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Hank gives us the skinny on three plans NASA scientists have come up with to save Earth from an asteroid impact. Hopefully we'll never have to use any of them.

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 Introduction (00:04)

Hank: A while back I told you about some rogue asteroids whose threat to earth, while mathematically minuscule, is none-the-less real.

This raises the question of what our plan is for stopping one of these dastardly asteroids if we need to. 

Turns out we have three.

In 2007, NASA presented the United States Congress with 3 ways to save the world from an asteroid on a collision course with earth. 

Each plan has it's upsides and it's downsides, but together they cover pretty much every doomsday scenario Hollywood could dream up. 

 1. (00:31)

The first plan proposes using a "slow push". A strategy that involves sending a spacecraft to a threatening asteroid and then messing with it to alter it's orbit. 

For example, one of these methods called "ablation" would use a huge mirror to focus sunlight on a small spot of the asteroid. The heat generated from the beam would vaporize material on the surface creating a jet of gas and debris with just enough force to divert the asteroid's path. 

Another plan calls for sending a spacecraft that's so massive that it would serve as a "gravity tractor". By flying a super massive vehicle alongside an asteroid, gravity could pull the space rock out of the way. 

But, the slow push scenario that experts like the most is called the "space tug". In this version, a craft attaches itself to the asteroid and fires it's propulsion systems to nudge the rock onto a different course. 

All very elegantly simple, no? Actually, no. The problem with slow push plans is that they all involve inventing tricked out new spacecraft, and having them rendezvous with a rock millions of miles away. 

That's a lot of logistics, combine that with the fact that these techniques would only work on rocks less than 3 hundred meters across and it's time to look for plan B. 

 2. (01:35)

So what about brute force? I mean, you're trying to destroy a rock here, so lets not over think it. 

That's where the second plan comes in, kinetic impact. NASA's actually described this as the "most mature approach" but the whole idea of it turns me into an instant 7 year old. 

You just get a delta 4 rocket, you saddle it up with some high density impactors, like a huge chunk of depleted uranium and then you aim it away from your face and toward an asteroid. And kablam-o! It would be awesome!

But again, there are problems. Kinetic impacts are only effective on smaller, solid objects. And some of the bad guys out there roaming around are basically just several square kilometers of rubble held together by gravity.

An impact could potentially just turn them into many, many little asteroids instead of one big one. 

 3. (02:19)

So that leaves us with only one other option and you may know what I'm talking about here. The nuclear option. 

NASA physicists say it would just take a small megaton neutron bomb to divert the path of even a large asteroid. And computer models, they found that the nuclear option was 100 times more effective at deflecting asteroids of all sizes than any of the non-nuclear options. 

So there's our solution. But obviously there are some drawbacks here. First of all, experts point out that you can't just launch some leftover warhead. You need a specialized nuclear device on a heavy lift launch vehicle and the ability to time the explosion precisely. Even though the explosion would be most effective if it took place on the asteroid's surface, or even inside of it, the official recommendation is to do a standoff explosion. Detonating the bomb during a fly by. This cuts the risk of blasting the asteroid into a bunch of radioactive fragments hurtling towards earth which would not be ideal.

But finally, there's this little snag. The International Comprehensive Test Ban Treaty prohibits nuclear explosions in space even for scientific research. So a plan like this would require international co-operation and approval. Now hopefully the prospect of all of our live turning into some bad 90's disaster movie would be enough to get the nations of earth to work together on this. But lets just say, I hope we never need to find out. 

 Ending (03:31)

Thanks for watching this episode of SciShow. Again, I hope that we never need to use any of this information, but it's good that we have it anyway. 

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We'll see you next time.