It's a scientific fact that the planet Earth
will be hit by cataclysmic asteroids in the future.
Assuming we can see them coming, what can we do to stop them?
[MUSIC PLAYING]
Space is swarming with lots of really fast moving rocks,
like the planet Earth, but also like that 19-meter-wide wide
chunk, that blazed across the sky above the Russian town
Chelyabinsk, in 2013, exploding in the air
and across Russian dash cams, with the power
of up to half a megaton of TNT.
(RUSSIAN ACCENT) In post-Soviet Russia, space explore you.
Now, Russia does seem to get hit a lot.
The Tunguska event of 1908 was even bigger,
when a 100-meter space rock exploded
to flatten 2,000 square kilometers of forest
in Siberia.
Now, there were no recorded fatalities in either case.
Tunguskia was very isolated.
And the Chelyabinsk asteroid came in at a shallow angle,
so it had lots of atmosphere to burn up in.
Had it been a direct hit, then a city of over one million people
would have been devastated.
Now that's pretty lucky.
But so far, we've all been lucky.
Impacts have tended to happen in remote regions.
But now that more and more of the world
is covered in urban areas, the chance of a catastrophic impact
is increasing rapidly.
It's really not a matter of if, just of when.
So when can we expect the next killer asteroid?
And can we stop it?
That depends on how bad the situation is.
Let's run through the levels of catastrophe.
OK.
A rock less than 10 meters in diameter
vaporizes harmlessly in the atmosphere.
This stuff isn't a problem.
At least 40,000 tons of it rains down on the Earth every year,
mostly in the form of pebbles and smaller.
These are the shooting stars that you see on a dark night.
Meteors 20-100 meters in size have the kinetic energy
equivalent of a thermonuclear explosion.
And this is a city killer on a direct hit.
We expect something like this once every century or so.
Now, we just had one.
But that does not mean we won't get one tomorrow.
For a rock around 500 meters in diameter,
the strike will have the energy equivalent
of all currently operational nuclear weapons in the world.
This devastates a country or makes a tsunami.
Expect one of these at least every 50,000 years or so.
Of course, it gets worse as you get bigger.
At two to three kilometers, the sky
goes dark from the ejector, and nuclear winter effects
global climates.
These happen every couple of million years.
Much larger than this and the planet
is showered in molten rock.
Nuclear winter lasts decades.
Oceans are acidified.
And most life on Earth dies.
An asteroid of this magnitude probably killed the dinosaurs
65 million years ago, hitting the Yucatan Peninsula
with the power of a billion megaton hydrogen bombs.
Earth gets smacked this hard every 100 million years or so.
Now the chance of any one of these killers on a given day
is tiny.
But small probabilities have a way
of adding up to a certainty, over time.
That means a big one will hit again.
And we can only stop it if we know it's coming.
There's been some good work.
Astronomers around the world have worked together
as part of the Spaceguard Program
to find and track most of the biggest, one kilometer plus,
comets or asteroids that cross Earth's orbit.
Those are called Near Earth Objects, or NEOs.
Good news-- none are coming close for centuries.
There are a couple of 500 meter bad boys that
have a very small chance of hitting in the late 2100s,
and the 300 meter Apophis, who will buzz us
inside the orbit of the geosynchronous satellites
in 2029 and 2036, but will almost certainly not hit.
So we've got some time.
But what about the NEOs the size of the Chelyabinsk or Tunguskia
rocks, Potential city killers.
We have no idea where most of these are.
These things are very faint specks
in the deep dark of space.
And current monitoring programs can only find a fraction.
This is probably something we want to deal with.
There are efforts.
The nonprofit B612 organization is
fund raising to launch the Sentinel infrared telescope,
that will orbit the sun and look outwards,
tracking hundreds of thousands of NEOs.
They need $450 million.
But that's less than the box office
take of the movie Armageddon.
So you know, we either pay to save the world,
or pay to watch Bruce Willis pretend to.
And speaking of Armageddon, what do
we do if we spot an incoming city killer,
or for that matter, a planet killer that we somehow missed?
Is there even anything we can do?
Absolutely.
But the approach is going to depend on how fast we can act.
Caught early, we have options.
See, the Earth is a very small target
on the scale of the solar system.
And Earth itself is moving pretty fast,
traveling its own diameter once every seven minutes.
Let's say we catch this killer rock at 10 years out.
We need to slow it down or speed it
up so that it is behind or in front of the Earth.
That means making it arrive just seven minutes later or seven
minutes earlier.
So divide seven minutes by 10 years.
We need to change its speed by roughly one part in a million,
and we save the world, and get to have a parade.
We can also nudge it by a similar amount to the side.
The further out we catch it, the less we need to nudge it.
There are a few different ways to do this.
Number one-- brute force.
Just slam a heavy spaceship into the NEO to knock it off course.
This is kinetic impact.
A one ton impact gives the necessary one part
to a million momentum change needed to divert city killers.
Now unfortunately, this doesn't work
for planet killers, which are at least a million
times more massive.
Number two, nuke it, but miss.
Yup, explode a nuke right next to the rock and vaporize part
of the surface.
The pressure of the nuke, and of the ejected asteroid bits,
will push the NEO off target.
A regular nuke would be fine for smaller asteroids.
But for a planet killer, you're going to need a few 50 megaton
Tsar bombs.
Thanks again, Cold War.
Number three, graffiti.
Seriously, arm a spacecraft with a cosmic-sized can
of spray paint, and color one side of the asteroid white.
The sun's light will push harder on the more reflective side,
slowly pushing it just far enough off course to miss us.
A similar proposal fixes a giant light sale
to the side of the rock.
Now for this option you're going to have to catch it early.
Number four, the weirdest deflection option--
a gravitational tractor.
Fly a 20 ton spacecraft alongside the object for 10
years, and their mutual gravity will pull the impactor
off course.
Options are great.
In fact, I don't want to attempt more than one,
because once the first one fails,
it may be too late to start again.
The real trick is getting politicians
to agree to something that involves scientific uncertainty
and long term thinking.
Hm, maybe we should do a Kickstarter to save the world.
OK, let's address the worst case scenario.
What if we catch this thing at the last minute,
or fail to act for other reasons?
The asteroid or comet is heading straight for us.
And we have a month or two, at most.
At this point, we can't deflect a large impactor.
We have to blow it up.
Now people often say that you shouldn't explode NEOs.
You'll just get lots of hard to track fragments.
But at this point, tracking isn't even that helpful.
And lots of small bits are much better than one big bit.
My favorite idea so far is the Hypervelocity Asteroid
Intercept Vehicle.
The idea is that you launch a thermonuclear device
at the rock, but you lead with a very high speed kinetic
impactor, that creates a nice, deep crater for the nuke
to explode in.
This uses the nuke's energy much more efficiently,
sending shockwaves through the asteroid, that will break it
into much smaller pieces.
That is, if you believe the supercomputer simulations
of HAIV team, a one megaton H-bomb
should break up a 500 meter asteroid nicely,
although it depends on the structure of the rock.
A loose, gravitationally-bound rubble pile
is obliterated, while a single rock will be fragmented.
For a giant asteroid, you're going to need a gigaton blast.
And such devices don't exist.
Should we build one just for this?
I don't know.
But without question, a better option
would be to build the infrastructure needed
to detect and deflect all dangerous objects much,
much earlier.
To me, this is amazing.
We are a species capable of defending
our world from a planet-killing meteor strike.
Or we could be, soon.
Science has given us such incredible power--
among other things, to serve as custodians of the planet Earth.
But what does it take?
Just a little support from enough of us.
Fund Sentinel.
Petition our leaders.
Study hard and do some mad astronomy or rocket science.
Check some links in the description.
And assuming no giant asteroids hit in the meantime,
I'll see you on the next episode of "Space Time."
In a recent episode we talked about the origin
of life and the Fermi paradox.
And you guys had some extremely interesting points.
William George, and a number of others,
note that any civilization advanced enough
to colonize the galaxy would also be advanced enough
to choose not to do so.
Now this may well eliminate a number
of potential galactic empires.
But all of them, with 100% efficiency?
Great filter items based on the presumed psychology
or sociology of advanced species aren't really compelling,
because only one such species needs
to make a different choice to not stay at home,
and we have galaxy-wide colonization.
It may be that advanced civilizations'
psychos sociological evolution converges
on an extremely narrow range of outlooks and motivations.
But even in that case, there are sure to be exceptions.
794651519, and a number of others,
point out that maybe our definition of life
is too restrictive.
Does life have to be chemical?
Does it have to be cellular?
Well actually, there's good reason
to think that extraterrestrial life might be chemical.
From everything we've seen in this universe, the arrangement
of atoms into molecules and molecular structures,
via chemical bonds, seems to be the process most
able to support extreme diversity
and complexity of form.
But even if life can arise in other ways,
that just increases the number of lifeforms
that we should be able to see.
And so it makes the Fermi paradox even more paradoxical.
Sam Shields asks whether Panspermia
is suggesting that life only arose
on one planet in the Milky Way before being spread everywhere.
Well first let me note that Panspermia is far
from being an accepted theory.
It's a cool one.
And it might be true, which is why we mentioned it.
And yes, that's the attraction of it.
Life would only have to arise once
in the galaxy, which allows the initial event of abiogenesis
to be very unlikely, and yet have life arise quickly
on another planet.
The big challenge is getting life-infested rocks
to spread through the galaxy.
Stars are very far apart.
There are ideas on how this might happen.
But it's not obvious that it's possible.
Now DivShadow, and a number of others,
told me that the Reapers wiped out all advanced civilizations.
Well, I choose the ending where Shepard saves the galaxy.