Welcome back to the second part of our special, 2-part episode on finding and preventing asteroids
from hitting Earth.
In the first half, which you should totally watch first, we discussed the threat from
asteroids, and what observatories and surveys are actively searching for dangerous space
rocks.
But let’s say that we do find an asteroid, and we know with a high degree of certainty
that it’s going to smash into the Earth in the future.
What can we do about it?
What missions, techniques and technologies do we have at our disposal?
Before we get into these ideas, though, it’s important to map out the problem, so you can
understand why the solutions might not be as simple as you’re hoping.
First, anyone who’s played Kerbal Space Program understands that traveling in space
is all about orbits.
It’s not that a space rock is on a collision course with Earth, although there could be
some on highly eccentric orbits.
It’s that Earth shares a region with hundreds of thousands of rocks known as Near Earth
Asteroids.
Instead of a cosmic shooting gallery, imagine an asteroid race track, where various objects
are going around and around the Sun in a cloud with the Earth.
The Earth’s gravity, and their interactions with each other can cause their orbital trajectories
to change.
A previously safe asteroid could be jostled into a new orbit that could bring it into
a collision course with Earth after many many orbits into the future.
Chaos reigns with these calculations, and beyond a number of orbits, it’s hard to
predict the future trajectories again.
Which is why we need to be constantly vigilant to the skies.
The asteroids themselves aren’t the same either.
Some are that classic chunk of rock, that you’ve seen the Millennium Falcon dodge,
but many others are just a pile of rubble, held together by mutual gravity.
So, let’s imagine the various observatories and surveys we discussed in the previous episode
do turn up an asteroid with a high likelihood of crashing into Earth, what can we do about
it?
I know Bruce Willis movies have taught us all everything we need to know, but unfortunately,
Armageddon has misled you - on many levels.
Again, it’s not that an asteroid is on a collision course with Earth, it’s that the
orbits of Earth and a killer space rock could overlap in the future, at the same time.
That’s an impact.
And in order to avoid the impact, you need to change the orbit of the asteroid every
so slightly, so that its orbit crosses the Earth’s orbit at a time when the Earth isn’t
there.
Small changes make a big difference over time.
If you’ve only got a few months of warning, there isn’t much you can do, but if you
have years or even decades to push the asteroid, you can make the slightest change to its trajectory,
and things will work out well for us in the long run.
I’m going to start with the more mainstream ideas first, and then get into some of the
stranger ones.
The mostly commonly discussed idea is known as a kinetic impactor.
In other words, you smash something heavy and fast into the asteroid, and the impact
slightly changes its orbit.
We actually have a lot of experience with this, including the Deep Impact spacecraft
and NASA’s LCROSS mission.
But these were designed to crash into their targets and kick up some debris so that astronomers
could study them.
The goal wasn’t to completely change their orbits.
There’s a collaboration mission in the works between NASA and ESA called the Asteroid Impact
and Deflection Assessment, which could send a spacecraft to the asteroid 65803 Didymos
for a close encounter in 2022.
The mission will consist of two spacecraft: a NASA built impactor, and ESA’s orbiter.
If all goes well, the mission will launch in 2019, potentially visiting another asteroid
on its way to Didymos.
The impactor will smash into the asteroid, and then the orbiter will stick around and
calculate the change in trajectory from the event.
After this, we’ll have a better idea if impactors are the right way to go.
The other main route is known as a gravity tug.
Instead of slamming into the asteroid in a single event, a gravity tug pulls slowly and
steadily over a long period of time to gradually change an asteroid’s trajectory.
By positioning a massive spacecraft relatively close to the asteroid, they pull on each other
with mutual gravity.
The asteroid attracts the spacecraft and the spacecraft attracts the asteroid.
By constantly firing a nuclear powered ion thruster, the spacecraft would maintain a
constant distance from the asteroid.
And slowly but surely, the asteroid’s trajectory would change.
As part of its asteroid exploration plans, there was a mission in the works called the
Asteroid Redirection Mission, which would have tested out this technology with a solar
powered ion engine.
Unfortunately, the Asteroid Initiative was canceled earlier this year, so we’ll need
to wait longer to find out if this is an effective way to move asteroids around.
I just talked about the more traditional ideas.
In a moment, I’m going to talk about the more extreme ideas proposed to shift asteroid
trajectories, but first I’d like to thank:
Quan Nguyen (nwen) Richard Chapman
Robert Wenzel Pam Hyland
John Gallant Bjorne Gonneroe
And the rest of our 762 patrons for their generous support.
If you love what we’re doing and want to get in on the action, head over to patreon.com/universetoday.
Now we’re going to get into the stranger ideas for pushing an asteroid out of the way.
I’d like to give credit to Universe Today’s senior editor Nancy Atkinson for collating
these ideas in a story we did earlier this year.
I’ll put a link to her story in the description:
The classic science fiction idea for dealing with asteroids is to blow them up with nuclear
weapons.
Turns out this isn’t the best idea.
For the rock and metal asteroids you’re going to have almost no effect on their mass.
And for those rubble piles, you might even make things worse, by breaking one asteroid
into a collection of spacerocks with the same trajectory.
Now many places across the planet get an asteroid strike.
But we’ve got a lot of nuclear warheads, and we’ve got rockets capable of intercepting
asteroids, so if we learned about a killer asteroid, this is probably the strategy nations
of the world would go with.
There is another use for nukes, though.
Instead of impacting the asteroid directly, you explode your weapon relatively nearby,
vaporizing a chunk of the asteroid’s surface.
This causes a slight thrust from the asteroid itself.
This technique might even be more useful for comets, which are covered in volatile ice
and gasses.
You can take this ablation idea, but do it more slowly.
Using lasers, of course.
You could send a laser-equipped spacecraft to the asteroid.
It would use solar power to charge up its capacitors, and then release the energy in
a powerful laser blast that would vaporize some material on the surface of the asteroid.
This would act like a tiny thruster on the asteroid giving it a slight kick.
Instead of a laser, you could use a giant parabolic mirror in orbit around the asteroid
which would focus sunlight onto the surface of the rock, heating up material and acting
like a thruster.
The next idea is to just install thrusters on the asteroid.
Stop the asteroid’s rotation and then just fire your thrusters, ideally using fuel that
you harvested from the asteroid.
Break apart water into hydrogen and oxygen, which is a handy rocket fuel.
Another set of ideas focuses on the fact that the Sun is constantly pushing on everything
in the Solar System with its photons.
This force is essentially zero for the planets, but for the smaller objects, this photon force
as well as the radiation from the asteroid itself can make their rotation, tilt and orbit
unpredictable over long periods of time.
This is known as the YORP effect, and it could be enhanced with our technology.
There have been various ideas to wrap part of an asteroid in reflective mylar, or paint
part of an asteroid white or silver, and another part black to maximize the force.
Another really interesting idea is using mass drivers.
This would consist of an electromagnetic railgun installed on the surface of the asteroid.
Automated solar powered rovers would mine the surface of the asteroid and deliver material
to the mass driver.
It would then accelerate this material into an escape trajectory.
With each chunk of material thrown off, the asteroid itself receives a tiny kick in the
opposite direction, and this could be used to slowly move it.
One additional advantage to this technique is with the right timing, you can send this
mined material into more useful orbits for the future.
You make the asteroid safer, while also mining valuable resources.
It’s a great idea, in theory.
Finally, we talked about impactors earlier in the episode.
But you can do this technique in slow motion.
Instead of a single catastrophic impact, you could bump against the asteroid with a giant
airbag.
Over and over again.
This makes things simple because you don’t have to be concerned about the orientation
of the asteroid itself.
Just bump, bounce back, accelerate and bump again.
Conclusion: So which of these ideas is going to work best?
Right now, all we have are studies, and planetary astronomers still argue over which one is
the best.
We need to test them out.
We need to send missions to the asteroids, try out the different techniques and see which
one gives us the biggest bang for the buck.
Once humanity has finally gotten a handle on this threat, once we can identify dangerous
space rocks and move them into safer orbits, we’ll have taken one existential threat
completely off the table.
Of all the ideas for stopping an asteroid, which ones do you prefer?
Which technologies should we invest in developing further, and which are just science fiction?
Let me know your ideas in the comments.
In our next episode, we look at the mighty Space Launch System, and some of its possible
goals.
What could you use the most powerful rocket ever built for?
I’ll get into that, next time.
For our playlist, the asteroid hunting continues.
The first video is part 1 of this series, so if you missed that one, check it out first.
Then PBS Space Time takes a crack at stopping asteroids.
I haven’t actually watched this video, but I trust Matt to do a good job.
Bill Nye talks about the problem.
A lecture with Neil Degrasse Tyson about stopping asteroids, and then an even longer, more in-depth
lecture from NASA.