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00:00:02,243 --> 00:00:06,410
A small black star
floats through space.

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00:00:06,510 --> 00:00:10,843
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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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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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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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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The origin of
the solar system was chaotic

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and violent...
Planets colliding,

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planets even changing places.

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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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Just think about
how much our view

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of the solar system has changed.

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The planets used to be
so far away from each other,

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and of course, they had nothing
to do with each other.

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And now, the history is all
about the interaction.

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So the idea that everything
is just

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its own world and doesn't
interact is completely wrong.

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We like to think of astronomy
as looking up,

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looking outward,
away from ourselves.

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But the more we do that,
the more we realize how

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connected we are
to everything out there.

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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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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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In this tale,
that's the birth of the Sun.

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But exactly how that happens
is a mystery.

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When we're trying to figure out
how the solar system began,

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you know, we don't have
a time machine.

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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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Meteorites are pieces of
the solar system from

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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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our solar system even formed.

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By studying them,

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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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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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the history of the formation
of our solar system.

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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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00:04:33,309 --> 00:04:35,510
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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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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00:04:47,410 --> 00:04:49,710
made in stars
that no longer exist.

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00:04:51,510 --> 00:04:53,786
The Murchison meteorite
contains grains

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00:04:53,810 --> 00:04:56,910
from at least
46 different stars.

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00:04:58,410 --> 00:05:00,943
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

88
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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00:05:21,109 --> 00:05:23,343
could come from one of
a number of places.

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00:05:23,410 --> 00:05:25,743
The material from lots of stars'

95
00:05:25,810 --> 00:05:28,943
atmospheres
could be mixed in there.

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00:05:29,043 --> 00:05:31,643
In the mix were
the ingredients to build

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00:05:31,710 --> 00:05:33,443
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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00:05:35,510 --> 00:05:37,943
the gas and dust
to form the Sun.

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00:05:39,309 --> 00:05:42,043
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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00:05:45,910 --> 00:05:48,586
in the last couple of decades
about the Milky Way

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00:05:48,610 --> 00:05:50,486
is there's a giant stream
of stars that's

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00:05:50,510 --> 00:05:52,943
stretching across virtually
the whole sky.

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00:05:56,309 --> 00:05:58,910
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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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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00:06:34,610 --> 00:06:37,285
the Milky Way is tearing
Sagittarius apart,

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00:06:37,309 --> 00:06:39,010
ripping stars out of it.

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This is truly intergalactic
cosmological drama at play.

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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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00:07:44,010 --> 00:07:47,610
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

143
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

147
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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00:08:31,410 --> 00:08:34,610
the Sagittarius Dwarf passing
through our galaxy

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00:08:34,710 --> 00:08:36,343
over five million years ago.

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00:08:36,410 --> 00:08:39,443
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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00:08:45,610 --> 00:08:48,943
4.6 billion years ago,

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00:08:49,043 --> 00:08:50,510
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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00:09:00,143 --> 00:09:03,043
As the gas cloud collapses,

158
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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00:09:10,510 --> 00:09:16,410
The core is the protostar
that will later become our sun.

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00:09:16,510 --> 00:09:20,786
The protostar drags in
more and more gas and dust,

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00:09:20,810 --> 00:09:24,410
creating a region of materials
spinning around it

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00:09:24,510 --> 00:09:26,910
called the protoplanetary disk.

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00:09:27,010 --> 00:09:31,143
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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00:09:43,610 --> 00:09:47,343
immediately reveals
a ferocious nature,

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blasting out supercharged jets
of radiation.

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00:09:52,309 --> 00:09:57,486
The early sun was not
the calm, glowing orb

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00:09:57,510 --> 00:10:00,943
that we see in our sky today...
It was far more chaotic.

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00:10:03,209 --> 00:10:05,843
It's sort of like
in its toddler phase.

174
00:10:05,910 --> 00:10:07,943
It was acting up all the time.

175
00:10:10,109 --> 00:10:13,143
It has all of this energy that
pushes material off of

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00:10:13,209 --> 00:10:15,043
the surface and launches it into

177
00:10:15,109 --> 00:10:16,309
what we call the solar wind.

178
00:10:18,610 --> 00:10:21,243
The blizzard of
particles races out

179
00:10:21,309 --> 00:10:23,910
at over a million miles an hour.

180
00:10:24,010 --> 00:10:27,043
It smashes into
the protoplanetary disk

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and blows the gas away.

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00:10:31,109 --> 00:10:35,143
At the same time, the Sun's
core heats up to 18 million

183
00:10:35,209 --> 00:10:37,085
degrees Fahrenheit,

184
00:10:37,109 --> 00:10:41,386
triggering the fusion of
hydrogen into helium.

185
00:10:41,410 --> 00:10:43,710
And that releases
a tremendous amount of

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00:10:43,810 --> 00:10:46,443
energy that eventually works
its way back to the surface of

187
00:10:46,510 --> 00:10:48,410
the star and comes out as light.

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00:10:50,143 --> 00:10:53,886
Finally, the Sun
becomes the recognizable

189
00:10:53,910 --> 00:10:56,109
sun that we see
in our sky today.

190
00:10:58,143 --> 00:11:00,886
The sun is now the Godfather,

191
00:11:00,910 --> 00:11:03,143
pulling the strings on
the solar system.

192
00:11:04,610 --> 00:11:06,810
The young Don's rise to the top

193
00:11:06,910 --> 00:11:09,986
triggers a power struggle
with its willful children,

194
00:11:10,010 --> 00:11:11,810
the planets.

195
00:11:11,910 --> 00:11:14,143
It's a brutal fight
for survival.

196
00:11:26,543 --> 00:11:29,243
4.6 billion years ago,

197
00:11:30,410 --> 00:11:34,743
our mob family rises in
a quiet suburb of the Milky Way.

198
00:11:35,810 --> 00:11:39,810
Its Godfather, the Sun,
forms from a collapsed

199
00:11:39,910 --> 00:11:41,143
stellar nebula.

200
00:11:44,910 --> 00:11:48,285
The greedy star scarfs down
most of the cloud of gas

201
00:11:48,309 --> 00:11:50,243
and dust, but just enough

202
00:11:50,309 --> 00:11:53,209
is left over
to build the planets.

203
00:11:53,309 --> 00:11:56,610
We're standing here on a big
planet, and we look up in

204
00:11:56,710 --> 00:11:58,986
the sky, and we see other
planets going around the Sun,

205
00:11:59,010 --> 00:12:02,285
and it's an obvious
and challenging question to ask,

206
00:12:02,309 --> 00:12:03,810
where did these planets
come from?

207
00:12:05,743 --> 00:12:09,410
How did the leftover gas
and dust build the planets?

208
00:12:10,943 --> 00:12:13,786
To solve the mystery,

209
00:12:13,810 --> 00:12:16,143
scientists study
other star systems

210
00:12:16,209 --> 00:12:18,343
across the Milky Way.

211
00:12:18,410 --> 00:12:19,886
We can't go back in time

212
00:12:19,910 --> 00:12:22,085
and watch our own
solar system forming.

213
00:12:22,109 --> 00:12:25,610
But we can look at other,
new solar systems as they're

214
00:12:25,710 --> 00:12:28,843
forming and use that to
understand how our own

215
00:12:28,910 --> 00:12:30,143
might have formed.

216
00:12:34,043 --> 00:12:40,943
Star system PDS 70
is one such system.

217
00:12:41,043 --> 00:12:44,943
It's young,
just 5.4 million years old.

218
00:12:47,309 --> 00:12:50,643
And nestled inside
the protoplanetary disk are

219
00:12:50,710 --> 00:12:54,843
two infant planets
feeding on gas and dust.

220
00:12:58,043 --> 00:13:00,986
We can see these baby
exoplanets pulling in

221
00:13:01,010 --> 00:13:03,610
material and creating
these gaps in the disk.

222
00:13:03,710 --> 00:13:05,910
It's an amazing discovery...
It's kind of mind-blowing

223
00:13:06,010 --> 00:13:09,710
that we can see a new
solar system being born.

224
00:13:11,643 --> 00:13:14,309
These snapshots,
these systems like PDS 70,

225
00:13:14,410 --> 00:13:17,986
are so valuable, because they
let us test our theories.

226
00:13:18,010 --> 00:13:21,043
We thought planets formed from
these discs of dust and gas,

227
00:13:21,143 --> 00:13:23,543
but we hadn't seen it until now.

228
00:13:23,610 --> 00:13:25,810
What we couldn't see was how gas

229
00:13:25,910 --> 00:13:29,243
and dust bind together
to grow into planets.

230
00:13:35,610 --> 00:13:37,185
That took an astronaut on

231
00:13:37,209 --> 00:13:40,410
the space station messing
around with breakfast.

232
00:13:42,810 --> 00:13:44,243
Ah.

233
00:13:44,309 --> 00:13:45,586
Don Pettit, this one astronaut,

234
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.

237
00:13:52,043 --> 00:13:53,643
And to his astonishment,

238
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."

250
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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