- We are planning to test out how you would defend Earth
from an incoming asteroid.
For the first time, helping humanity save itself
from a threat of a killer asteroid.
- An impact on Earth doesn't happen very often.
That doesn't mean they don't happen.
- This isn't the sort of thing
that we want to address at the last minute.
(pensive music)
- [Narrator] An asteroid impact
is a blockbuster kind of disaster.
- The comets are still headed for Earth.
(dramatic music) (blast rumbling)
- [Narrator] But is the threat of global destruction
something we should actually fear?
66 million years ago,
an asteroid the size of a mountain
wiped out the dinosaurs
and altered the global climate for years.
So could we suffer the same fate?
- We don't want to be dinosaurs,
but we're not as worried about it
because we have been cataloging
all the different sizes of asteroids and tracking them.
At this point we feel like we know
100% of all of the dinosaur killers
and they're not coming towards Earth.
- [Narrator] Space agencies including NASA
are confident they're tracking asteroids
big enough to cause a major extinction event
and none of them are headed our way
in the foreseeable future.
But this doesn't mean we're safe.
- Scientists are mostly worried about asteroids
that are in the 100-meter kind of range.
- They are difficult to see because they're small,
because they are dark, and because they are really far away.
- [Narrator] But even though they're hard to spot,
these smaller asteroids can still do a lot of damage.
Take the Chelyabinsk meteor, which lit up headlines in 2013.
- A meteorite, or perhaps more than one,
passed over Southern Russia, eventually exploding in midair.
- It had detonated in the atmosphere
and that detonation was about two to three times
as much as a nuclear bomb.
- The shockwave can actually break windows.
And the windows, they are going to harm people.
- [Narrator] And that asteroid was only about 65 feet wide.
Even relatively small asteroids
could cause catastrophic damage.
So what are scientists doing
to prevent the next major asteroid disaster?
- We have a fantastic team of planetary defenders
trying to find the near-Earth asteroids
that perhaps pose an impact threat.
- There are campaigns,
not only in the U.S., but all around the world,
trying to observe them and trying to classify them
and trying to understand their orbits.
- Of this 140-meter-and-larger size range,
it's estimated there's 25,000 of those.
To date, we're probably just a little
over a third of the way in finding all of those asteroids.
NASA has been doing this a long time.
And it became more formalized in 2016
into the Planetary Defense Coordination Office.
- [Narrator] Yes, planetary defense.
By 2022, it plans to launch
its very first spacecraft mission called DART,
short for Double Asteroid Redirection Test.
- We want to know whether or not we will be able
to redirect an asteroid.
- [Narrator] Redirect.
That means changing the path of an asteroid.
To test if this technique could work,
it needs to find not one, but two asteroids.
- [Elena] One is Didymos, the main asteroid,
and then it has a small moon that orbits around it
called Dimorphos.
So DART's goal is to hit Dimorphos.
- [Narrator] , that's right, it's trying to move a moon.
- To see whether or not we can change its orbit.
- Even though the Didymos system
is considered a potentially hazardous object,
which means it comes actually pretty close to Earth,
there's no way, by us hitting the moon of the object,
that it changes the trajectory of the larger asteroid.
We are testing out a technique called a kinetic impactor.
About four hours out before the impact,
the spacecraft becomes fully autonomous.
It will point itself towards the moon,
make all the maneuvers necessary
to slam itself into this really small object.
So really, from 60,000 miles away,
you basically started off
and you guided yourself into a 160-meter object.
It is very impressive.
And hard.
- [Narrator] To determine whether the nudge was successful,
scientists will look for changes in the moon's orbit.
If the mission is a success,
that means this might be an effective method
to deflect an asteroid
discovered to be on a collision course.
- [Paul] If we catch this asteroid
early enough in its trajectory,
we should be able to deviate it enough
so that it just misses the Earth.
- [Narrator] But what if there isn't enough time
to deflect an asteroid?
- [Paul] The answer is not purely scientific.
It also has to do with the politics
of how to deal with this.
Even though it is called planetary defense,
there are few countries that can really do something
and those countries are those
that have space mission capabilities.
- [Narrator] And the countries who don't
have such capabilities will have to depend
on the goodwill of those who do.
- Will those countries be able and willing to do something?
- [Narrator] Right now experts are conducting
regional risk assessments
and drawing up notification and evacuation plans.
- At the Planetary Defense Conference,
which is a gathering of researchers
who work in planetary defense from around the world,
we'll have these exercises
where it's a hypothetical scenario
where an asteroid is discovered
that has some probability of impacting Earth,
what their roles might be in addressing an impact threat.
And ideally you would find that object,
perhaps a couple of orbits
before it ever poses an impact threat,
so that you would have years or decades
of notice to plan for it.
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