Original subtitles

A large object suddenly about to strike our planet.

The fear and panic that this can inspire

is the stuff of science fiction movies.

But scientists say that this sort of impact event

could actually happen.

December, 2006.

NASA submitted a detailed 270-page report

to the U.S. Congress.

This study assessed the risk of an impact

by what are called near-Earth objects.

It found that the number of small space objects

posing a threat, such as comets and asteroids,

came to about 20,000.

These objects have the potential to

take out civilization as we know it.

So we really owe it ourselves to monitor the skies,

and find and track all of the fairly large ones

that could cause civilization-ending events.

It's not a matter of if they will hit.

It's a matter of when.

Astronomers around the world have

joined forces to identify potentially hazardous objects

in space with the goal of protecting Earth from this danger.

In the course of their surveys

they have discovered new threats.

For example, an asteroid that might collide with Earth

in the year 2029.

There would be extensive damage at the very

location of the impact, sort of ground zero.

When will an object next impact our Earth?

How are scientists addressing this threat

from outer space?

The Sonoma Valley in California.

This valley has long boasted prime agricultural land,

including world famous vineyards.

But there's someone here who's thoughts have turned

from terroir to terror,

the threat of a potential asteroid collision.

Russell Schweickart, nicknamed Rusty.

Nice to see you.

He's a former astronaut who flew on

Apollo Nine, and has circled the globe 151 times.

Would you come in?

Schweickart's space flight took place in 1969.

The mission was designed to check out systems in advance

of the moon landing scheduled for later that year.

The primary objective was to test fly the Lunar Module,

piloted by Schweickart, in the zero gravity of space.

And Schweickart undertook the first ever space walk

without an umbilical cable.

Separated from his comrades, he faced all alone

the blackness of space.

He was brought face-to-face with planet Earth's

exposure to catastrophe.

The three of us were looking down at the Earth,

which is spectacular at night because of lightning

and weather fronts and things, cities lit up.

It's really beautiful, but everyone once in a while

you would see a little flash.

Earth is constantly exposed to collisions

with objects from space.

But Schweickart was the first to experience

this vulnerability on such a personal level.

Shooting stars are meteors, space objects as small

as pebbles, or even grains of sand, whose entry into

Earth's atmosphere is a frequently observed phenomenon.

In 1992, a fireball appeared suddenly over Pennsylvania

in the United States, traveling toward the northeast

before breaking up.

Its descent was captured on camera thanks to the filming

of a local football game.

Over Spain in 2004, a shooting star blazed so brightly

it could be seen in the middle of the day.

However, shooting stars are created by objects so small

that they almost always burn up before they can

cause injury or damage.

Tunguska, Siberia.

Here on June 30th, 1908 occurred a catastrophic event.

A gigantic explosion.

Scientists from the Soviet Academy of Sciences

who reached the remote location were astounded at

the spectacle that confronted them,

millions of felled trees.

The area of leveled forest measured some

2,000 square kilometers, the size of Tokyo.

The fallen trees radiated away from one spot.

It was hypothesized that this was the epicenter

of an asteroid impact.

But there was a mystery.

Not a single fragment of meteorite, that is to say,

no asteroid remnant was to be found on the ground.

Was the Tunguska event the work of an asteroid, or not?

Recently, as research into this question continues,

a new fact has come to the fore.

Physicist Giuseppe Longo has been investigating Tunguska

onsite for two decades.

His colleague in this research is Luca Gasperini.

Their first expedition was in 1991.

They began searching the Tunguska area for

meteorite fragments that would prove that

the 1908 explosion was an impact event.

First they had to contend with the huge number of mosquitos

that breed in the Tunguska wetlands.

They split up into small teams and searched

the center of the blast area.

They took core samples from trees in the hope that

such a large explosion would have left traces.

Looking for meteorite fragments as well,

they also collected soil samples.

All their samples were transported back to Bologna

and stored in a warehouse.

During their first two research trips, 1991 and '99,

they collected soil samples from a total of 300 locations.

They're going to show us a soil sample taken in 1999.

Radio isotope analysis identifies the stratum

corresponding to the blast year, 1908.

X-ray examination of that stratum reveals something else.

OK.

Ordinarily in this region humus and

other debris form horizontal layers, but the tremendous

momentary force of the explosion compressed this area.

It also slanted the disposition of the layers.

However, no actual meteorite fragments were found.

If they were, that would prove the theory of

an asteroid impact.

They really wanted that physical proof,

so the two colleagues prepared for a third

research expedition.

This time they focused their attention on a small lake

eight kilometers north from the presumed epicenter.

The two colleagues were now hypothesizing that an asteroid

streaking in from the southeast exploded in mid air.

A portion then traveled another eight kilometers before

striking Earth and excavating the lake bed.

In 2008 the team made their third research trip.

They measured the depth of Lake Cheko

and took samples of the lake floor.

The results were as you see here.

The lake floor in cross section reveals a deep

angular depression.

It's markedly different from the lake bed structures

of other lakes nearby.

Furthermore, acoustic measurement of the lake floor

showed striations consistent with sudden external pressure.

A whole series of new discoveries

has by now fairly well established that the Tunguska event

was due to collision with a space object.

Yet not the smallest fragment of the impacting object

has ever been recovered, crucial evidence missing.

We've come to Sandia National Laboratories

In New Mexico, U.S.A.

As a nuclear weapons research facility,

entry is strictly regulated.

Mark Boslough is a physicist here,

studying large blast phenomena.

To address this question of the absence of object fragments

at Tunguska, he's using a supercomputer.

We knew from the old Russian expeditions

and photographs and mapping, we knew the area

over which trees had been blown down,

and we knew the pattern.

So we could match that with the size of the asteroid

that would blow those down.

After several months of computing,

Boslough concluded that the Tunguska explosion was caused

by the intrusion of a 50-meter diameter asteroid.

This is Boslough's simulation of the Tunguska event

created on the supercomputer.

The asteroid, 50 meters across, as wide as

an 18-story building is tall, blazed into Earth's atmosphere

as a meteor at 15 kilometers per second.

At an altitude of 8500 meters, it exploded.

At that moment its core temperature hit

24,700 degrees celsius.

It vaporized in an instant.

The energy released by the explosion propagated a shock wave

toward the Earth's surface, flattening forests and causing

widespread destruction.

To summarize, when the asteroid exploded, it vaporized.

That's the reason no fragments descended to Earth.

In this case, because it's coming in at an angle,

when it explodes the momentum carries that energy downward,

still very powerful.

But because that energy was directed downward,

the effects on the ground at ground zero, at Tunguska,

the effects we observe could have been caused by

a smaller asteroid.

Even a 50 meter wide asteroid

would have the impact of a hydrogen bomb.

What causes asteroids to approach Earth?

Between Mars and Jupiter lies a region called the main belt,

that is, the main asteroid belt.

The so-called minor planets, asteroids and other such

objects that populate it, number in the hundreds

of thousands, perhaps even the millions.

But since most lie outside the orbit of Mars,

they rarely approach Earth.

Sometimes, however, affected by the gravitational pull

of Jupiter or Mars, these objects are flung toward

the inner solar system.

If an asteroid approaches our planet,

there may well be a collision.

These are potentially hazardous objects.

And indeed, many asteroids have left their imprint

on the Earth's surface.

Gosses Bluff Crater in central Australia.

It has a diameter of 22 kilometers.

It is thought that this crater was created 140 million

years ago by the impact of an object from outer space.

The Barringer Crater, or Meteor Crater in Arizona

measures one point two kilometers across,

and dates back 50,000 years.

In the long history of the world there have been

quite a few such impacts.

By 2011 the number of confirmed craters reached 176.

The impact that caused the greatest devastation

was at the site shown here.

Mexico's Yucatan Peninsula.

A gigantic crater was gouged into the terrain here,

170 kilometers in diameter.

The impact took place 65 million years ago

during the cretaceous period,

when the dinosaur population was at its zenith.

What caused the impact was an asteroid as large as

10 kilometers across.

The dinosaurs were assailed by a gigantic blast

and subsequent inferno.

Dirt and ash then filled the atmosphere, blocking out

the sun's rays, yielding an extended period

of cold temperatures.

That led to the dinosaurs extinction.

It's estimated that an object large enough to cause

a global extinction of life, that is one that's

10 kilometers wide or more,

strikes Earth once every 100 million years.

Even something one-tenth that size would cause damage

tantamount to a nuclear holocaust.

Civilization as we know it would be imperiled.

Objects that size strike once every few hundred

thousand years.

Even an object in the 100 meter class would have

a catastrophic impact.

It could take out a large city.

Scientists estimate the frequency of strikes by these

smaller objects to be on the order of once

every few centuries.

Any substantial asteroid impact would cause destruction

on a scale that humanity has never experienced.

Three, two, one.

Christmas time, 2004.

In this happy season, shocking news made its way

around the globe.

Now the threat posed by an asteroid collision

was a reality reported by the media.

Let's pay a visit to the person who discovered this danger.

David Tholen, an astronomer at the University of Hawaii.

Hi, nice to meet you.

How are you today?

Doing well.

Tholen has already discovered

over a thousand asteroids.

This screen is telling us the status of the telescope.

Then on June 19th, 2004,

he spotted an object of particular interest.

The slit is closed, the wind screens are parked.

Here are photographs of it.

These are interval shots of the same sector of space.

When they are superimposed, you can see that

something has moved.

A nearby asteroid.

Two days after this sighting, however,

Tholen lost track of it.

He looked for it for months.

Then on December 18th he spotted it again.

Based on its previous and current positions,

he was able to calculate its orbit.

That is when he concluded that there was a

one in 300 probability that it would impact Earth in 2029.

Well, we were very excited because this was the

sort of thing that people looking for asteroids that could

potentially collide with the Earth...

Here we were talking about something that was just

25 years away.

The asteroid was estimated to be

400 meters in diameter, and to weigh 72 million tons.

Tholen chose a name for it.

Apophis.

That is the Greek name of the ancient Egyptian

god of destruction, a deification of darkness and chaos.

Astronomers all over the world began their own

observations of Apophis.

All of this news was breaking right around the time

of the Christmas season.

And so many astronomers, rather than spending the time,

the holidays with their families,

they were instead spending time with a telescope

measuring the position of this asteroid.

One of my colleagues called it the Grinch

that stole Christmas.

The telescopes of the world were trained

upon Apophis, and its orbit was carefully calculated.

In just three days the probability of a collision

was upgraded to one in 37.

The asteroid could actually collide with Earth

and wreak tremendous havoc.

It was starting to sound all too real.

If Apophis were to hit Manhattan Island,

you could probably say goodbye to Manhattan Island.

That's about similar dimensions.

If it reached Earth, Apophis would create

a four kilometer wide crater on impact.

Shock waves would further devastate thousands of

square kilometers all around.

Not just Manhattan, but all of New York City

would be destroyed.

Destruction would not be limited to the immediate vicinity

of the impact site.

One scientist has raised concerns that

it would be widespread.

Professor Seiji Sugita of the University of Toyko

studies the impact of space objects.

His team will simulate impact scenarios for Apophis

inside this special chamber.

They'll fire an eight-millimeter projectile into a basin

of sand at an effective speed of 1200 kilometers per hour.

The first simulation models the impact

on a planet without an atmosphere.

The ejecta curtain, the sheet of displaced material,

makes a perfect inverted cone.

Next the effect on a planet with an atmosphere,

like Earth, is simulated.

The ejecta curtain here forms, not a smooth inverted cone,

but a swirling vortex.

A closer look reveals a great difference

in elapsed time also.

In the no atmosphere simulation on the left

the sand subsided in point zero three seconds.

But in the atmospheric case simulated on the right

the sand stays aloft much longer.

Sugita estimates that the displaced dirt and dust would

stay aloft 100 thousand times longer on an actual

Earth-sized planet with atmosphere than one without.

Based on such simulations,

Sugita predicts that if Apophis collides with Earth,

it will project as much as three billion tons of dirt

and dust up into the stratosphere.

Some of it will remain in the atmosphere,

where for the next three months it will stay suspended,

blocking sunlight and cooling the entire planet.

There have been actual cases where enough particulates

have swirled up into the stratosphere to lower temperatures.

The eruption of Mount Pinatubo in 1991, for example,

spewed 300 million tons of dust and ash

into the stratosphere.

As a result, the amount of sunlight reaching

the Earth's surface was reduced by five percent.

And in the northern hemisphere the average temperature

dropped by point six degrees celsius.

If Apophis collides with Earth, it will send up into

the stratosphere ten times as much particulate matter

as the Mount Pinatubo eruption.

The damage would be incalculable.

The world's clearing house for information about

asteroid and comet discoveries is the Minor Planet Center.

Gareth Williams is in charge of compiling data on

more than 200,000 space objects.

When astronomers around the world observed Apophis,

they sent their information here.

It was Williams whose task it was to collect and correlate

all this data, and to publicize it to the global

research community.

As soon as Apophis was discovered, the Minor Planet Center

sent out requests to astronomers worldwide

for follow up observations.

Ascertaining whether Apophis would strike Earth or not

required extremely accurate data about its trajectory.

We need to find them, and we need to follow them

long enough that we can predict where they're gonna be

with accuracy years in the future.

And in order to do that you need long arcs of observation.

Responding to the requests by the Minor

Planet Center, observatories around the world trained

their telescopes on Apophis.

The astronomers then pooled their observational data,

and the asteroid's orbit was more accurately plotted.

The result?

In 2029, Apothos will approach Earth, but finally whiz by it

at an altitude of 32,500 kilometers.

That's closer than the orbit of a geosynchronous satellite.

Earth will have escaped an asteroid impact by

the slimmest of margins.

But Apophis is not the only near-Earth object

heading our way.

Calculating asteroid orbits is Makoto Yoshikawa's specialty.

He is sounding the alarm.

These objects pose an all too imminent threat.

Yoshikawa has calculated the trajectories of space objects

whose orbits take them close to Earth.

Here is what he's found.

The yellow circle is the orbit of the Earth.

Around it are clustered 5,700 asteroids.

Let's put them all in motion based on actual observation

and assessment of their orbits.

The red flashes show where the orbits of asteroids

intersect Earth's orbit.

Yoshikawa calculates that among the asteroids

approaching Earth, 205 have the potential to

collide with our planet.

Since others have yet to be discovered,

an Earth impact could occur at any time.

To discover any unknown objects that could collide

with Earth, an international organization

has been established in Italy.

It's called the Spaceguard Foundation.

It has been joined by observatories in seven countries,

including Japan, the United States, the United Kingdom

and Australia.

Participating in Japan is the Bisei Spaceguard Center.

Here the Japanese observatory is using two telescopes

to track and photograph space objects approaching the Earth.

Members of a six-person team take turns

monitoring the equipment.

They're looking for any movement that stands out

from the background array of stars.

In one evening they'll take 300 or 400 photographs,

and so far they've discovered over 1,000 asteroids.

When Rusty Schweickart observed Earth from space on

Apollo Nine, he felt keenly the danger posed by asteroids.

Motivated by his heightened sense of the threat posed

by such space objects, Schweickart is taking action.

His message.

An asteroid collision is inevitable.

However, humankind working together can defend against it.

So the question is, do we care

about future generations?

How much do we care?

Should we take action today to protect our grandchildren?

This is survival of the species.

The American government is now also

getting involved in plans to avoid an asteroid collision.

The summit of Haleakala on the Hawaiian island of Maui

has an elevation of 3,000 meters above sea level.

In 2008, the American government built a

new observatory here.

It's called Pan-STARRS.

The Director of Pan-STARRS Telescope One is Ken Chambers.

The Pan-STARRS One telescope was purpose built

to spot space objects.

Its field of view emcompasses 36 full moons at one time,

a large sector the sky.

It takes just one week to complete a full survey of space

as visible from this location.

Pan-STARRS is a small telescope, but in some ways

it's the biggest telescope in the world,

and that's because of its camera.

The camera is the largest camera in the world.

It's actually a CCD camera, about 40 centimeters across.

Thanks to this CCD camera exclusively

developed for Pan-STARRS, the telescope can spot

space objects 100 times fainter than could the telescope

used to discover Apophis.

We know many of the largest ones, but as you get to

the smaller and smaller ones that are still dangerous enough

to be a threat to life on Earth,

we still haven't found them all.

The plan for the Pan-STARRS observatory

is to identify several hundred thousand space objects

in three and a half years.

If an asteroid or a comet were to be found that was really

going to collide with Earth, how could we respond?

The United States has begun to formulate a strategy.

Three, two, one.

We have ignition and lift off of a Delta Two rocket

carrying Deep Impact.

In 2005, NASA conducted a grand experiment

in outer space.

The Deep Impact Mission.

The goal, to intercept a comet moving at

10 kilometers per second,

and strike it with a projectile called an impactor.

The ambitious plan called for the impactor to be launched

at the target from a distance of 880,000 kilometers.

That was one tough shot to make.

Moreover, the targeted comet was 133 million

kilometers from Earth.

Radio transmissions took seven minutes to travel each way.

Remote control from Earth was impossible.

To overcome these constraints, the impactor was outfitted

with a camera.

It could thus guide itself to the target.

Starting two hours prior to impact, the impactor received

no instructions from Earth.

It was a self-guided missile.

This is an image taken by the impactor itself

on its way to the comet.

It has fixed its sights on this bright spot in deep space.

Then it adjusts its own trajectory.

It makes three mid-course corrections in all,

and finally hits right on target.

This was proof that an extremely remote space object

traveling extremely fast could indeed be impacted.

The Deep Impact Mission did demonstrate rather effectively

that we have the technology to run into a near-Earth object,

should we choose to do so.

If you have enough time, 10, 20, 30 years prior to

a predicted impact, you can run into it and slow it down

just a bit so in 10 or 20 years it will miss.

In 2006, Yeomans and his colleagues were

largely responsible for producing a report for NASA

on the subject of space object impacts.

The report specified concrete measures that could be taken

to alter such objects' orbits.

This 15-ton spacecraft would land a solar-powered

plasma engine onto a threatening asteroid.

Over time it would literally push the asteroid

off its collision course.

Yeomans and the other NASA scientists alike felt that

given sufficient time, this could prevent an asteroid

from colliding with Earth.

The American government has committed $100 million dollars

to the Pan-STARRS project, and in fact,

plans to expand its observational capabilities.

So here's Pan-STARRS One where we just were.

We're building Pan-STARRS Two, the second one,

in this dome here.

Pan-STARRS One has been in operation since 2008.

Pan-STARRS Two is scheduled to come online by 2014,

and there are plans for a third and fourth

telescope as well, all to look for objects that might

collide with our planet.

Then if you find one, and there is one headed for Earth,

you want to find it...

If you find it a hundred years ahead of time,

and it's not gonna hit the Earth for a hundred years,

then we have time to do something about it, yes.

If it's headed for Earth, and it's gonna hit in 10 years,

we still have time to do something about it

if we all work together.

With the number of telescopes

increasing to four, the survey of near-Earth objects

can be greatly speeded up,

hopefully giving sufficient time to ward off disaster.

The Earth exists in space.

The threat of a collision with another space object

is ever present.

Even one such impact has the potential to

wipe out civilization.

But now humankind has awakened to this threat.

We are devising early warning systems and ways to mitigate

or avoid a major impact.

Observatories around the world are on the alert,

peering into the heavens every night,

keeping watch on those starry skies.