --> 00:05:03,043
the material that came together
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00:05:03,143 --> 00:05:06,986
that formed our solar system
had its origination in
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00:05:07,010 --> 00:05:09,085
dozens of different stars.
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00:05:09,109 --> 00:05:13,643
These stars died and blew out
all of these materials.
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00:05:13,710 --> 00:05:16,943
And then created this huge
cloud of gas and dust
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00:05:17,043 --> 00:05:18,109
called a nebula.
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00:05:19,143 --> 00:05:21,085
The sources of
the material in that cloud
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could come from one of
a number of places.
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The material from lots of stars'
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atmospheres
could be mixed in there.
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In the mix were
the ingredients to build
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the solar system,
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00:05:33,510 --> 00:05:35,410
but we don't know what triggered
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the gas and dust
to form the Sun.
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A 2020 study
may have the answer.
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00:05:44,109 --> 00:05:45,810
One of the coolest
things we've discovered
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in the last couple of decades
about the Milky Way
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is there's a giant stream
of stars that's
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stretching across virtually
the whole sky.
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These stars were not
born in the galaxy.
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They're not from here.
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00:06:02,143 --> 00:06:03,543
If not from our galaxy,
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00:06:03,610 --> 00:06:05,710
then from where?
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00:06:06,743 --> 00:06:10,243
We think these stars actually
came from
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00:06:10,309 --> 00:06:14,209
the Sagittarius Dwarf galaxy,
which orbits the Milky Way.
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Over five billion years ago,
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00:06:18,309 --> 00:06:21,443
the Sagittarius Dwarf
galaxy wanders
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too close to the Milky Way.
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Our galaxy's powerful gravity
drags Sagittarius towards it.
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The galaxies collide.
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As this is happening,
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the Milky Way is tearing
Sagittarius apart,
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ripping stars out of it.
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This is truly intergalactic
cosmological drama at play.
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00:06:48,109 --> 00:06:51,185
This collision shakes up
the Milky Way.
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When a body passes
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00:06:54,209 --> 00:06:56,410
through the disc
of our galaxy, it's
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00:06:56,510 --> 00:06:58,786
gonna set off ripples,
and that's going to compress
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00:06:58,810 --> 00:07:02,510
the gas clouds, and that's gonna
create star formation.
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00:07:02,610 --> 00:07:06,185
The Sagittarius Dwarf smashing
into the Milky Way
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00:07:06,209 --> 00:07:09,810
is like dropping a boulder
into a pond.
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00:07:15,743 --> 00:07:18,610
It sets out ripples of density,
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00:07:18,710 --> 00:07:21,543
and it disturbs
everything in the galaxy,
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00:07:21,610 --> 00:07:23,986
but it doesn't disturb
everything equally.
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It causes some clumps of dust
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and gas to start
accumulating together.
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00:07:33,143 --> 00:07:36,586
The disruption in
one galactic zip code leads
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00:07:36,610 --> 00:07:39,743
to new activity in others
across the Milky Way.
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The ripples trigger gas
and dust left over
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from the dying stars
to split into clumps,
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sparking a frenzy of
star formation.
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Look, if you were an observer,
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00:07:54,010 --> 00:07:57,085
suddenly, out of
these little clumps of gas
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00:07:57,109 --> 00:08:00,209
come bright ignition sparks
all at once.
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00:08:04,943 --> 00:08:07,043
If you were to stand there
long enough,
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00:08:07,109 --> 00:08:08,710
watching this stellar nursery,
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00:08:08,810 --> 00:08:11,043
it might look kind of like
a field at night
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00:08:11,109 --> 00:08:13,143
with fireflies blinking on.
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00:08:14,643 --> 00:08:17,810
Perhaps the Sun formed in
this starburst.
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The passage
of the Sagittarius Dwarf
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through our galaxy correlates
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00:08:23,610 --> 00:08:26,486
in time to the formation and
birth of our sun.
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00:08:26,510 --> 00:08:31,386
So maybe our solar system came
about as a result of
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the Sagittarius Dwarf passing
through our galaxy
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over five million years ago.
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Of course, we don't know for
sure if this is what triggered
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00:08:39,510 --> 00:08:42,510
the formation of our sun,
but the timing does fit.
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4.6 billion years ago,
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part of the cloud seeded with
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00:08:50,610 --> 00:08:54,743
material from dying stars
grows denser,
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until it gets so massive,
it collapses.
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As the gas cloud collapses,
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00:09:03,109 --> 00:09:07,285
it gets hotter and hotter
and spins faster and faster,
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00:09:07,309 --> 00:09:10,443
forming a dense core
at its center.
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The core is the protostar
that will later become our sun.
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The protostar drags in
more and more gas and dust,
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creating a region of materials
spinning around it
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called the protoplanetary disk.
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As the Sun builds up more mass,
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it's getting compressed
gravitationally, and so the core
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is getting hotter
and hotter and hotter.
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The densities are increasing.
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The new Don, the head
of our solar mobster family,
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immediately reveals
a ferocious nature,
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blasting out supercharged jets
of radiation.
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The early sun was not
the calm, glowing orb
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that we see in our sky today...
It was far more chaotic.
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It's sort of like
in its toddler phase.
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It was acting up all the time.
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It has all of this energy that
pushes material off of
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the surface and launches it into
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what we call the solar wind.
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The blizzard of
particles races out
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at over a million miles an hour.
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It smashes into
the protoplanetary disk
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and blows the gas away.
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At the same time, the Sun's
core heats up to 18 million
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degrees Fahrenheit,
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triggering the fusion of
hydrogen into helium.
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And that releases
a tremendous amount of
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energy that eventually works
its way back to the surface of
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the star and comes out as light.
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Finally, the Sun
becomes the recognizable
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sun that we see
in our sky today.
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The sun is now the Godfather,
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pulling the strings on
the solar system.
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00:11:04,610 --> 00:11:06,810
The young Don's rise to the top
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00:11:06,910 --> 00:11:09,986
triggers a power struggle
with its willful children,
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the planets.
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It's a brutal fight
for survival.
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4.6 billion years ago,
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00:11:30,410 --> 00:11:34,743
our mob family rises in
a quiet suburb of the Milky Way.
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00:11:35,810 --> 00:11:39,810
Its Godfather, the Sun,
forms from a collapsed
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stellar nebula.
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The greedy star scarfs down
most of the cloud of gas
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00:11:48,309 --> 00:11:50,243
and dust, but just enough
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00:11:50,309 --> 00:11:53,209
is left over
to build the planets.
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00:11:53,309 --> 00:11:56,610
We're standing here on a big
planet, and we look up in
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the sky, and we see other
planets going around the Sun,
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00:11:59,010 --> 00:12:02,285
and it's an obvious
and challenging question to ask,
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00:12:02,309 --> 00:12:03,810
where did these planets
come from?
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00:12:05,743 --> 00:12:09,410
How did the leftover gas
and dust build the planets?
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00:12:10,943 --> 00:12:13,786
To solve the mystery,
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00:12:13,810 --> 00:12:16,143
scientists study
other star systems
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across the Milky Way.
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00:12:18,410 --> 00:12:19,886
We can't go back in time
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00:12:19,910 --> 00:12:22,085
and watch our own
solar system forming.
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00:12:22,109 --> 00:12:25,610
But we can look at other,
new solar systems as they're
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00:12:25,710 --> 00:12:28,843
forming and use that to
understand how our own
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00:12:28,910 --> 00:12:30,143
might have formed.
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00:12:34,043 --> 00:12:40,943
Star system PDS 70
is one such system.
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00:12:41,043 --> 00:12:44,943
It's young,
just 5.4 million years old.
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00:12:47,309 --> 00:12:50,643
And nestled inside
the protoplanetary disk are
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00:12:50,710 --> 00:12:54,843
two infant planets
feeding on gas and dust.
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00:12:58,043 --> 00:13:00,986
We can see these baby
exoplanets pulling in
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00:13:01,010 --> 00:13:03,610
material and creating
these gaps in the disk.
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00:13:03,710 --> 00:13:05,910
It's an amazing discovery...
It's kind of mind-blowing
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00:13:06,010 --> 00:13:09,710
that we can see a new
solar system being born.
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00:13:11,643 --> 00:13:14,309
These snapshots,
these systems like PDS 70,
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00:13:14,410 --> 00:13:17,986
are so valuable, because they
let us test our theories.
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00:13:18,010 --> 00:13:21,043
We thought planets formed from
these discs of dust and gas,
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00:13:21,143 --> 00:13:23,543
but we hadn't seen it until now.
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00:13:23,610 --> 00:13:25,810
What we couldn't see was how gas
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00:13:25,910 --> 00:13:29,243
and dust bind together
to grow into planets.
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00:13:35,610 --> 00:13:37,185
That took an astronaut on
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00:13:37,209 --> 00:13:40,410
the space station messing
around with breakfast.
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00:13:42,810 --> 00:13:44,243
Ah.
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00:13:44,309 --> 00:13:45,586
Don Pettit, this one astronaut,
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00:13:45,610 --> 00:13:47,810
took a bag
full of salt and sugar
235
00:13:47,910 --> 00:13:50,085
and coffee grounds and just
shook it to see what would
236
00:13:50,109 --> 00:13:51,943
happen in 0G.
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00:13:52,043 --> 00:13:53,643
And to his astonishment,
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00:13:53,710 --> 00:13:57,486
he saw that they immediately
clumped up.
239
00:13:57,510 --> 00:14:01,243
It's effectively electrostatic
forces that are causing
240
00:14:01,309 --> 00:14:03,443
those clumps to form...
The salt grains
241
00:14:03,510 --> 00:14:05,886
rub around with each other,
and they develop a charge,
242
00:14:05,910 --> 00:14:07,543
an electrical charge.
243
00:14:07,610 --> 00:14:10,410
And so those clumps
very naturally form.
244
00:14:12,143 --> 00:14:14,686
These clumps were strong.
245
00:14:14,710 --> 00:14:19,386
They didn't fall apart when
they hit the sides of the bag.
246
00:14:19,410 --> 00:14:21,610
And sitting down on the ground,
247
00:14:21,710 --> 00:14:24,643
down at mission control,
was astronaut Stan Love,
248
00:14:24,710 --> 00:14:26,743
going, "Oh, my God,
Don, you've solved the first
249
00:14:26,810 --> 00:14:28,610
steps of planetary formation."
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00:14:30,309 --> 00:14:34,143
A very similar process went on
251
00:14:34,209 --> 00:14:36,309
in the early
protoplanetary disk.
252
00:14:36,410 --> 00:14:38,610
Instead of salt,
it's mineral grains.
253
00:14:42,610 --> 00:14:46,643
So the dust grains that you
start with stick to each other
254
00:14:46,710 --> 00:14:48,410
because of electrostatic forces,
255
00:14:48,510 --> 00:14:49,710
basically static cling,
256
00:14:49,810 --> 00:14:51,843
and it's almost exactly
identical to how
257
00:14:51,910 --> 00:14:54,143
a dust bunny forms in your room.
258
00:14:54,209 --> 00:14:56,810
These are cosmic dust
bunnies that
259
00:14:56,910 --> 00:15:01,386
will some day grow up
into giant planets.
260
00:15:01,410 --> 00:15:06,143
Astronomers call these
cosmic dust bunnies pebbles.
261
00:15:08,043 --> 00:15:11,743
We think clumping dust
particles formed trillions
262
00:15:11,810 --> 00:15:15,085
of pebbles each around
an inch in diameter.
263
00:15:15,109 --> 00:15:18,686
It's the first step in
planet construction.
264
00:15:18,710 --> 00:15:20,986
The next step in
forming a planet
265
00:15:21,010 --> 00:15:23,543
involves planetesimals
and these are objects that are
266
00:15:23,610 --> 00:15:26,643
roughly half a mile
to 100 miles in size.
267
00:15:28,743 --> 00:15:31,610
But how pebbles build
planetesimals was
268
00:15:31,710 --> 00:15:36,109
a mystery, because pebbles
don't play well together.
269
00:15:38,309 --> 00:15:40,185
Grains of protoplanetary
material stick
270
00:15:40,209 --> 00:15:42,085
together because
of static charge.
271
00:15:42,109 --> 00:15:44,143
The problem is,
once they get too big,
272
00:15:44,209 --> 00:15:46,085
that force isn't enough,
and they'll just
273
00:15:46,109 --> 00:15:47,610
bounce off each other.
274
00:15:53,710 --> 00:15:57,043
Yet we know that we have to
get all the way up to hundreds
275
00:15:57,109 --> 00:15:58,886
of miles across to build
our planetesimals.
276
00:15:58,910 --> 00:16:02,610
How do you build a bigger
structure when the particles
277
00:16:02,710 --> 00:16:04,185
that you're trying
to lump together
278
00:16:04,209 --> 00:16:05,710
are bouncing off of each other?
279
00:16:07,343 --> 00:16:10,486
So a new idea
came forward about how to make
280
00:16:10,510 --> 00:16:12,710
this big jump from
pebble-sized things
281
00:16:12,810 --> 00:16:14,610
all the way up to planetesimals,
282
00:16:14,710 --> 00:16:17,143
and this relies on
the interaction of a huge number
283
00:16:17,209 --> 00:16:19,643
of pebbles moving together
through the gas
284
00:16:19,710 --> 00:16:21,586
around the star.
285
00:16:21,610 --> 00:16:25,309
In the disk
of gas and dust that encircles
286
00:16:25,410 --> 00:16:26,519
the young sun,
287
00:16:26,543 --> 00:16:30,843
pebbles will begin to coalesce
into these big clouds,
288
00:16:30,910 --> 00:16:35,743
much in the same way that
individual fish will form
289
00:16:35,810 --> 00:16:36,943
schools of fish.
290
00:16:37,043 --> 00:16:41,486
More and more pebbles
join the cloud.
291
00:16:41,510 --> 00:16:44,243
Eventually,
you get enough of them
292
00:16:44,309 --> 00:16:46,843
together that they collapse
under their own gravity
293
00:16:46,910 --> 00:16:48,243
and make one big planetesimal.
294
00:16:59,710 --> 00:17:01,743
The planetesimals face a race
295
00:17:01,810 --> 00:17:05,586
against time to grow
into planets.
296
00:17:05,610 --> 00:17:07,610
They must grab enough
building material
297
00:17:07,710 --> 00:17:11,309
from the protoplanetary disk
before their Don,
298
00:17:11,410 --> 00:17:13,910
the Sun, blasts it all away.
299
00:17:26,209 --> 00:17:28,510
4.6 billion years ago,
300
00:17:28,610 --> 00:17:32,185
a fierce battle erupts between
the head of the family,
301
00:17:32,209 --> 00:17:35,143
the Sun, and his children,
the growing planets.
302
00:17:35,209 --> 00:17:40,410
The Godfather is armed and
dangerous and threatening to
303
00:17:40,510 --> 00:17:42,910
destroy the planet's food source
304
00:17:43,010 --> 00:17:45,610
with his weapon of choice,
the solar wind.
305
00:17:46,610 --> 00:17:49,386
There's this strong wind
of high-energy particles
306
00:17:49,410 --> 00:17:51,043
coming out of the Sun.
307
00:17:51,109 --> 00:17:53,309
That blows away the disk of gas.
308
00:17:54,910 --> 00:17:57,443
The planets must fight
to grab hold of
309
00:17:57,510 --> 00:18:01,243
the remaining resources before
the Sun drives them away.
310
00:18:01,309 --> 00:18:06,743
So it's a race against time...
Jupiter is racing
311
00:18:06,810 --> 00:18:09,243
the Sun to capture
as much material as
312
00:18:09,309 --> 00:18:12,243
it can before the Sun
blows it all away.
313
00:18:12,309 --> 00:18:15,343
And what we see from studying
other solar systems is
314
00:18:15,410 --> 00:18:19,209
that those disks only last for
about five million years.
315
00:18:19,309 --> 00:18:21,343
We used to think
of the solar system's
316
00:18:21,410 --> 00:18:24,410
protoplanetary disk
like an old-school diner
317
00:18:24,510 --> 00:18:27,143
where the mob family
came to eat.
318
00:18:27,209 --> 00:18:31,185
The firstborn child, Jupiter,
grows by wolfing down
319
00:18:31,209 --> 00:18:34,510
planetesimals, followed by
a second course of gas.
320
00:18:35,710 --> 00:18:38,686
The old model of planet
formation is the idea that
321
00:18:38,710 --> 00:18:42,743
these large-ish planetesimals
that are miles across
322
00:18:42,810 --> 00:18:44,143
collide and stick to each other,
323
00:18:44,209 --> 00:18:46,486
kind of like modeling clay,
until you get a bigger
324
00:18:46,510 --> 00:18:47,743
and bigger object that can
325
00:18:47,810 --> 00:18:50,686
eventually get so massive that
it starts to then pull in
326
00:18:50,710 --> 00:18:55,443
the more diffuse gas around it
to form a gaseous atmosphere.
327
00:18:55,510 --> 00:18:59,443
It's a simple idea,
but with a big problem...
328
00:18:59,510 --> 00:19:01,043
Time.
329
00:19:01,143 --> 00:19:03,443
By that old model,
it would take upwards of
330
00:19:03,510 --> 00:19:06,943
100 million years to accumulate
enough planetesimals to do that.
331
00:19:08,043 --> 00:19:10,143
Way too long for Jupiter to grow
332
00:19:10,209 --> 00:19:13,043
before the Sun blows all
the gas away.
333
00:19:14,810 --> 00:19:16,810
We found a clue to how Jupiter
334
00:19:16,910 --> 00:19:19,786
beat the problem of
the disappearing gas
335
00:19:19,810 --> 00:19:24,043
in 2017, when the Juno
spacecraft investigated
336
00:19:24,143 --> 00:19:25,810
the gas giant's core.
337
00:19:25,910 --> 00:19:28,886
The traditional
theories predict that
338
00:19:28,910 --> 00:19:30,943
Jupiter's core would be
kind of like a big ball
339
00:19:31,043 --> 00:19:34,343
of solid iron or rock,
surrounded by
340
00:19:34,410 --> 00:19:37,010
a giant gaseous atmosphere.
341
00:19:40,710 --> 00:19:44,910
Juno instead found
that Jupiter's core is fuzzy.
342
00:19:45,010 --> 00:19:47,943
There's no boundary
between hard rock
343
00:19:48,043 --> 00:19:49,610
and then gaseous atmosphere.
344
00:19:49,710 --> 00:19:52,510
There's just a gradual
transition as you move
345
00:19:52,610 --> 00:19:56,710
outwards from mostly rock
and icy to mostly gassy.
346
00:19:58,443 --> 00:20:02,043
This fuzzy transition from
rock ice core to gas
347
00:20:02,109 --> 00:20:03,386
suggests that young Jupiter
348
00:20:03,410 --> 00:20:06,910
didn't eat a la carte with
separate courses of
349
00:20:07,010 --> 00:20:08,643
planetesimals and then gas.
350
00:20:11,343 --> 00:20:16,185
Instead, it devoured the whole
buffet in one sitting.
351
00:20:16,209 --> 00:20:18,943
These fuzzy cores suggest that,
352
00:20:19,043 --> 00:20:21,285
as Jupiter's core was forming,
353
00:20:21,309 --> 00:20:24,686
it was actually incorporating
a mixture of gas and ice
354
00:20:24,710 --> 00:20:28,243
and rocks all together
in its formation.
355
00:20:28,309 --> 00:20:30,686
This was possible
because there was still
356
00:20:30,710 --> 00:20:33,943
lots of gas in
the protoplanetary disk.
357
00:20:36,410 --> 00:20:37,943
Everything was moving through
358
00:20:38,043 --> 00:20:40,443
this very thick disk
of dust and gas.
359
00:20:40,510 --> 00:20:41,986
That means that everything
was actually
360
00:20:42,010 --> 00:20:44,343
being slowed down by the drag.
361
00:20:44,410 --> 00:20:46,043
Things were the size of pebbles,
362
00:20:46,143 --> 00:20:47,986
they were feeling the drag, too.
363
00:20:48,010 --> 00:20:51,343
That meant they lost energy
and made it easier for Jupiter
364
00:20:51,410 --> 00:20:52,810
to pull them in.
365
00:20:54,109 --> 00:20:56,743
The young planetesimals
grab millions
366
00:20:56,810 --> 00:20:59,643
of pebbles along with
lots of gas.
367
00:20:59,710 --> 00:21:03,810
They're drawing in gas
as well as these pebbles.
368
00:21:03,910 --> 00:21:06,910
The pebbles basically run out,
and they keep drawing
369
00:21:07,010 --> 00:21:08,915
this gas in and get bigger
and bigger and bigger.
370
00:21:10,243 --> 00:21:13,743
This formation model
allows you to grow a planet like
371
00:21:13,810 --> 00:21:15,309
Jupiter much more quickly,
372
00:21:15,410 --> 00:21:17,410
because it's gobbling up
everything at once at
373
00:21:17,510 --> 00:21:20,986
a very rapid pace, and that
allows it to potentially beat
374
00:21:21,010 --> 00:21:22,743
the Sun and grow within a few
375
00:21:22,810 --> 00:21:26,010
million years before the Sun
blows everything away.
376
00:21:27,943 --> 00:21:29,743
Both Jupiter and Saturn
377
00:21:29,810 --> 00:21:33,309
won their race against the Sun
and grew large.
378
00:21:34,810 --> 00:21:38,043
But the inner planets
were not so lucky.
379
00:21:40,243 --> 00:21:44,786
The Godfather ruthlessly
limited the food on their menu.
380
00:21:44,810 --> 00:21:47,343
And so the planets that formed
381
00:21:47,410 --> 00:21:50,486
depend upon what you have to
begin with... if you're making
382
00:21:50,510 --> 00:21:52,710
a cake, and you only have
certain ingredients,
383
00:21:52,810 --> 00:21:54,910
you can only make a cake out
of those ingredients,
384
00:21:55,010 --> 00:21:56,610
and the planets
are the same way.
385
00:21:56,710 --> 00:21:58,185
They could only be made out
386
00:21:58,209 --> 00:22:00,209
of things that are in
their vicinity.
387
00:22:00,309 --> 00:22:03,043
In the inner solar system,
where it's much warmer,
388
00:22:03,143 --> 00:22:05,710
volatiles like water and ammonia
389
00:22:05,810 --> 00:22:07,986
had evaporated
and get blown away.
390
00:22:08,010 --> 00:22:11,743
So the only materials found
here for building planets
391
00:22:11,810 --> 00:22:15,043
were rocky, metallic materials.
392
00:22:15,109 --> 00:22:16,786
So the planets
that formed in this
393
00:22:16,810 --> 00:22:20,710
inner region are rocky planets
with metallic cores.
394
00:22:23,243 --> 00:22:25,910
The ice giants feasted
on materials that
395
00:22:26,010 --> 00:22:29,743
only survive far from
the Sun's harmful influence.
396
00:22:31,043 --> 00:22:32,410
When you get further out,
397
00:22:32,510 --> 00:22:35,810
the distances that Uranus
and Neptune are at, ammonia
398
00:22:35,910 --> 00:22:39,285
and methane start to turn into
their own frozen ices.
399
00:22:39,309 --> 00:22:40,886
That's why we call them
ice giants, because
400
00:22:40,910 --> 00:22:44,386
they're formed primarily
out of these solid ices.
401
00:22:44,410 --> 00:22:48,010
And there were plenty
of these ices to gorge on.
402
00:22:49,810 --> 00:22:51,443
The further you are
from the Sun,
403
00:22:51,510 --> 00:22:53,810
the less the effect
the solar wind has.
404
00:22:53,910 --> 00:22:55,986
It's a bit like if you're
standing next to a fan, where if
405
00:22:56,010 --> 00:22:57,486
you're right next to it,
you're really gonna feel it.
406
00:22:57,510 --> 00:22:58,743
You step back a few paces,
407
00:22:58,810 --> 00:23:00,510
it's not as blowy, and so it's
408
00:23:00,610 --> 00:23:02,643
the same thing happening in
the outer solar system.
409
00:23:02,710 --> 00:23:04,143
It's not able to strip away
410
00:23:04,209 --> 00:23:06,886
the gasses and the rock quite
as much.
411
00:23:06,910 --> 00:23:08,810
The ice giants grew to over
412
00:23:08,910 --> 00:23:11,986
14 times the mass of Earth.
413
00:23:12,010 --> 00:23:14,786
The Godfather, the Sun,
414
00:23:14,810 --> 00:23:16,910
ruthlessly controls the family.
415
00:23:17,010 --> 00:23:20,843
But firstborn Jupiter has
grown large.
416
00:23:20,910 --> 00:23:22,943
He craves power
417
00:23:23,043 --> 00:23:26,886
and attempts a hostile takeover
of the inner solar system,
418
00:23:26,910 --> 00:23:29,710
triggering mass murder
and mayhem.
419
00:23:41,043 --> 00:23:42,986
We used to think
that all star systems
420
00:23:43,010 --> 00:23:45,043
were similar to our own.
421
00:23:45,109 --> 00:23:49,285
That's because our solar system
was the only one we knew.
422
00:23:49,309 --> 00:23:51,886
It's hard to get
a perspective on
423
00:23:51,910 --> 00:23:53,843
your home if you've not been
anywhere else.
424
00:23:53,910 --> 00:23:57,309
We thought it was typical,
but now that we've discovered
425
00:23:57,410 --> 00:24:00,285
hundreds of others,
it's the weird one.
426
00:24:00,309 --> 00:24:02,285
It may surprise you to learn
that we've never found
427
00:24:02,309 --> 00:24:04,386
a solar system
around another star
428
00:24:04,410 --> 00:24:06,143
that really resembles our own,
429
00:24:06,209 --> 00:24:08,285
with all of these small, rocky
planets in the middle of
430
00:24:08,309 --> 00:24:10,586
the solar system
and these big gas giants
431
00:24:10,610 --> 00:24:12,410
farther out.
432
00:24:12,510 --> 00:24:17,710
We've found star systems
with super puff planets,
433
00:24:17,810 --> 00:24:21,486
rocky worlds orbiting
tiny red stars,
434
00:24:21,510 --> 00:24:24,710
giant stars
with superheated planets
435
00:24:24,810 --> 00:24:26,810
that rain liquid iron,
436
00:24:26,910 --> 00:24:30,043
water worlds,
and planets orbiting zombie
437
00:24:30,109 --> 00:24:31,543
white dwarf stars,
438
00:24:31,610 --> 00:24:34,710
but none that look like
our home system.
439
00:24:34,810 --> 00:24:37,543
Every solar system
we look at, ours
440
00:24:37,610 --> 00:24:41,043
just look like it's standing
off in a corner all by itself.
441
00:24:42,810 --> 00:24:46,510
The other systems may be
very different from our own,
442
00:24:46,610 --> 00:24:50,510
but they can still show us how
the solar system developed.
443
00:24:52,910 --> 00:24:54,943
2021.
444
00:24:55,043 --> 00:24:57,243
Scientists discover
six planets orbiting
445
00:24:57,309 --> 00:24:58,986
a small orange star
446
00:24:59,010 --> 00:25:01,610
called TOI-178.
447
00:25:02,610 --> 00:25:04,843
And they range from just
a little bit more massive than
448
00:25:04,910 --> 00:25:06,810
the Earth,
about 1.5 times,
449
00:25:06,910 --> 00:25:09,843
to a bit more than seven times
the mass of the Earth.
450
00:25:09,910 --> 00:25:13,043
These are called
super-Earths, and it turns out,
451
00:25:13,143 --> 00:25:15,743
these are really abundant
out in the universe.
452
00:25:16,810 --> 00:25:20,209
Around 40 percent
of the star systems we've found
453
00:25:20,309 --> 00:25:24,285
contain at least one
super-Earth.
454
00:25:24,309 --> 00:25:27,610
One of the most peculiar
aspects about our solar system
455
00:25:27,710 --> 00:25:29,743
is that we don't have
any super-Earths.
456
00:25:29,810 --> 00:25:31,643
We see these things everywhere.
457
00:25:31,710 --> 00:25:33,010
Not here.
458
00:25:36,610 --> 00:25:38,486
The first clue to
solving the mystery of
459
00:25:38,510 --> 00:25:43,285
the missing super-Earths comes
from an asteroid called Psyche.
460
00:25:43,309 --> 00:25:45,786
It orbits in the asteroid belt,
461
00:25:45,810 --> 00:25:50,510
a band of rocky objects
between Mars and Jupiter.
462
00:25:50,610 --> 00:25:53,986
The asteroid Psyche appears
to be a fascinating world
463
00:25:54,010 --> 00:25:57,043
made almost entirely of metal,
of iron and nickel.
464
00:25:59,910 --> 00:26:04,243
We think it's the core
of a now destroyed planet.
465
00:26:04,309 --> 00:26:07,543
You can think of Psyche
as a metallic kernel of
466
00:26:07,610 --> 00:26:11,109
a nut whose shell was smashed
off in a huge collision.
467
00:26:16,810 --> 00:26:20,243
The asteroid belt
is full of similar debris,
468
00:26:20,309 --> 00:26:23,743
like blood splatter
at a mafia murder scene.
469
00:26:28,610 --> 00:26:30,743
It points to serious
felonies taking
470
00:26:30,810 --> 00:26:33,043
place in the early solar system.
471
00:26:33,109 --> 00:26:37,743
We think that there were
once dozens of
472
00:26:37,810 --> 00:26:40,943
rocky protoplanets orbiting
around the young sun.
473
00:26:43,510 --> 00:26:45,109
Now we only have four.
474
00:26:47,743 --> 00:26:49,986
We find clues to what caused
475
00:26:50,010 --> 00:26:53,710
this planetary homicide in
distant star systems.
476
00:26:55,143 --> 00:26:57,886
The first exoplanets
that we found orbiting stars
477
00:26:57,910 --> 00:27:00,185
like the Sun are what we call
hot Jupiters.
478
00:27:00,209 --> 00:27:02,143
Nobody expected these.
479
00:27:02,209 --> 00:27:05,043
These are planets
as big or bigger
480
00:27:05,143 --> 00:27:06,610
than Jupiter, but orbiting
481
00:27:06,710 --> 00:27:09,043
super close in to their star.
482
00:27:09,109 --> 00:27:11,486
When the young star is forming,
483
00:27:11,510 --> 00:27:13,443
it blows out all of the material
484
00:27:13,510 --> 00:27:14,387
that's very close to it,
485
00:27:14,411 --> 00:27:16,710
the sheer force
of the solar winds, so
486
00:27:16,810 --> 00:27:18,586
there's nothing that could
have formed right there.
487
00:27:18,610 --> 00:27:19,643
How the heck did you get
488
00:27:19,710 --> 00:27:23,043
a planet that big,
that close to a star?
489
00:27:23,143 --> 00:27:26,243
Hot Jupiters forced scientists
490
00:27:26,309 --> 00:27:28,610
to consider a radical idea.
491
00:27:28,710 --> 00:27:31,343
We always assumed
that planets were
492
00:27:31,410 --> 00:27:33,410
formed where we see them today.
493
00:27:33,510 --> 00:27:35,786
But these hot Jupiters couldn't
have been formed there.
494
00:27:35,810 --> 00:27:39,810
They must have migrated in
from further out.
495
00:27:39,910 --> 00:27:41,743
That made us look
at our solar system
496
00:27:41,810 --> 00:27:43,586
through a different lens.
497
00:27:43,610 --> 00:27:47,886
And all of a sudden, we started
seeing signs that, oh, maybe...
498
00:27:47,910 --> 00:27:49,910
Yeah, maybe this happened here.
499
00:27:50,010 --> 00:27:53,386
One million years after
500
00:27:53,410 --> 00:27:56,743
the birth of the mafia
family-like solar system,
501
00:27:56,810 --> 00:27:59,043
many small rocky planets grow in
502
00:27:59,143 --> 00:28:02,386
the inner part of
the protoplanetary disk.
503
00:28:02,410 --> 00:28:06,743
Underboss Jupiter makes
a move to take control of
504
00:28:06,810 --> 00:28:08,085
the family.
505
00:28:08,109 --> 00:28:12,586
The giant planet's gravity
creates spiraling waves in
506
00:28:12,610 --> 00:28:16,510
the protoplanetary disk,
which drag on Jupiter,
507
00:28:16,610 --> 00:28:17,810
slowing it down.
508
00:28:22,810 --> 00:28:25,586
So Jupiter slows down just
a little bit in its orbit around
509
00:28:25,610 --> 00:28:27,686
the Sun, and as it slows down,
510
00:28:27,710 --> 00:28:32,043
it falls inwards towards
the Sun and migrates closer
511
00:28:32,143 --> 00:28:33,510
and closer.
512
00:28:33,610 --> 00:28:35,610
Jupiter crashes into
513
00:28:35,710 --> 00:28:39,410
the inner solar system...
In its path,
514
00:28:39,510 --> 00:28:41,343
the infant rocky planets.
515
00:28:43,209 --> 00:28:46,743
You can't take something with
300 times the mass of the Earth
516
00:28:46,810 --> 00:28:48,986
and let it roam around
the inner solar system
517
00:28:49,010 --> 00:28:51,610
and hope it's not gonna
do anything... Jupiter is like
518
00:28:51,710 --> 00:28:54,486
a monster truck at a stock car
rally race, right?
519
00:28:54,510 --> 00:28:56,386
It's just plowing through
everything,
520
00:28:56,410 --> 00:28:57,610
just chaos everywhere.
521
00:29:02,443 --> 00:29:04,910
So here we are, forming
our lovely young solar system,
522
00:29:05,010 --> 00:29:06,543
and there are
all kinds of new planets
523
00:29:06,610 --> 00:29:09,586
forming, and they're settling
into nice orderly orbits.
524
00:29:09,610 --> 00:29:11,486
And here comes Jupiter,
525
00:29:11,510 --> 00:29:12,810
the big bully on the block.
526
00:29:14,410 --> 00:29:18,843
Enforcer Jupiter pushes
its smaller siblings around.
527
00:29:18,910 --> 00:29:22,843
Gravitationally, it starts to
destabilize the inner planets,
528
00:29:22,910 --> 00:29:25,910
so nice circular orbits
start to go all haywire,
529
00:29:26,910 --> 00:29:28,180
and things begin to
actually play
530
00:29:28,209 --> 00:29:30,410
pinball in the early
solar system.
531
00:29:31,510 --> 00:29:35,886
The growing inner planets
fly off in all directions.
532
00:29:35,910 --> 00:29:38,043
Some collide violently.
533
00:29:39,043 --> 00:29:40,343
Many die in the melee.
534
00:29:43,810 --> 00:29:46,643
This is like
solar system demolition derby
535
00:29:46,710 --> 00:29:48,743
in the early days
of the formation of the planets,
536
00:29:48,810 --> 00:29:50,386
where things are
smashing into each other
537
00:29:50,410 --> 00:29:53,043
and destroying little planets
right and left.
538
00:29:55,910 --> 00:29:58,410
This cosmic carnage
could explain why
539
00:29:58,510 --> 00:30:00,743
we don't have any super-Earths.
540
00:30:06,343 --> 00:30:10,010
Perhaps our solar system once
had large, rocky planets,
541
00:30:11,209 --> 00:30:12,810
but debris from the colliding
542
00:30:12,910 --> 00:30:15,410
inner planets slowed down
their orbits,
543
00:30:16,910 --> 00:30:21,543
dragging the young
super-Earths into the Sun.
544
00:30:21,610 --> 00:30:24,786
These primordial super-Earths
get pushed
545
00:30:24,810 --> 00:30:27,043
onto the Sun
and destroyed altogether.
546
00:30:32,643 --> 00:30:36,343
It only takes 100,000
years to destroy
547
00:30:36,410 --> 00:30:38,886
the primordial group
of super-Earths that
548
00:30:38,910 --> 00:30:41,143
would have formed
in the inner solar system.
549
00:30:41,209 --> 00:30:45,285
But not everyone agrees
with this version of events.
550
00:30:45,309 --> 00:30:49,309
This is a pretty cool idea,
but I'm not convinced by it.
551
00:30:49,410 --> 00:30:52,143
We have a lot of ideas of why
we are the way we are today.
552
00:30:52,209 --> 00:30:54,543
What we need is more evidence
to be able to separate
553
00:30:54,610 --> 00:30:55,643
these ideas out.
554
00:30:57,209 --> 00:30:59,085
An alternative theory
suggests that
555
00:30:59,109 --> 00:31:02,610
Jupiter stole everyone
else's lunch,
556
00:31:02,710 --> 00:31:06,510
starving the inner solar
system of food
557
00:31:06,610 --> 00:31:10,243
so the planets couldn't
grow into super-Earths.
558
00:31:11,810 --> 00:31:14,285
Without Jupiter, Earth
and Venus and Mars might
559
00:31:14,309 --> 00:31:16,285
have just kept on growing
and growing and growing.
560
00:31:16,309 --> 00:31:17,586
We might have ended up with
a bunch
561
00:31:17,610 --> 00:31:19,237
of super-Earths
in the inner solar system.
562
00:31:20,610 --> 00:31:23,610
Mob underboss
Jupiter's unprovoked assault
563
00:31:23,710 --> 00:31:27,209
on his smaller siblings in the
inner solar system continued.
564
00:31:28,309 --> 00:31:31,810
The attack caused many
casualties and nearly put
565
00:31:31,910 --> 00:31:34,710
our planet in an early grave.
566
00:31:45,543 --> 00:31:49,285
For thousands of years,
people have looked up at
567
00:31:49,309 --> 00:31:54,085
the sky and seen the planets
orbiting the Sun in harmony.
568
00:31:54,109 --> 00:31:57,386
They've seen all
of this wonderful order.
569
00:31:57,410 --> 00:31:59,043
And that's what we thought.
570
00:31:59,143 --> 00:32:01,243
Everything formed together,
the Sun,
571
00:32:01,309 --> 00:32:04,243
the planets, almost like this
beautiful clockwork set up in
572
00:32:04,309 --> 00:32:05,443
the heavens.
573
00:32:05,510 --> 00:32:08,710
Now we know that actually that
was far from the truth.
574
00:32:13,410 --> 00:32:15,486
Around two million
years after the birth
575
00:32:15,510 --> 00:32:18,710
of the Godfather, the Sun,
the underboss,
576
00:32:18,810 --> 00:32:22,243
Jupiter, makes a power grab
and crashes
577
00:32:22,309 --> 00:32:23,743
into the inner solar system.
578
00:32:33,309 --> 00:32:35,610
If Jupiter had continued
its journey toward the Sun,
579
00:32:35,710 --> 00:32:38,185
it would have ejected a lot
of the stuff that was left.
580
00:32:38,209 --> 00:32:40,209
There would be
no inner rocky planets.
581
00:32:40,309 --> 00:32:41,643
It would just be Jupiter.
582
00:32:43,043 --> 00:32:46,710
Fortunately,
we avoid complete slaughter.
583
00:32:46,810 --> 00:32:50,886
Something stops Jupiter's
murderous attack.
584
00:32:50,910 --> 00:32:53,486
Lucky for us,
we had an ace in the hole.
585
00:32:53,510 --> 00:32:55,786
We had a friend,
and that friend is so
586
00:32:55,810 --> 00:32:59,143
beautiful in the sky today,
and we call that friend Saturn.
587
00:33:03,043 --> 00:33:07,043
Saturn is also migrating
inward toward the Sun,
588
00:33:07,143 --> 00:33:10,386
but the rate it's moving in
depends on the mass of
589
00:33:10,410 --> 00:33:12,886
the planet... Saturn is
less massive than Jupiter,
590
00:33:12,910 --> 00:33:14,710
so it's moving in more rapidly.
591
00:33:16,143 --> 00:33:19,910
Peace-making consigliere,
Saturn, catches up
592
00:33:20,010 --> 00:33:22,743
with Jupiter and brokers a deal.
593
00:33:22,810 --> 00:33:25,309
When they reach each other,
they don't collide.
594
00:33:25,410 --> 00:33:28,943
They get stuck in a complicated
orbital dance with each other.
595
00:33:29,043 --> 00:33:32,586
Their cosmic tango
strips out gas from the disc,
596
00:33:32,610 --> 00:33:38,043
clearing a path for Saturn and
Jupiter to move back outwards.
597
00:33:38,143 --> 00:33:39,786
So this can actually reverse
598
00:33:39,810 --> 00:33:42,143
their migration, and all of
a sudden, we have
599
00:33:42,209 --> 00:33:44,343
the two planets moving outward
in the solar system.
600
00:33:44,410 --> 00:33:47,143
So it's like Saturn has
a trailer hitch, and it's towing
601
00:33:47,209 --> 00:33:49,285
Jupiter back to the outer
solar system,
602
00:33:49,309 --> 00:33:50,309
where we find them today.
603
00:33:53,543 --> 00:33:56,886
Saturn saved
the earth, basically.
604
00:33:56,910 --> 00:33:59,386
If it hadn't have been there
to pull Jupiter back out from
605
00:33:59,410 --> 00:34:00,610
the inner solar system,
606
00:34:00,643 --> 00:34:02,943
Jupiter would have thrown all
the inner planets out.
607
00:34:03,043 --> 00:34:07,285
So no Mercury, no Venus,
no Mars, no Earth.
608
00:34:07,309 --> 00:34:11,085
Three million years after
the birth of the Sun,
609
00:34:11,109 --> 00:34:14,243
around 20 baby planets
survive Jupiter's
610
00:34:14,309 --> 00:34:16,843
ransacking of
the inner solar system,
611
00:34:16,910 --> 00:34:19,410
but the carnage isn't over.
612
00:34:21,910 --> 00:34:24,443
The inner solar system's
kind of in turmoil.
613
00:34:24,510 --> 00:34:27,010
The gravitational interaction
from Jupiter was severe.
614
00:34:28,710 --> 00:34:31,085
Everything is excited,
orbits are out of control
615
00:34:31,109 --> 00:34:33,309
and crazy, and things are
interacting and having big,
616
00:34:33,410 --> 00:34:34,610
violent collisions.
617
00:34:38,143 --> 00:34:41,209
The inner solar system
is like a congested highway.
618
00:34:44,043 --> 00:34:47,643
Planets cross lanes,
collisions are frequent.
619
00:34:50,643 --> 00:34:52,610
As the bloodshed continues,
620
00:34:52,710 --> 00:34:56,610
the young Earth wanders into
the path of a smaller planet.
621
00:34:58,143 --> 00:35:00,085
There's a theory,
and it's a pretty good one,
622
00:35:00,109 --> 00:35:02,043
that the Earth, a long time ago,
623
00:35:02,143 --> 00:35:04,810
was hit by another
relatively big planet,
624
00:35:04,910 --> 00:35:06,101
and we call that planet Theia.
625
00:35:08,943 --> 00:35:12,810
Theia hit Earth at over
25,000 miles an hour.
626
00:35:14,843 --> 00:35:16,743
The impact destroyed Theia
627
00:35:18,143 --> 00:35:19,510
and nearly wiped out Earth.
628
00:35:21,143 --> 00:35:23,843
When Earth was struck by Theia,
629
00:35:23,910 --> 00:35:27,386
it was unlike any event
before or since.
630
00:35:27,410 --> 00:35:29,386
We think about the event
that wiped
631
00:35:29,410 --> 00:35:31,343
out the dinosaurs
as a huge collision.
632
00:35:31,410 --> 00:35:34,143
Oh, this one dwarfs that one.
633
00:35:37,710 --> 00:35:40,910
The Earth was completely
turned inside out.
634
00:35:41,010 --> 00:35:45,843
The surface was new, it was
molten, and it was raining fire,
635
00:35:45,910 --> 00:35:49,910
literally... lava rock was
raining down from the heavens.
636
00:35:53,510 --> 00:35:55,810
Earth was badly
wounded but survived.
637
00:36:00,109 --> 00:36:03,085
Material from Theia
mixed with Earth rock,
638
00:36:03,109 --> 00:36:07,143
building a bigger planet
and a new companion.
639
00:36:08,543 --> 00:36:10,043
This collision was so huge,
640
00:36:10,143 --> 00:36:12,285
it blasted off a tremendous
amount of material off
641
00:36:12,309 --> 00:36:15,443
the Earth's surface, and this
coalesced to form the Moon.
642
00:36:19,910 --> 00:36:22,109
That theory may now become fact.
643
00:36:24,309 --> 00:36:26,343
We found two massive chunks of
644
00:36:26,410 --> 00:36:29,209
rock buried deep beneath
Earth's surface.
645
00:36:30,410 --> 00:36:33,786
These massive lumps of rock
have a different density,
646
00:36:33,810 --> 00:36:35,443
a different composition,
647
00:36:35,510 --> 00:36:37,410
than the rest of
the mantle rock around them.
648
00:36:38,710 --> 00:36:41,986
A new study in 2021 suggests
649
00:36:42,010 --> 00:36:43,410
they don't come from Earth.
650
00:36:46,109 --> 00:36:47,886
It could be that
these dense blobs of
651
00:36:47,910 --> 00:36:50,743
material deep in our mantle
are remnants of Theia.
652
00:36:53,410 --> 00:36:54,943
Throughout
the inner solar system
653
00:36:55,043 --> 00:36:57,510
protoplanet hit protoplanet.
654
00:37:00,643 --> 00:37:04,443
Some high speed crashes
ended in catastrophe.
655
00:37:05,943 --> 00:37:08,443
There was drama, a lot of drama.
656
00:37:08,510 --> 00:37:10,285
It's as much
a story of destruction
657
00:37:10,309 --> 00:37:11,643
as it is of creation.
658
00:37:11,710 --> 00:37:14,143
There are a lot of planets
that could have made it
659
00:37:14,209 --> 00:37:15,443
but didn't.
660
00:37:15,510 --> 00:37:18,010
And we just happened to be one
of the lucky ones that did.
661
00:37:20,343 --> 00:37:24,743
Slower impacts glued
the colliding worlds together,
662
00:37:24,810 --> 00:37:27,743
building hybrid planets
from the wreckage.
663
00:37:30,810 --> 00:37:34,243
The four terrestrial planets...
Mercury, Venus,
664
00:37:34,309 --> 00:37:37,343
Earth, and Mars...
Emerged from the ashes
665
00:37:37,410 --> 00:37:41,043
of the 20 protoplanets
and joined the mob family.
666
00:37:41,109 --> 00:37:43,343
The planets are connected.
667
00:37:43,410 --> 00:37:45,643
You probably have some
material in your body
668
00:37:45,710 --> 00:37:47,209
from pretty much every world
669
00:37:47,309 --> 00:37:48,686
that ever existed
in the solar system.
670
00:37:48,710 --> 00:37:50,843
Everything mixed around.
671
00:37:50,910 --> 00:37:53,410
That mixing made Earth
672
00:37:53,510 --> 00:37:56,309
larger and better
equipped to survive.
673
00:37:57,643 --> 00:37:59,986
The bloodbath also left its mark
674
00:38:00,010 --> 00:38:01,643
on the other surviving planets.
675
00:38:03,343 --> 00:38:04,886
What's strange
about Venus is that
676
00:38:04,910 --> 00:38:07,486
it actually spins in
the opposite direction.
677
00:38:07,510 --> 00:38:09,486
All the other planets spin
sort of with...
678
00:38:09,510 --> 00:38:12,443
With a righthand spin,
from the west to the east,
679
00:38:12,510 --> 00:38:15,710
and Venus spins from the east
to the west.
680
00:38:15,810 --> 00:38:18,886
And also
Venus's spin is very slow.
681
00:38:18,910 --> 00:38:22,443
It's 243 times slower
than that of Earth's.
682
00:38:22,510 --> 00:38:26,043
You can imagine a big
protoplanetary embryo,
683
00:38:26,109 --> 00:38:27,943
almost the size of Venus
itself, smashing
684
00:38:28,043 --> 00:38:29,510
almost head-on to Venus,
685
00:38:30,810 --> 00:38:34,643
just in the right angle to
stop the rotation,
686
00:38:34,710 --> 00:38:37,943
slow it down, even actually
reverse it slightly.
687
00:38:38,043 --> 00:38:41,043
And now, it's still spinning
like that today.
688
00:38:43,710 --> 00:38:46,943
Mercury carries horrific
scars from Jupiter's
689
00:38:47,043 --> 00:38:49,610
assault on the inner
solar system.
690
00:38:51,109 --> 00:38:53,910
Mercury has always
seemed to be a bit of
691
00:38:54,010 --> 00:38:56,019
an odd planet, because it really
is sort of a cannonball.
692
00:38:56,043 --> 00:38:58,843
It has a giant core compared
to the rest of the planet.
693
00:38:58,910 --> 00:39:01,143
So the question is,
how do you get
694
00:39:01,209 --> 00:39:03,743
this large core,
but very little rock,
695
00:39:03,810 --> 00:39:05,410
very little mantle
and crust around it?
696
00:39:06,643 --> 00:39:10,209
We think Mercury
hit another planet, hard.
697
00:39:11,343 --> 00:39:15,510
The outer layers of
Mercury, its rocky mantle,
698
00:39:15,610 --> 00:39:18,185
was blasted off, leaving behind
699
00:39:18,209 --> 00:39:22,843
just the dense iron cannonball
core of this planet,
700
00:39:22,910 --> 00:39:26,610
which ricocheted off and then
settled in Mercury's
701
00:39:26,710 --> 00:39:28,843
current orbit, close to the Sun.
702
00:39:33,410 --> 00:39:35,786
That leaves
one last rocky planet
703
00:39:35,810 --> 00:39:39,810
member of the mafia
family... Mars.
704
00:39:42,610 --> 00:39:45,610
It's older and much smaller
than its neighbors,
705
00:39:45,710 --> 00:39:46,943
Venus and Earth.
706
00:39:49,510 --> 00:39:52,085
One way to interpret
Mars in this scenario is that
707
00:39:52,109 --> 00:39:53,610
Mars was one of those original
708
00:39:53,710 --> 00:39:56,185
20 or 30 planetary embryos,
or protoplanets,
709
00:39:56,209 --> 00:39:58,443
and it just survived.
710
00:39:58,510 --> 00:40:00,886
It avoided
this big violent end game
711
00:40:00,910 --> 00:40:03,243
of the giant impact stage of
planet formation.
712
00:40:04,410 --> 00:40:06,786
Mars sat on the sidelines,
713
00:40:06,810 --> 00:40:08,443
far enough away
from the action to
714
00:40:08,510 --> 00:40:10,810
be safe from physical harm,
715
00:40:10,910 --> 00:40:15,043
but enforcer Jupiter's violent
raid on the inner solar system
716
00:40:15,109 --> 00:40:20,043
still prevented Mars from
reaching its full potential.
717
00:40:20,109 --> 00:40:22,743
One big effect
of Jupiter's incursion
718
00:40:22,810 --> 00:40:23,743
into the inner solar system is
719
00:40:23,810 --> 00:40:26,043
to blast away
a bunch of material,
720
00:40:26,109 --> 00:40:28,309
around where we find Mars today.
721
00:40:28,410 --> 00:40:30,743
In some ways,
Jupiter kinda ate Mars's lunch.
722
00:40:30,810 --> 00:40:32,686
So Mars just didn't have as
much stuff to
723
00:40:32,710 --> 00:40:35,143
work with, and it never became
a very big planet.
724
00:40:36,243 --> 00:40:39,710
After 60 million years of
family feuding,
725
00:40:39,810 --> 00:40:43,543
the battle of the planets is
finally over.
726
00:40:43,610 --> 00:40:46,243
Out of all the mayhem
and chaos of the early
727
00:40:46,309 --> 00:40:49,486
solar system, four
terrestrial planets remained.
728
00:40:49,510 --> 00:40:52,143
One of them was Earth.
729
00:40:52,209 --> 00:40:54,510
Given everything we've
now learned about how violent
730
00:40:54,610 --> 00:40:57,486
it was, we understand just
how vulnerable we've been
731
00:40:57,510 --> 00:41:00,209
all the way along...
Planets colliding, planets
732
00:41:00,309 --> 00:41:03,586
even changing places...
In some ways now, it's amazing
733
00:41:03,610 --> 00:41:06,043
the Earth even survived.
734
00:41:06,109 --> 00:41:09,386
Our planet emerged as one
of the winners from underboss
735
00:41:09,410 --> 00:41:12,710
Jupiter's homicidal assault
on the inner planets.
736
00:41:12,810 --> 00:41:16,810
But Jupiter's return to
the outer solar system soon
737
00:41:16,910 --> 00:41:18,510
triggered more mayhem,
738
00:41:18,610 --> 00:41:21,610
mayhem that would threaten
Earth with the biggest
739
00:41:21,710 --> 00:41:24,309
bombardment in its history.
740
00:41:38,343 --> 00:41:41,786
The mafia family
we call the solar system has
741
00:41:41,810 --> 00:41:45,543
survived underboss Jupiter's
attack on the inner planets
742
00:41:46,743 --> 00:41:50,543
but faces more disruption from
its enforcer
743
00:41:50,610 --> 00:41:52,543
when the giant gas planet heads
744
00:41:52,610 --> 00:41:56,143
out towards
where Uranus and Neptune grow,
745
00:41:56,209 --> 00:41:59,185
a journey that may help
explain several mysteries about
746
00:41:59,209 --> 00:42:00,343
the solar system,
747
00:42:00,410 --> 00:42:03,510
including the size
of the ice giants.
748
00:42:04,710 --> 00:42:06,910
The biggest problem with
the outer solar system is
749
00:42:07,010 --> 00:42:08,309
literally bigness.
750
00:42:08,410 --> 00:42:11,910
Uranus and Neptune are too big
for where they are.
751
00:42:12,010 --> 00:42:14,386
The problem is
the availability of
752
00:42:14,410 --> 00:42:16,043
building materials.
753
00:42:16,143 --> 00:42:17,943
This far out from the Sun,
754
00:42:18,043 --> 00:42:21,743
there wasn't enough gas and
dust in the protoplanetary disk
755
00:42:21,810 --> 00:42:24,910
to construct such large planets.
756
00:42:25,010 --> 00:42:28,886
One way of solving the riddle
of how Uranus and Neptune
757
00:42:28,910 --> 00:42:32,143
are so big is that they didn't
form where they are now.
758
00:42:32,209 --> 00:42:33,285
So we think that they formed
759
00:42:33,309 --> 00:42:36,109
further in
and then maybe moved out.
760
00:42:37,643 --> 00:42:39,810
This is what we think happened.
761
00:42:40,843 --> 00:42:43,810
Five million years after
the birth of the Sun,
762
00:42:43,910 --> 00:42:47,810
Jupiter and Saturn reached
the same region of space as
763
00:42:47,910 --> 00:42:49,786
Uranus and Neptune.
764
00:42:49,810 --> 00:42:54,643
The four quarreling children
call a truce and orbit together.
765
00:42:54,710 --> 00:42:57,643
Orbits are on
the razor's edge of stability
766
00:42:57,710 --> 00:43:00,710
as it is, and so one thing that
helped to stabilize
767
00:43:00,810 --> 00:43:02,686
our solar system
in the early days
768
00:43:02,710 --> 00:43:06,543
was that it was in
this cloud of gas and dust
769
00:43:06,610 --> 00:43:09,543
that was this
protoplanetary disk.
770
00:43:09,610 --> 00:43:12,410
Gas in
the protoplanetary disk can
771
00:43:12,510 --> 00:43:14,886
slow down planets
so they migrate.
772
00:43:14,910 --> 00:43:19,343
But it can also stabilize
their orbits.
773
00:43:20,610 --> 00:43:23,443
Like sand on
the side of a racing track
774
00:43:23,510 --> 00:43:26,143
that's there to slow
down the cars and help them get
775
00:43:26,209 --> 00:43:27,343
back on track,
776
00:43:27,410 --> 00:43:31,943
the gas allows the planets to
not veer off too much
777
00:43:32,043 --> 00:43:35,910
away from their stable
compact configuration.
778
00:43:37,243 --> 00:43:40,743
The ceasefire between
the gas planets is short-lived.
779
00:43:43,843 --> 00:43:48,185
Once the Godfather Sun blows
away the last of the gas,
780
00:43:48,209 --> 00:43:52,710
the largest Mafioso children
set off on another crime spree.
781
00:43:54,510 --> 00:43:56,443
So when the gas goes away,
782
00:43:56,510 --> 00:43:58,786
you no longer have this
dampening effect on the orbits
783
00:43:58,810 --> 00:44:01,710
of the giant planets,
and they can start
784
00:44:01,810 --> 00:44:03,085
interacting with each other.
785
00:44:03,109 --> 00:44:06,085
And Jupiter is free to be
a bully again, only this time,
786
00:44:06,109 --> 00:44:07,643
he's got a big
sidekick... Saturn.
787
00:44:09,209 --> 00:44:12,443
Former peacekeeper,
Saturn, joins forces
788
00:44:12,510 --> 00:44:14,643
with Jupiter, and they start
789
00:44:14,710 --> 00:44:16,410
messing with Uranus and Neptune.
790
00:44:18,209 --> 00:44:21,410
So the two largest kids team
up together and start pushing
791
00:44:21,510 --> 00:44:23,043
everyone else around.
792
00:44:23,109 --> 00:44:25,643
When you put really big planets
that are really massive,
793
00:44:25,710 --> 00:44:26,810
really close to each other,
794
00:44:26,910 --> 00:44:28,586
over time,
they start to push on each
795
00:44:28,610 --> 00:44:30,686
other's orbits, and their
orbits start to get excited.
796
00:44:30,710 --> 00:44:32,910
The whole thing starts
to unravel
797
00:44:33,010 --> 00:44:35,886
and eventually culminates in
a violent
798
00:44:35,910 --> 00:44:37,810
and beautiful instability.
799
00:44:41,943 --> 00:44:44,043
Gravitational shoves
from Jupiter
800
00:44:44,143 --> 00:44:47,143
and Saturn pushed
the ice giants outwards.
801
00:44:50,243 --> 00:44:53,510
Uranus still bears the scars
from this power move.
802
00:44:58,610 --> 00:45:02,043
For one thing, it's orbiting
the Sun on its side.
803
00:45:02,143 --> 00:45:03,686
Instead of having
its rotation axis
804
00:45:03,710 --> 00:45:04,986
sort of straight up and down,
805
00:45:05,010 --> 00:45:08,486
more or less, it's tipped
way over, so its pole is
806
00:45:08,510 --> 00:45:11,309
pointing more or less towards
the Sun instead of up and down.
807
00:45:11,410 --> 00:45:12,710
That's really weird.
808
00:45:14,209 --> 00:45:19,043
Recent studies suggest
a giant impact caused
809
00:45:19,109 --> 00:45:22,343
Uranus's strange orientation.
810
00:45:23,410 --> 00:45:25,085
Over four billion years ago,
811
00:45:25,109 --> 00:45:28,309
a large icy object hits
the ice giant
812
00:45:28,410 --> 00:45:29,743
with a glancing blow.
813
00:45:31,710 --> 00:45:34,786
The planet starts to tip over.
814
00:45:34,810 --> 00:45:37,543
Then, the attacker comes around
815
00:45:37,610 --> 00:45:40,209
and smashes into Uranus
a second time.
816
00:45:43,843 --> 00:45:48,810
This 1-2 punch knocks
the ice giant onto its side.
817
00:45:53,243 --> 00:45:54,410
A clue to the cause of
818
00:45:54,510 --> 00:45:58,209
the collision comes from
Neptune's moon, Triton.
819
00:45:59,810 --> 00:46:02,243
What's odd about
Triton is that it orbits
820
00:46:02,309 --> 00:46:04,043
the wrong way around Neptune,
and that's
821
00:46:04,143 --> 00:46:05,686
the wrong way for
the whole solar system,
822
00:46:05,710 --> 00:46:08,143
so everything is going in this
direction, Triton is going
823
00:46:08,209 --> 00:46:09,486
the other way.
824
00:46:09,510 --> 00:46:11,486
The other thing is that Triton
is made of slightly different
825
00:46:11,510 --> 00:46:14,143
things than it should be
at the orbit of Neptune.
826
00:46:14,209 --> 00:46:17,643
Its color, its density,
are just a little bit off.
827
00:46:17,710 --> 00:46:20,143
What we think that means is that
828
00:46:20,209 --> 00:46:22,810
it probably didn't form there.
829
00:46:25,910 --> 00:46:28,143
We find pointers to
Triton's origin
830
00:46:28,209 --> 00:46:30,410
on the dwarf planet Pluto.
831
00:46:34,910 --> 00:46:37,143
Pluto sits in the Kuiper belt,
832
00:46:37,209 --> 00:46:42,043
a band of millions of icy
objects beyond Neptune.
833
00:46:45,309 --> 00:46:46,986
When we looked
at Triton and compared it
834
00:46:47,010 --> 00:46:49,185
with Pluto from
telescopes from Earth,
835
00:46:49,209 --> 00:46:52,309
we recognize these two are
very similar to each other.
836
00:46:52,410 --> 00:46:54,209
On Triton, there's nitrogen ice,
837
00:46:54,309 --> 00:46:56,786
carbon monoxide ice,
there's carbon dioxide ice.
838
00:46:56,810 --> 00:46:59,710
These are the same types of
ices that we see on Pluto.
839
00:47:00,843 --> 00:47:04,686
This similarity in
chemical composition suggests
840
00:47:04,710 --> 00:47:08,309
that Pluto and Triton
formed in the same place,
841
00:47:10,143 --> 00:47:12,786
an ancient band of icy objects
842
00:47:12,810 --> 00:47:16,109
called the trans-Neptunian belt.
843
00:47:18,910 --> 00:47:21,986
When the giant planet orbits
go berserk, Uranus and Neptune
844
00:47:22,010 --> 00:47:24,810
get tossed into this
trans-Neptunian disk.
845
00:47:24,910 --> 00:47:29,309
It's like a big bowling bowl
coming in and knocking off
846
00:47:29,410 --> 00:47:31,943
bowling pins left and right.
847
00:47:34,810 --> 00:47:36,443
Chaos ensues,
848
00:47:36,510 --> 00:47:38,643
and as the two outer
planets get pushed through
849
00:47:38,710 --> 00:47:39,886
all of this stuff,
850
00:47:39,910 --> 00:47:42,343
throwing things left,
right, and center, all kinds of
851
00:47:42,410 --> 00:47:44,085
collisions are inevitable.
852
00:47:44,109 --> 00:47:47,510
One of these collisions
knocks Uranus over.
853
00:47:54,209 --> 00:47:57,309
Another small planet
heads towards Neptune.
854
00:47:59,543 --> 00:48:04,910
The ice giant grabs it,
creating the moon, Triton.
855
00:48:06,143 --> 00:48:08,543
The other
trans-Neptunian objects
856
00:48:08,610 --> 00:48:12,309
scatter outwards,
forming the Kuiper belt.
857
00:48:15,410 --> 00:48:18,610
Tremors from this planetary
bowling match spread far
858
00:48:18,710 --> 00:48:19,687
and wide,
859
00:48:19,711 --> 00:48:22,910
sparking a cataclysmic
onslaught of the inner
860
00:48:23,010 --> 00:48:25,743
solar system billions
of miles away.
861
00:48:27,510 --> 00:48:28,487
The Kuiper belt...
862
00:48:28,511 --> 00:48:31,143
This very, very distant
collection of small,
863
00:48:31,209 --> 00:48:32,910
rocky bodies in the outer
solar system...
864
00:48:33,010 --> 00:48:35,309
You would think that we have
no connection to that at all.
865
00:48:35,410 --> 00:48:38,043
But instead, it may be
responsible for helping life
866
00:48:38,143 --> 00:48:39,143
get started on Earth.
867
00:48:50,910 --> 00:48:53,109
4.6 billion years ago,
868
00:48:54,109 --> 00:48:58,610
a cloud of gas collapses in
a quiet suburb of the Milky Way.
869
00:49:00,109 --> 00:49:03,786
It's the birth of our mobster
family solar system.
870
00:49:03,810 --> 00:49:08,285
The Godfather, the Sun,
ignites and takes control.
871
00:49:08,309 --> 00:49:12,143
His children, the planets,
grow from the disk of gas
872
00:49:12,209 --> 00:49:16,109
and dust left over from
the birth of the star.
873
00:49:17,543 --> 00:49:21,085
Gas planets form in
the cold outer suburbs,
874
00:49:21,109 --> 00:49:24,309
rocky ones in the warm
inner real estate.
875
00:49:25,309 --> 00:49:28,043
But the Sun's fearsome nature
876
00:49:28,109 --> 00:49:30,510
threatens the young Earth.
877
00:49:30,610 --> 00:49:34,243
The early Earth,
right after its formation,
878
00:49:34,309 --> 00:49:36,386
was not a great place to
be alive.
879
00:49:36,410 --> 00:49:37,958
In fact, it would not have
been possible
880
00:49:38,010 --> 00:49:39,986
to be alive,
because it was so hot.
881
00:49:40,010 --> 00:49:42,786
It had no atmosphere.
It had been blown away.
882
00:49:42,810 --> 00:49:47,443
It wasn't even fully solid, and
it had no water to speak of.
883
00:49:48,610 --> 00:49:50,910
The Earth is too close
to the Sun to have
884
00:49:51,010 --> 00:49:53,510
formed with the amount of
water that we see today.
885
00:49:53,610 --> 00:49:55,843
The protoplanetary disk was
just too hot for water
886
00:49:55,910 --> 00:49:56,910
to condense,
887
00:49:58,043 --> 00:50:00,043
and water vapor would have
been blown away by
888
00:50:00,143 --> 00:50:02,443
the stellar wind...
For the same reason,
889
00:50:02,510 --> 00:50:06,143
it was also lacking in carbon
and volatile organic materials.
890
00:50:07,309 --> 00:50:09,386
This raises a big
mystery... where did all that
891
00:50:09,410 --> 00:50:11,085
material ultimately come from
892
00:50:11,109 --> 00:50:14,643
that we now obviously have
in abundance on planet Earth?
893
00:50:19,010 --> 00:50:22,543
NASA's Dawn mission to
the dwarf planet, Ceres,
894
00:50:22,610 --> 00:50:24,886
provided a clue.
895
00:50:24,910 --> 00:50:28,243
Ceres sits in the asteroid belt,
896
00:50:28,309 --> 00:50:31,986
a band of rocky debris left
over from Jupiter's attack on
897
00:50:32,010 --> 00:50:33,109
the inner planets.
898
00:50:34,209 --> 00:50:36,143
The Dawn mission showed us that
899
00:50:36,209 --> 00:50:39,143
Ceres is actually
a really wet world.
900
00:50:39,209 --> 00:50:40,986
We thought it was just rock,
901
00:50:41,010 --> 00:50:46,243
but instead, Ceres is rich in
water, ammonia, and carbon.
902
00:50:50,410 --> 00:50:53,143
These chemicals
are essential for life.
903
00:50:53,209 --> 00:50:57,143
Analysis of other asteroids
904
00:50:57,209 --> 00:51:01,043
found lots of
this volatile material.
905
00:51:01,143 --> 00:51:04,643
This is surprising,
because this close in,
906
00:51:04,710 --> 00:51:07,343
the Sun should have
vaporized them.
907
00:51:09,109 --> 00:51:11,285
They could not have formed in
the asteroid belt, because
908
00:51:11,309 --> 00:51:13,786
temperatures were way too high
for those materials...
909
00:51:13,810 --> 00:51:16,143
Water, ammonia...
To be able to condense.
910
00:51:16,209 --> 00:51:19,309
They must have formed in
the outer solar system and then
911
00:51:19,410 --> 00:51:22,209
been transported
to the inner solar system.
912
00:51:24,843 --> 00:51:28,510
A 2019 study discovered
evidence of a storm of
913
00:51:28,610 --> 00:51:34,610
icy objects raining inwards
around 4.48 billion years ago.
914
00:51:34,710 --> 00:51:37,243
At the same time, the giant gas
915
00:51:37,309 --> 00:51:40,443
planets were tearing
through the outer solar system.
916
00:51:41,610 --> 00:51:44,610
As Jupiter and Saturn,
Uranus and Neptune,
917
00:51:44,710 --> 00:51:47,309
are migrating back outwards in
the solar system,
918
00:51:47,410 --> 00:51:51,185
they're excavating a whole
slew of icy planetesimals,
919
00:51:51,209 --> 00:51:54,243
like a like a snowplow bursting
through a snowdrift,
920
00:51:54,309 --> 00:51:56,443
scattering these things all
through the solar system.
921
00:51:59,710 --> 00:52:01,643
The outer planets
hurl millions of
922
00:52:01,710 --> 00:52:06,343
icy objects in towards
their Don, the Sun.
923
00:52:08,010 --> 00:52:13,043
Some, like Ceres,
stop in the asteroid belt.
924
00:52:15,109 --> 00:52:19,010
Others continue and smash
into the inner planets,
925
00:52:22,143 --> 00:52:23,443
including Earth.
926
00:52:26,010 --> 00:52:30,643
We are being rained down on by
giant asteroids, comets.
927
00:52:30,710 --> 00:52:33,143
The entire surface of
the Earth is molten again.
928
00:52:33,209 --> 00:52:35,143
I mean, it is a rain of
the largest
929
00:52:35,209 --> 00:52:38,786
objects you can imagine onto
the surface of the Earth.
930
00:52:38,810 --> 00:52:41,143
Everything just would have
been completely smashed
931
00:52:41,209 --> 00:52:42,309
to pieces.
932
00:52:42,410 --> 00:52:45,343
Imagine something like
the dinosaur-killing impact
933
00:52:45,410 --> 00:52:46,810
happening once a month.
934
00:52:48,143 --> 00:52:51,610
The onslaught lasts
for 30 million years.
935
00:52:54,610 --> 00:52:56,910
It pulverizes
the Earth's surface
936
00:52:59,309 --> 00:53:02,043
but brings fresh chemicals
to replace
937
00:53:02,143 --> 00:53:04,543
material blasted away
by the Sun.
938
00:53:06,309 --> 00:53:09,085
All of these asteroids and
comets raining down on Earth
939
00:53:09,109 --> 00:53:11,710
of course are causing massive
amounts of destruction
940
00:53:11,810 --> 00:53:12,787
but they're bringing
941
00:53:12,811 --> 00:53:14,710
the building blocks
of life, as well.
942
00:53:14,810 --> 00:53:17,710
The carbon-based molecules
that make us up, the water that
943
00:53:17,810 --> 00:53:19,610
every bit of life
on Earth needs,
944
00:53:19,710 --> 00:53:22,209
all of the conditions
necessary for life
945
00:53:22,309 --> 00:53:24,410
were brought by the bombardment.
946
00:53:24,510 --> 00:53:28,610
If that chaotic bombardment
hadn't happened, it's just
947
00:53:28,710 --> 00:53:31,143
possible that we wouldn't be
here today.
948
00:53:31,209 --> 00:53:34,586
Even though some of our
mob family now live in
949
00:53:34,610 --> 00:53:36,543
the outer reaches
of the solar system,
950
00:53:36,610 --> 00:53:38,486
the family ties to the planets
951
00:53:38,510 --> 00:53:41,643
in the inner regions are
still strong.
952
00:53:41,710 --> 00:53:44,043
The distances between all of
953
00:53:44,143 --> 00:53:46,410
the planets in our solar
system are large.
954
00:53:46,510 --> 00:53:47,886
You get a sense of that
955
00:53:47,910 --> 00:53:50,043
if you go into the night sky,
and Jupiter and Saturn
956
00:53:50,143 --> 00:53:51,343
are pinpricks of light,
957
00:53:51,410 --> 00:53:54,543
but really, they're all
interconnected in a very
958
00:53:54,610 --> 00:53:56,443
complex way... gravity has this
959
00:53:56,510 --> 00:54:00,910
huge effect and can go over
long distances.
960
00:54:02,143 --> 00:54:04,753
The solar system
has this huge, violent past
961
00:54:04,777 --> 00:54:07,777
as these giants have
moved and interacted.
962
00:54:09,010 --> 00:54:11,586
It's really remarkable how
interconnected
963
00:54:11,610 --> 00:54:14,209
all these planetary
bodies really are,
964
00:54:14,309 --> 00:54:16,410
even though we think of them
as very separate.
965
00:54:19,510 --> 00:54:21,753
This interaction
between planets,
966
00:54:21,777 --> 00:54:23,710
billions of miles apart,
967
00:54:23,810 --> 00:54:26,343
transformed
the inner solar system
968
00:54:26,410 --> 00:54:28,209
and primed Earth for life.
969
00:54:30,010 --> 00:54:33,710
But our planet was
still uninhabitable.
970
00:54:36,209 --> 00:54:37,956
The early Earth,
right after the bombardment,
971
00:54:38,010 --> 00:54:40,410
would have been
a complete hellscape,
972
00:54:40,510 --> 00:54:43,710
and it would have been
really hot magma everywhere.
973
00:54:43,810 --> 00:54:47,943
Big impact craters with impact
melt all across the floors...
974
00:54:48,043 --> 00:54:49,777
It would have
been unrecognizable.
975
00:54:50,810 --> 00:54:52,843
Not only was it incredibly hot,
976
00:54:52,910 --> 00:54:55,943
but it also didn't have
an atmosphere, and at that time,
977
00:54:56,043 --> 00:54:58,586
there was no liquid water
on the surface yet.
978
00:54:58,610 --> 00:55:02,043
Early Earth could not
have supported life.
979
00:55:02,109 --> 00:55:03,910
For life to start,
980
00:55:04,010 --> 00:55:09,143
Earth must cool down
and build a new atmosphere.
981
00:55:09,209 --> 00:55:12,143
The Earth developed its second
atmosphere using materials
982
00:55:12,209 --> 00:55:14,143
delivered by
the great bombardment.
983
00:55:14,209 --> 00:55:16,410
All of these volatiles,
like water
984
00:55:16,510 --> 00:55:19,643
and carbon organic materials
were incorporated
985
00:55:19,710 --> 00:55:22,085
into the Earth's crust,
and then,
986
00:55:22,109 --> 00:55:23,586
volcanoes were able to outgas
987
00:55:23,610 --> 00:55:26,986
all of these materials, forming
a very thick layer of gas.
988
00:55:27,010 --> 00:55:30,143
This new atmosphere had
a composition that was mostly
989
00:55:30,209 --> 00:55:33,843
water vapor, carbon dioxide,
and nitrogen.
990
00:55:33,910 --> 00:55:36,386
Over the next 30 million years,
991
00:55:36,410 --> 00:55:40,410
Earth cools...
A solid surface forms.
992
00:55:42,209 --> 00:55:44,486
As the planet is cooling,
the water vapor
993
00:55:44,510 --> 00:55:46,843
in the atmosphere
is going to be raining out.
994
00:55:46,910 --> 00:55:50,143
That's gonna form
pools of liquid water
995
00:55:50,209 --> 00:55:51,321
on the surface of the Earth.
996
00:55:53,610 --> 00:55:55,143
The earliest
evidence for liquid water
997
00:55:55,209 --> 00:55:57,910
on Earth was
4.3 billion years ago.
998
00:55:58,010 --> 00:56:00,486
Remember, that's just
200 million years after
999
00:56:00,510 --> 00:56:02,777
its formation,
which is really fast.
1000
00:56:04,309 --> 00:56:07,643
Trillions of gallons
of water rain down.
1001
00:56:08,810 --> 00:56:12,043
Torrential rains for, I mean,
you know, imagine monsoon rains
1002
00:56:12,143 --> 00:56:15,243
for, you know, tens and tens
of thousands of years.
1003
00:56:19,109 --> 00:56:20,710
All this water would have rained
1004
00:56:20,810 --> 00:56:21,787
onto the surface, rained,
1005
00:56:21,811 --> 00:56:25,043
rained, and eventually
filled up our oceans.
1006
00:56:27,510 --> 00:56:30,209
The oceans pull
life-forming chemicals from
1007
00:56:30,309 --> 00:56:35,109
the rocks and the atmosphere,
creating the primordial soup.
1008
00:56:36,543 --> 00:56:38,510
Life can begin.
1009
00:56:39,777 --> 00:56:42,285
We used to be so
disconnected from each other,
1010
00:56:42,309 --> 00:56:44,610
each planet just living
entirely separately.
1011
00:56:44,710 --> 00:56:46,710
Now, we know things mix around.
1012
00:56:46,810 --> 00:56:49,543
Now we know that probably
the building blocks of
1013
00:56:49,610 --> 00:56:51,710
life itself
and the water in my body
1014
00:56:51,810 --> 00:56:53,643
actually came from
the outer solar system.
1015
00:56:53,710 --> 00:56:55,543
I like that.
1016
00:56:56,710 --> 00:56:59,443
A series of
interconnecting and often
1017
00:56:59,510 --> 00:57:01,486
violent incidents
going right back
1018
00:57:01,510 --> 00:57:05,309
to the start of the solar
system led to our existence.
1019
00:57:05,410 --> 00:57:09,753
If you look at what the
solar system has been through,
1020
00:57:09,777 --> 00:57:13,143
what has to happen for life
to happen.
1021
00:57:13,209 --> 00:57:16,043
When you add all of those
things up, we shouldn't exist.
1022
00:57:16,109 --> 00:57:19,143
We just shouldn't be here.
The chances are so, so slim.
1023
00:57:19,209 --> 00:57:21,043
And yet here we are.
1024
00:57:22,309 --> 00:57:24,710
The Earth has managed to
survive a lot of the nonsense
1025
00:57:24,810 --> 00:57:26,543
the solar system
has thrown at it,
1026
00:57:26,610 --> 00:57:29,209
and some of that is probably
just luck of the draw.
1027
00:57:29,309 --> 00:57:31,486
So I think even
on our worst days,
1028
00:57:31,510 --> 00:57:34,285
we should remember that we're
pretty lucky just to be here.
1029
00:57:34,309 --> 00:57:38,410
Earth won the cosmic
game of chance,
1030
00:57:39,710 --> 00:57:43,143
but were the other
Mafioso children as lucky?
1031
00:57:43,209 --> 00:57:44,943
Did Mars and Venus
1032
00:57:45,043 --> 00:57:49,410
also develop environments
capable of supporting life?
1033
00:57:59,543 --> 00:58:03,085
200 million years
after the birth of the Sun,
1034
00:58:03,109 --> 00:58:05,109
the mafia family prospers.
1035
00:58:07,043 --> 00:58:09,543
The inner planets have
the building blocks of
1036
00:58:09,610 --> 00:58:12,309
life thrown in from
the outer solar system.
1037
00:58:15,209 --> 00:58:18,143
So, in theory,
they could be habitable.
1038
00:58:23,410 --> 00:58:28,643
But when the Russian probe
Venera landed on Venus in 1970,
1039
00:58:28,710 --> 00:58:31,343
it found a scorching,
hostile world.
1040
00:58:33,010 --> 00:58:35,209
The conditions
on Venus are crazy.
1041
00:58:35,309 --> 00:58:38,943
The temperature on the surface
is over 800 degrees Fahrenheit,
1042
00:58:39,043 --> 00:58:41,185
so it's hot enough to melt lead.
1043
00:58:41,209 --> 00:58:43,943
The first probes that
landed on Venus functioned for
1044
00:58:44,043 --> 00:58:45,410
a little while,
and then they were
1045
00:58:45,510 --> 00:58:47,010
crushed like a tin can
and melted.
1046
00:58:48,777 --> 00:58:52,810
It has a huge, crushing
atmospheric pressure,
1047
00:58:52,910 --> 00:58:55,643
which is 90 times that on
the Earth's surface,
1048
00:58:55,710 --> 00:58:58,309
and that's entirely
carbon dioxide.
1049
00:59:00,943 --> 00:59:03,410
And it gets worse still,
because gasses in
1050
00:59:03,510 --> 00:59:05,209
the atmosphere have combined
1051
00:59:05,309 --> 00:59:08,386
to make really this concentrated
solution of gasses.
1052
00:59:08,410 --> 00:59:10,386
So you've got this noxious,
1053
00:59:10,410 --> 00:59:14,309
acidic, corrosive environment
coupled with very, very
1054
00:59:14,410 --> 00:59:16,143
high temperatures.
1055
00:59:16,209 --> 00:59:18,243
Life as we know it
could not survive
1056
00:59:18,309 --> 00:59:20,510
on the surface of Venus
as it is today.
1057
00:59:25,309 --> 00:59:29,243
New climate models suggest
that four billion years ago,
1058
00:59:29,309 --> 00:59:34,043
Venus was a very different
planet to the one we see today.
1059
00:59:34,143 --> 00:59:38,543
These models suggest that, in
the past, Venus had actually
1060
00:59:38,610 --> 00:59:42,043
a cooler surface temperature
and had a better composition
1061
00:59:42,109 --> 00:59:43,343
for habitability.
1062
00:59:45,610 --> 00:59:49,043
We think it once had a much
thinner atmosphere, much more
1063
00:59:49,109 --> 00:59:51,043
like Earth's atmosphere today.
1064
00:59:51,143 --> 00:59:55,309
It would have had a climate,
which was much, much cooler,
1065
00:59:55,410 --> 00:59:59,285
and therefore, even
the possibility of liquid water
1066
00:59:59,309 --> 01:00:02,810
on the surface...
Maybe Venus had oceans
1067
01:00:02,877 --> 01:00:05,610
in the way that we find
on Earth still today.
1068
01:00:07,410 --> 01:00:09,886
It even makes sense that Venus
would be similar to Earth,
1069
01:00:09,910 --> 01:00:11,986
because it formed out
of basically
1070
01:00:12,010 --> 01:00:14,943
the same materials, close to
the same location from the Sun,
1071
01:00:15,043 --> 01:00:17,610
and ended up being even
almost the same size.
1072
01:00:19,243 --> 01:00:22,386
Really, we are twin planets.
1073
01:00:22,410 --> 01:00:26,143
The barrage of icy objects
1074
01:00:26,209 --> 01:00:30,143
from the outer solar system that
struck Earth also hit Venus.
1075
01:00:31,309 --> 01:00:34,510
Just like Earth,
Venus got a whole bunch
1076
01:00:34,610 --> 01:00:37,753
of volatiles from bombardments,
and those in turn were
1077
01:00:37,777 --> 01:00:41,185
recycled and produced a very
nice atmosphere
1078
01:00:41,209 --> 01:00:44,143
and allowed water to exist
on the surface as a liquid.
1079
01:00:47,043 --> 01:00:51,243
These early conditions on
Venus could have provided
1080
01:00:51,309 --> 01:00:53,209
a habitat,
1081
01:00:53,309 --> 01:00:56,810
the right sort of conditions
for life to have got started.
1082
01:00:56,910 --> 01:00:59,085
What about Mars?
1083
01:00:59,109 --> 01:01:01,710
Was it also habitable?
1084
01:01:01,810 --> 01:01:03,853
Looking at it today, all we see
1085
01:01:03,877 --> 01:01:06,486
is a frozen, barren wasteland.
1086
01:01:06,510 --> 01:01:09,443
Part of the reason it's so
cold is it's further away
1087
01:01:09,510 --> 01:01:12,085
from the Sun, and it doesn't
have a very thick atmosphere.
1088
01:01:12,109 --> 01:01:14,410
So it's very hard
for it to retain heat.
1089
01:01:14,510 --> 01:01:17,710
It also has extremely
low atmospheric pressure,
1090
01:01:17,810 --> 01:01:20,486
which means that any liquid
water on the surface would just
1091
01:01:20,510 --> 01:01:23,443
boil away, and any current water
1092
01:01:23,510 --> 01:01:26,510
that's on the planet
is locked up in ice.
1093
01:01:27,510 --> 01:01:30,810
However, recent surveys
of Mars reveal
1094
01:01:30,877 --> 01:01:35,853
a very different planet, once
capable of supporting life.
1095
01:01:35,877 --> 01:01:37,943
As you look across
the landscape of Mars,
1096
01:01:38,043 --> 01:01:41,209
you can see these physical
features that give us hints
1097
01:01:41,309 --> 01:01:42,810
that water used to exist there,
1098
01:01:42,910 --> 01:01:46,309
like dried lake beds
and riverbeds.
1099
01:01:46,410 --> 01:01:49,510
We see abundant
evidence of river channels,
1100
01:01:49,610 --> 01:01:52,209
drainages all across
the landscape.
1101
01:01:52,309 --> 01:01:55,143
The best way, I think the only
way to form these is
1102
01:01:55,209 --> 01:01:56,343
by rainfall.
1103
01:01:56,410 --> 01:01:59,443
There had to have been clouds
and rain in Mars's past.
1104
01:01:59,510 --> 01:02:02,810
And there's also sediments
and mineral deposits that could
1105
01:02:02,910 --> 01:02:05,910
only form in the presence of
liquid water.
1106
01:02:08,109 --> 01:02:11,486
We calculate that Mars
once had five million
1107
01:02:11,510 --> 01:02:14,386
cubic miles of liquid water
on the surface.
1108
01:02:14,410 --> 01:02:17,853
That's enough for an ocean
1109
01:02:17,877 --> 01:02:19,943
bigger than the Earth's
Arctic Ocean.
1110
01:02:20,043 --> 01:02:22,586
So we think that Mars had
an ocean
1111
01:02:22,610 --> 01:02:24,710
in its northern hemisphere.
1112
01:02:27,109 --> 01:02:29,586
To have oceans,
1113
01:02:29,610 --> 01:02:32,510
Mars must have had
a thick atmosphere.
1114
01:02:34,410 --> 01:02:36,309
And recently, a space probe
1115
01:02:36,410 --> 01:02:39,877
orbiting the red planet
found evidence.
1116
01:02:42,043 --> 01:02:43,710
The MAVEN mission revealed that
1117
01:02:43,777 --> 01:02:46,586
Mars is losing its
atmosphere rapidly.
1118
01:02:46,610 --> 01:02:48,386
I mean, this is
something like a quarter pound
1119
01:02:48,410 --> 01:02:51,243
a second of atmosphere
being stripped away
1120
01:02:51,309 --> 01:02:52,510
by the solar wind.
1121
01:02:52,610 --> 01:02:55,710
We can take those MAVEN loss
rates for Mars's atmosphere
1122
01:02:55,777 --> 01:02:57,043
and extrapolate back in time,
1123
01:02:57,143 --> 01:02:59,986
and we can see that Mars had
an atmosphere as thick as
1124
01:03:00,010 --> 01:03:01,986
Earth's in the past.
1125
01:03:02,010 --> 01:03:03,710
With a thicker atmosphere,
Mars would
1126
01:03:03,777 --> 01:03:07,209
have been able to retain heat
much more effectively
1127
01:03:07,309 --> 01:03:09,254
and would have had increased
atmospheric pressure,
1128
01:03:09,309 --> 01:03:11,643
which would have allowed
liquid water to persist on
1129
01:03:11,710 --> 01:03:12,610
the surface.
1130
01:03:12,710 --> 01:03:14,410
In the past,
Mars would have been just
1131
01:03:14,510 --> 01:03:18,486
a beautiful landscape filled
with running rivers and lakes,
1132
01:03:18,510 --> 01:03:21,085
and that water could have
potentially sustained
1133
01:03:21,109 --> 01:03:22,410
ancient life.
1134
01:03:25,143 --> 01:03:28,243
All of the observations that
we have of Mars to date
1135
01:03:28,309 --> 01:03:31,643
just tell us that it was
absolutely a habitable world.
1136
01:03:31,710 --> 01:03:35,886
So now we have
an Earth that had kind of
1137
01:03:35,910 --> 01:03:38,209
settled down after the heavy
bombardment of Venus
1138
01:03:38,309 --> 01:03:39,943
that might have
water on the surface
1139
01:03:40,043 --> 01:03:41,810
and a thinner atmosphere
and Mars, with
1140
01:03:41,877 --> 01:03:43,663
a thicker atmosphere
and water on the surface,
1141
01:03:43,710 --> 01:03:47,486
water on all three surfaces...
Maybe all three were right
1142
01:03:47,510 --> 01:03:48,710
for life.
1143
01:03:48,777 --> 01:03:51,710
It's actually remarkable to
think that all three of
1144
01:03:51,777 --> 01:03:54,943
these planets could have been
habitable at the same time.
1145
01:03:56,109 --> 01:03:59,143
But this golden age
of habitability
1146
01:03:59,209 --> 01:04:00,243
is short-lived.
1147
01:04:02,410 --> 01:04:05,043
Another battle erupts
between the planets
1148
01:04:05,109 --> 01:04:08,085
and their Don, the Sun.
1149
01:04:08,109 --> 01:04:12,410
Venus and Mars suffers
serious collateral damage.
1150
01:04:24,643 --> 01:04:26,410
Four billion years ago,
1151
01:04:26,510 --> 01:04:30,010
the mob family,
the solar system, is thriving.
1152
01:04:32,543 --> 01:04:35,343
The children, Earth, Mars
and Venus,
1153
01:04:35,410 --> 01:04:38,209
have the conditions to
sustain life.
1154
01:04:44,343 --> 01:04:47,143
2020... scientists investigate
1155
01:04:47,209 --> 01:04:49,610
how Mars became uninhabitable.
1156
01:04:51,810 --> 01:04:55,309
They detect faint magnetic
traces coming from
1157
01:04:55,410 --> 01:04:58,877
lava spewed out by ancient
volcanic eruptions.
1158
01:05:02,043 --> 01:05:07,010
The magnetic lava on Mars
tells us that when that lava
1159
01:05:07,076 --> 01:05:12,010
was molten, there was a strong
global magnetic field
1160
01:05:12,076 --> 01:05:13,343
on that planet.
1161
01:05:15,109 --> 01:05:18,185
Dating the rocks
tells us that Mars's
1162
01:05:18,209 --> 01:05:23,977
magnetic field was active
4.5 billion years ago.
1163
01:05:24,043 --> 01:05:28,043
Having a magnetic field really
helps a planet retain
1164
01:05:28,109 --> 01:05:30,285
its atmosphere, and that's just
because a magnetic field
1165
01:05:30,309 --> 01:05:33,543
protects the planet's atmosphere
from incoming radiation.
1166
01:05:33,610 --> 01:05:36,309
Solar wind, cosmic rays,
you name it.
1167
01:05:43,209 --> 01:05:46,043
On Earth, liquid iron
churning around
1168
01:05:46,109 --> 01:05:49,710
the hot molten core generates
a magnetic field.
1169
01:05:51,309 --> 01:05:56,076
The younger Mars
would have still had a much
1170
01:05:56,143 --> 01:05:59,810
hotter core, with churning
convection currents in
1171
01:05:59,910 --> 01:06:01,176
its interior,
1172
01:06:01,209 --> 01:06:05,643
and these would have generated
a global magnetic field in
1173
01:06:05,710 --> 01:06:09,285
exactly the same way the Earth
creates its magnetic field.
1174
01:06:09,309 --> 01:06:15,143
Mars couldn't maintain
its magnetic field,
1175
01:06:15,209 --> 01:06:17,753
because Jupiter's violent
assault on the inner
1176
01:06:17,777 --> 01:06:20,910
solar system stole
the red planet's lunch,
1177
01:06:22,343 --> 01:06:25,510
Jupiter migrated in
about where Mars is today.
1178
01:06:25,610 --> 01:06:27,810
So that means that most of
the material
1179
01:06:27,877 --> 01:06:30,285
was actually swallowed up by
the gravity of Jupiter.
1180
01:06:30,309 --> 01:06:33,185
So Mars just got unlucky.
1181
01:06:33,209 --> 01:06:36,710
Small planets lose heat faster.
1182
01:06:36,777 --> 01:06:39,410
Tiny Mars cooled down.
1183
01:06:39,510 --> 01:06:42,185
And so as Mars's core cooled,
1184
01:06:42,209 --> 01:06:45,243
the convection in that core
would have slowed down, to
1185
01:06:45,309 --> 01:06:47,853
the point where no magnetic
field would be generated.
1186
01:06:47,877 --> 01:06:50,443
Once the magnetic field
at Mars is shut off,
1187
01:06:50,510 --> 01:06:53,309
well, that's the end of the
protection for the atmosphere.
1188
01:06:55,910 --> 01:06:58,643
3.7 billion years ago,
1189
01:06:58,710 --> 01:07:01,910
the Sun attacks
the defenseless Mars.
1190
01:07:02,010 --> 01:07:06,810
The solar wind just
bombards it and strips it
1191
01:07:06,877 --> 01:07:09,243
away of the atmosphere
very quickly over time.
1192
01:07:10,410 --> 01:07:11,977
Without its thermal blanket,
1193
01:07:12,043 --> 01:07:15,810
Mars's surface freezes,
and the atmospheric
1194
01:07:15,910 --> 01:07:18,510
pressure plummets.
1195
01:07:18,610 --> 01:07:23,243
As the atmospheric pressure
drops, surface water
1196
01:07:23,309 --> 01:07:26,510
gradually evaporates
or even boils away.
1197
01:07:32,643 --> 01:07:35,710
Venus also suffered
a climate catastrophe.
1198
01:07:37,777 --> 01:07:40,043
We find clues on its surface.
1199
01:07:43,543 --> 01:07:46,977
Like all planetary-sized
bodies in the solar system,
1200
01:07:47,043 --> 01:07:49,010
Venus has impact craters on it
1201
01:07:49,076 --> 01:07:51,010
from asteroids smacking into it,
1202
01:07:51,076 --> 01:07:54,853
but there aren't that many,
which is a little odd.
1203
01:07:54,877 --> 01:07:56,085
They're not damaged
1204
01:07:56,109 --> 01:07:58,710
like the craters we see
on other worlds.
1205
01:07:58,810 --> 01:08:02,810
They look pristine,
as if nothing has modified them,
1206
01:08:02,910 --> 01:08:04,386
as if they happened yesterday.
1207
01:08:04,410 --> 01:08:07,285
So that suggests
these craters and the surface
1208
01:08:07,309 --> 01:08:09,443
on which they reside
are both very young.
1209
01:08:11,043 --> 01:08:13,309
There are several
theories suggesting that
1210
01:08:13,410 --> 01:08:14,810
volcanic eruptions
1211
01:08:14,910 --> 01:08:18,143
resurfaced the planet around
500 million years ago.
1212
01:08:20,710 --> 01:08:23,586
One idea is that Venus has
a very thick crust,
1213
01:08:23,610 --> 01:08:26,343
and it doesn't move around in
plates like Earth's does.
1214
01:08:26,410 --> 01:08:29,386
So it's just a lid over
the planet, and eventually,
1215
01:08:29,410 --> 01:08:31,209
the pressure builds up
and builds up
1216
01:08:31,309 --> 01:08:33,710
and builds up until it...
Boom, lets out all at once.
1217
01:08:39,710 --> 01:08:43,243
A catastrophic event
that overturned
1218
01:08:43,309 --> 01:08:46,910
the entire crust of Venus
and resurfaced it.
1219
01:08:48,343 --> 01:08:50,085
An alternate theory suggests
1220
01:08:50,109 --> 01:08:53,343
the resurfacing happened over
millions of years.
1221
01:08:54,610 --> 01:08:57,143
A series of large
volcanic eruptions
1222
01:08:57,209 --> 01:08:59,309
that would have completely
resurfaced the planet.
1223
01:09:02,810 --> 01:09:05,343
Imagine watching
this event on Venus... I mean,
1224
01:09:05,410 --> 01:09:08,443
the overturn of an entire crust?
1225
01:09:08,510 --> 01:09:10,309
That's just completely
awe-inspiring.
1226
01:09:11,910 --> 01:09:15,209
Volcanic events
release huge amounts of gas.
1227
01:09:19,010 --> 01:09:21,510
Icelandic volcano,
Eyjafjallajokull,
1228
01:09:21,610 --> 01:09:26,810
blasts out up to 300,000 tons
of carbon dioxide every day.
1229
01:09:29,209 --> 01:09:33,143
Venus's planet-wide volcanism
would have been off the charts.
1230
01:09:35,410 --> 01:09:41,753
Such a huge worldwide bout of
volcanic activity would release
1231
01:09:41,777 --> 01:09:46,910
huge amounts of carbon dioxide
in the Venusian atmosphere.
1232
01:09:46,977 --> 01:09:50,710
Scientists think
this enormous release of gas
1233
01:09:50,777 --> 01:09:54,710
may have triggered
the Venusian climate change.
1234
01:09:54,777 --> 01:09:57,185
Carbon dioxide
built up in Venus's
1235
01:09:57,209 --> 01:10:01,243
atmosphere, trapping
heat from the Sun.
1236
01:10:01,309 --> 01:10:04,143
As soon as the climate
on Venus started to warm up
1237
01:10:04,209 --> 01:10:06,977
a little,
there's greater evaporation
1238
01:10:07,043 --> 01:10:10,586
coming off the oceans,
and that water vapor
1239
01:10:10,610 --> 01:10:14,076
in the atmosphere
is itself a greenhouse gas.
1240
01:10:14,143 --> 01:10:16,309
The climate gets even warmer.
1241
01:10:18,243 --> 01:10:21,810
Venus reaches
880 degrees Fahrenheit.
1242
01:10:25,309 --> 01:10:28,877
Any chance for life broils away.
1243
01:10:33,710 --> 01:10:36,853
The Earth also faces
a searing hot future
1244
01:10:36,877 --> 01:10:39,243
when the aging Godfather,
1245
01:10:39,309 --> 01:10:44,209
the Sun, bloats up and attacks
his family once again,
1246
01:10:44,309 --> 01:10:49,309
transforming into a lethal
weapon of mass destruction.
1247
01:11:02,109 --> 01:11:05,043
For the last four billion
years, our mob family,
1248
01:11:05,109 --> 01:11:07,710
the solar system,
lived in harmony,
1249
01:11:07,777 --> 01:11:11,152
but nothing lasts forever.
1250
01:11:11,176 --> 01:11:14,152
The godfather, the Sun,
1251
01:11:14,176 --> 01:11:17,386
will grow old, fat, and mean.
1252
01:11:17,410 --> 01:11:21,285
Stars like the Sun
only have enough
1253
01:11:21,309 --> 01:11:24,285
hydrogen to fuse for about
10 billion years.
1254
01:11:24,309 --> 01:11:27,510
So that means that
in about five billion years,
1255
01:11:27,610 --> 01:11:31,610
the Sun will actually
run out of hydrogen.
1256
01:11:33,810 --> 01:11:37,043
With no hydrogen
fuel left, fusion stops.
1257
01:11:38,143 --> 01:11:42,443
The core collapses
and reignites, fusing helium.
1258
01:11:52,910 --> 01:11:55,977
The energy released by
all of this fusion causes
1259
01:11:56,043 --> 01:11:59,977
the star to balloon outwards
and become a red giant.
1260
01:12:02,410 --> 01:12:05,643
The red giant is like
a bitter old gangster.
1261
01:12:07,209 --> 01:12:10,710
Bloated and aggressive,
it attacks the inner planets.
1262
01:12:14,610 --> 01:12:16,343
Mercury and Venus
are gonna be engulfed
1263
01:12:16,410 --> 01:12:18,543
by the Sun as it becomes
a red giant.
1264
01:12:19,977 --> 01:12:21,710
It burns up both planets.
1265
01:12:23,043 --> 01:12:25,109
Next in line, Earth.
1266
01:12:26,710 --> 01:12:30,443
Then the universe
throws us a lifeline.
1267
01:12:30,510 --> 01:12:35,386
As the Sun expands outward, as
it enters its red giant phase,
1268
01:12:35,410 --> 01:12:38,309
it's actually going to be
losing mass.
1269
01:12:42,010 --> 01:12:44,109
The red giant blows off gas.
1270
01:12:45,643 --> 01:12:48,853
And as it loses mass,
its gravity is weakening.
1271
01:12:48,877 --> 01:12:51,543
So this means that
the Sun's grip on
1272
01:12:51,610 --> 01:12:54,285
the planets that orbit it
is gonna be weakening.
1273
01:12:54,309 --> 01:12:57,586
And so they sort of start
moving away from the Sun.
1274
01:12:57,610 --> 01:13:00,185
It's almost like they're
running away from the heat.
1275
01:13:00,209 --> 01:13:03,343
If you can't stand the heat,
get out of the solar system.
1276
01:13:05,309 --> 01:13:08,810
Can Earth and Mars outrun
the expanding red giant?
1277
01:13:10,010 --> 01:13:12,410
So it's a race, right?
Who is going to get
1278
01:13:12,510 --> 01:13:16,510
far enough from the Sun to
escape being engulfed by it?
1279
01:13:18,810 --> 01:13:21,309
The eventual fate
of the Earth is not clear.
1280
01:13:23,043 --> 01:13:26,143
It's possible that the Earth
will be completely swallowed up
1281
01:13:26,209 --> 01:13:27,810
by the Sun's atmosphere,
1282
01:13:27,877 --> 01:13:31,410
its new, bloated,
red atmosphere.
1283
01:13:36,510 --> 01:13:40,185
Even if the Earth escapes
being directly
1284
01:13:40,209 --> 01:13:41,510
engulfed by the Sun,
1285
01:13:41,610 --> 01:13:45,109
it's still not a good day for
our planet, because the Sun is
1286
01:13:45,176 --> 01:13:47,543
gonna be really, really close.
1287
01:13:47,610 --> 01:13:50,753
So imagine basically
something red-hot, glowing,
1288
01:13:50,777 --> 01:13:52,043
covering the sky.
1289
01:13:52,109 --> 01:13:54,152
The earth will be molten,
and in fact, a lot of it
1290
01:13:54,176 --> 01:13:55,610
will vaporize.
1291
01:13:55,710 --> 01:13:58,076
So it's not like you're gonna
want to be here anyway.
1292
01:13:59,209 --> 01:14:00,710
As I look at this scenario,
1293
01:14:00,777 --> 01:14:04,176
what's clear is that life
isn't gonna make it on Earth.
1294
01:14:09,010 --> 01:14:12,977
Mars had a head start and
escapes complete destruction.
1295
01:14:14,109 --> 01:14:16,143
It'll be cooked, I mean,
it'll be a molten planet,
1296
01:14:16,209 --> 01:14:17,510
but it'll still be there.
1297
01:14:21,777 --> 01:14:24,285
The aging Don wipes out life in
1298
01:14:24,309 --> 01:14:30,810
the inner solar system but may
help it survive elsewhere.
1299
01:14:31,910 --> 01:14:34,143
The sun's red giant phase
may initially bring
1300
01:14:34,209 --> 01:14:36,610
new opportunities for life in
the outer solar system.
1301
01:14:38,510 --> 01:14:42,285
Right now, the outer
solar system is locked in ice,
1302
01:14:42,309 --> 01:14:43,586
it's way too cold,
1303
01:14:43,610 --> 01:14:46,753
but when our sun becomes a red
giant, it will become much,
1304
01:14:46,777 --> 01:14:47,610
much brighter.
1305
01:14:47,710 --> 01:14:50,510
It will warm up
the outer system.
1306
01:14:53,410 --> 01:14:57,643
And transform the gas
giant's icy moons.
1307
01:14:59,610 --> 01:15:01,810
Europa and Enceladus,
that orbit Jupiter
1308
01:15:01,877 --> 01:15:04,977
and Saturn respectively, are
currently frozen worlds.
1309
01:15:05,043 --> 01:15:07,410
They have icy crusts
and are believed
1310
01:15:07,510 --> 01:15:09,910
to have liquid oceans
below those crusts.
1311
01:15:18,510 --> 01:15:21,285
Scientists believe
that these subsurface oceans
1312
01:15:21,309 --> 01:15:23,753
may harbor life.
1313
01:15:23,777 --> 01:15:26,410
As the temperature increases,
1314
01:15:26,510 --> 01:15:28,810
their frozen exteriors are
gonna be thawed,
1315
01:15:28,910 --> 01:15:30,910
and they'll become
entirely ocean worlds.
1316
01:15:35,810 --> 01:15:38,285
Any life forms
already evolving in their oceans
1317
01:15:38,309 --> 01:15:40,777
will have a whole new world of
possibility open to them.
1318
01:15:42,510 --> 01:15:44,076
Or if life isn't there yet,
1319
01:15:44,143 --> 01:15:46,309
then it would certainly have
a chance to evolve.
1320
01:15:46,410 --> 01:15:48,710
We may have explosions of life
1321
01:15:48,810 --> 01:15:51,343
on these other outer
solar system bodies.
1322
01:15:53,910 --> 01:15:57,176
But this burst of
new life may be short-lived.
1323
01:15:58,510 --> 01:16:01,109
Even though these ocean worlds
may seem like a great
1324
01:16:01,176 --> 01:16:04,010
place to move to after
the inner solar system
1325
01:16:04,076 --> 01:16:06,643
is engulfed,
I would not start packing yet.
1326
01:16:12,610 --> 01:16:17,643
The red giant will grow to
over 250 times its current size.
1327
01:16:18,877 --> 01:16:21,243
As the Sun continues to expand,
1328
01:16:21,309 --> 01:16:24,443
these new ocean worlds
will start getting hotter
1329
01:16:24,510 --> 01:16:26,910
and hotter, and eventually,
all of the water will
1330
01:16:26,977 --> 01:16:28,010
evaporate away.
1331
01:16:32,043 --> 01:16:34,010
Any new life dies out,
1332
01:16:37,010 --> 01:16:39,443
but bodies
in the furthest reaches
1333
01:16:39,510 --> 01:16:42,910
of the solar system fare better.
1334
01:16:43,010 --> 01:16:45,010
The key to surviving
the Sun turning
1335
01:16:45,076 --> 01:16:47,143
into a red giant is
basically distance.
1336
01:16:47,209 --> 01:16:49,753
So the farther out
you are from the Sun now,
1337
01:16:49,777 --> 01:16:51,343
the better off you are then.
1338
01:16:53,910 --> 01:16:57,443
The best bet might be
the distant dwarf planets,
1339
01:16:57,510 --> 01:16:58,910
like Pluto.
1340
01:17:01,309 --> 01:17:03,910
So now we have these objects
that might actually
1341
01:17:04,010 --> 01:17:07,076
become the most Earth-like
bodies in the solar system.
1342
01:17:07,143 --> 01:17:09,176
These may be our lifeboats.
1343
01:17:13,910 --> 01:17:16,343
I mean, they won't have
breathable atmospheres,
1344
01:17:16,410 --> 01:17:18,486
and it's not like they're gonna
be great places to live,
1345
01:17:18,510 --> 01:17:21,209
but, you know, the Earth is
gonna be basically toast at
1346
01:17:21,309 --> 01:17:23,977
that point, so, you know,
what choice do you have?
1347
01:17:24,043 --> 01:17:28,243
Humanity may use the warm
outer bodies as stepping stones
1348
01:17:28,309 --> 01:17:30,710
to a new home, because when
1349
01:17:30,777 --> 01:17:33,185
the Godfather's sun
gets very old,
1350
01:17:33,209 --> 01:17:38,309
he becomes frail and unable to
stop other more powerful Dons
1351
01:17:38,410 --> 01:17:41,810
from destroying
the solar system forever.
1352
01:17:55,510 --> 01:17:58,610
Six billion years in the future.
1353
01:17:59,810 --> 01:18:03,910
The aging Godfather's attack
on his children ends.
1354
01:18:06,910 --> 01:18:10,710
The bloated red giant dies,
releasing a burst of energy,
1355
01:18:10,810 --> 01:18:12,910
which blasts the outer regions
1356
01:18:13,010 --> 01:18:16,043
of the star, plus the remains
of the vaporized
1357
01:18:16,109 --> 01:18:18,076
planets, out into space...
1358
01:18:21,309 --> 01:18:24,410
...ready to build new stars
and new planets.
1359
01:18:25,877 --> 01:18:28,610
What's left are veils of
1360
01:18:28,710 --> 01:18:32,209
beautiful colored gas called
a planetary nebula,
1361
01:18:33,276 --> 01:18:35,586
the surviving planets,
1362
01:18:35,610 --> 01:18:40,109
and, at the heart,
the remains of the Sun,
1363
01:18:40,176 --> 01:18:45,043
now nothing
but a burnt-out core.
1364
01:18:46,343 --> 01:18:49,586
We call those leftover cores
from small stars
1365
01:18:49,610 --> 01:18:53,610
white dwarf stars, and they're
much smaller than the Sun.
1366
01:18:54,810 --> 01:18:57,810
The white dwarf will be
about half the Sun's original
1367
01:18:57,877 --> 01:19:02,252
mass and all contained into
the size of the Earth.
1368
01:19:02,276 --> 01:19:05,443
The dense white dwarf
doesn't burn fuel,
1369
01:19:05,510 --> 01:19:07,710
so it can't generate energy.
1370
01:19:09,710 --> 01:19:11,977
The solar system cools.
1371
01:19:13,143 --> 01:19:15,810
We'll start seeing freezing
from the outer solar system
1372
01:19:15,877 --> 01:19:18,977
to the inner solar system...
We'll start with Pluto.
1373
01:19:20,309 --> 01:19:22,643
Then Enceladus around Saturn.
1374
01:19:23,810 --> 01:19:26,076
And then Europa around Jupiter,
1375
01:19:26,143 --> 01:19:27,853
and then finally Mars.
1376
01:19:27,877 --> 01:19:32,643
So, you know, they've already
had any volatiles sent away.
1377
01:19:32,710 --> 01:19:35,386
Their surfaces are now gonna
be metallic and rocky,
1378
01:19:35,410 --> 01:19:39,152
and you're gonna end up with
these very frozen, rocky,
1379
01:19:39,176 --> 01:19:41,285
metallic worlds.
1380
01:19:41,309 --> 01:19:44,252
The near-dead Godfather
1381
01:19:44,276 --> 01:19:46,910
is now a shadow
of his former self.
1382
01:19:48,010 --> 01:19:49,486
And the solar system is at
1383
01:19:49,510 --> 01:19:52,910
the mercy of more powerful
mobster stars.
1384
01:19:53,010 --> 01:19:56,443
The white dwarf of the Sun has
about half the mass
1385
01:19:56,510 --> 01:19:57,487
of the Sun today,
1386
01:19:57,511 --> 01:19:59,643
which means gravity
is half as strong.
1387
01:19:59,710 --> 01:20:02,910
So the planets in their orbits
will move further out.
1388
01:20:05,209 --> 01:20:07,443
These outer planets,
which survived
1389
01:20:07,510 --> 01:20:09,285
the Sun turning
into a red giant,
1390
01:20:09,309 --> 01:20:12,076
their orbits are now much, much
larger than they were before,
1391
01:20:12,143 --> 01:20:15,109
up to about a factor of two.
1392
01:20:15,176 --> 01:20:18,443
That's an issue, because there
are other stars in the galaxy.
1393
01:20:19,610 --> 01:20:23,143
We're part of the Milky Way
Galaxy, and our best estimate
1394
01:20:23,209 --> 01:20:26,910
is that there is something like
100 billion other suns like ours
1395
01:20:27,010 --> 01:20:28,276
orbiting our galaxy.
1396
01:20:29,810 --> 01:20:32,710
Every 20 million years,
something like that,
1397
01:20:32,810 --> 01:20:36,109
one of them will pass by close
enough to affect the orbits
1398
01:20:36,176 --> 01:20:37,410
of these planets.
1399
01:20:40,410 --> 01:20:44,443
So in this distant future,
where our sun is a white dwarf,
1400
01:20:44,510 --> 01:20:47,076
as our orbits are larger
and things are moving slower,
1401
01:20:47,143 --> 01:20:50,309
we're way more susceptible to
the effects of passing stars.
1402
01:20:53,076 --> 01:20:55,543
You can imagine this like
ships passing each other in
1403
01:20:55,610 --> 01:20:58,710
the ocean, where there's one
whizzes by another,
1404
01:20:58,777 --> 01:21:02,586
it creates waves that knock
the other one around.
1405
01:21:02,610 --> 01:21:07,043
Passing stars will give
the planets little nudges,
1406
01:21:07,109 --> 01:21:08,109
little kicks.
1407
01:21:08,143 --> 01:21:13,109
The giant planets will enter
a chaotic phase
1408
01:21:13,176 --> 01:21:15,343
where everything
except for Jupiter will be
1409
01:21:15,410 --> 01:21:16,977
scattered out of
the solar system.
1410
01:21:21,410 --> 01:21:22,643
50 billion years in the future,
1411
01:21:22,710 --> 01:21:27,152
the solar system faces another
ruthless gangster
1412
01:21:27,176 --> 01:21:28,810
out on the make.
1413
01:21:28,910 --> 01:21:31,853
Its gravity is gonna
yank Jupiter away from the Sun
1414
01:21:31,877 --> 01:21:33,910
and fling it out into
interstellar space,
1415
01:21:34,010 --> 01:21:35,643
and Jupiter will become
a rogue planet.
1416
01:21:37,710 --> 01:21:41,076
All that's left
of our once strong mafia family,
1417
01:21:41,143 --> 01:21:44,710
the Sun, eight planets,
and countless moons,
1418
01:21:44,777 --> 01:21:47,710
is the small, weak white dwarf.
1419
01:21:47,810 --> 01:21:51,710
Eventually, a white dwarf cools
so much that it no longer
1420
01:21:51,777 --> 01:21:56,209
emits radiation, and it becomes
what we call a black dwarf.
1421
01:21:58,410 --> 01:22:01,209
And this is basically
just a burnt-out shell
1422
01:22:01,309 --> 01:22:04,810
of a star composed of
oxygen and carbon.
1423
01:22:06,343 --> 01:22:08,209
It can form a carbon crystal,
1424
01:22:08,309 --> 01:22:10,252
which we happen
to call diamonds.
1425
01:22:10,276 --> 01:22:14,610
So think of a black dwarf as
a diamond in the sky.
1426
01:22:17,910 --> 01:22:22,543
A cosmic gem destined to
wander the galaxy for eternity.
1427
01:22:28,410 --> 01:22:31,853
Our solar system formed
from chaos but grew
1428
01:22:31,877 --> 01:22:36,143
from collaboration between
the planets and the Sun.
1429
01:22:36,209 --> 01:22:37,643
We know the planets affect us.
1430
01:22:37,710 --> 01:22:40,209
We know the Sun affects us...
In a few billion years,
1431
01:22:40,309 --> 01:22:42,109
the Sun is really gonna
affect us.
1432
01:22:42,176 --> 01:22:43,977
The more we look at this stuff,
1433
01:22:44,043 --> 01:22:46,543
the more we realize that
everything affects everything
1434
01:22:46,610 --> 01:22:48,343
else, including us.
1435
01:22:49,410 --> 01:22:52,443
Without all of
these things interplaying,
1436
01:22:52,510 --> 01:22:55,010
the Earth wouldn't have
the stable environment
1437
01:22:55,076 --> 01:22:56,910
that we have today,
and life wouldn't be
1438
01:22:57,010 --> 01:22:58,276
able to exist.
1439
01:22:58,309 --> 01:23:00,910
And so the chances are small,
but it's worked out well for us.
1440
01:23:03,643 --> 01:23:06,753
As we piece together
the events that have
1441
01:23:06,777 --> 01:23:08,643
we think shaped
our solar system,
1442
01:23:08,710 --> 01:23:11,309
we step back and think about
all the moving parts,
1443
01:23:11,410 --> 01:23:14,977
all of the chance encounters,
all of the chaos.
1444
01:23:15,043 --> 01:23:17,209
And it's hard not to think
that we're really
1445
01:23:17,309 --> 01:23:19,643
lucky to be sitting here
on this planet Earth.
1446
01:23:19,710 --> 01:23:21,977
In the future,
1447
01:23:22,043 --> 01:23:24,643
our mafia family will be gone.
1448
01:23:24,710 --> 01:23:27,710
But somewhere
out in the Milky Way,
1449
01:23:27,810 --> 01:23:33,109
a new mobster star system may
rise from the ashes of our own.
1450
01:23:34,109 --> 01:23:35,386
One of the trends that we see in
1451
01:23:35,410 --> 01:23:38,252
our universe is that
destruction leads to creation.
1452
01:23:38,276 --> 01:23:42,386
The fact that our star is
gonna one day die
1453
01:23:42,410 --> 01:23:44,810
doesn't mean that it's
the end of anything.
1454
01:23:44,910 --> 01:23:47,143
It's the beginning of
something new.
1455
01:23:47,209 --> 01:23:49,443
So I think in the future,
it's only going to get
1456
01:23:49,510 --> 01:23:50,810
more complicated,
1457
01:23:50,877 --> 01:23:53,486
more interesting, and we're
gonna find out just how dynamic
1458
01:23:53,510 --> 01:23:55,143
a place the universe really is.
1459
01:23:55,193 --> 01:23:59,743
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