Asteroid ace keeps NASA grounded

In terms of the technical options, hitting an asteroid with something is one alternative. And the other alternative would be to put something that has a thruster on the asteroid, and nudge it into a different course over a long time frame. Does that pretty much cover it?

Oh, no. Those are just two of many options. You could put up a sun-focusing mirror nearby, and focus sunlight on one side of the asteroid, and the ablation of material on the front side would introduce some thrust on the asteroid. You could mount a shuttle engine on one of these things, but then you’d have to worry about the rotation. You’d have to pulse every time it came back to the same location. Or you could have mass drivers. That has been suggested.

The weapons lab folks suggested buried nuclear devices for standoff nuclear blasts that would ablate the front side and introduce a thrust. Or blow it up soon enough so that the shrapnel would miss the earth. You don’t want to blow this thing up just before impact, because then you’ve got a shotgun effect that would be worse. Not too many people are comfortable with this nuclear option, but the Lawrence Livermore folks were sort of keen on that one, as was [nuclear-energy pioneer] Edward Teller in his day. …

There are a lot of techniques that could be used, assuming you have the time. The key is, you have to find them early, and then things are tractable. If you find it too late, within a year of impact, there’s not a whole lot you can do. You just evacuate, if it’s small enough to cause only local damage. And if it’s not, then … Well, the big ones, the ones that cause global problems, are the easiest ones to find. And that is NASA’s goal now, to find the ones that are larger than a kilometer. We’re doing well, actually: We’re up to 807 out of a total population of about 1,100 asteroids of that scale.

Once we find them, they’re no longer a problem, because we can track them for 100 or 200 years in the future, and keep an eye on them. None of them are a problem, but it’s the smaller ones — and there are hundreds of thousands of them  that we haven’t been able to deal with yet, because we don’t have the telescope apertures yet.

And I suppose there’s also an issue with long-period comets, as well as asteroids that spend almost all their time inside Earth’s orbit. Those are some of the things that are mentioned as “out-of-the-blue” threats.

That’s true. There are the Atens, the objects that spend most of the time interior to Earth’s orbit. They are difficult to find, because they don’t appear in darkness very often. There is at least one NASA program that is looking as close to the sun as possible to find those, and they’ve found a few.

INTERACTIVE Below the belt Learn about close encounters of the asteroid kind

You mentioned the comets. Now, they’re the wild cards. The bad news is, if they come in from the outer solar system, they don’t start outgassing until they get well inside the orbit of Jupiter, and thus don’t show themselves. It only takes 9 months to get from Jupiter’s orbit to Earth’s orbit. So that’s the bad news.

The good news is, in terms of numbers, there are 100 times more asteroids than comets in the near-Earth space. So asteroids are really the major problem, and we can deal with them. Comets are 100 times less of a problem, in terms of numbers, and we can’t really deal with them anyway at the moment. So we’re concentrating on the asteroids at the moment.

It would take a lot more highly developed technologies to discover comets early enough to do something about them. We’d have to have sensors out beyond the asteroid belt, near Jupiter’s orbit, looking for these things. And even if we found them, the orbit determination at that distance would be so poor, we couldn’t predict precisely whether they would be a threat until they got in a lot closer anyway. So at the moment there’s no clear path for dealing with long-period comets. But they’re a 1 percent problem, compared to the 99 percent problem of the asteroids.

Could you refresh my memory on missions to near-Earth objects that are in the works? I know that Japan’s Hayabusa mission to bring a sample back from an asteroid is nearing its climax, and then there’s the European Rosetta mission.

Hayabusa is an interesting mission. Their target body, Itokawa, is a near-Earth asteroid that’s representative of the type of asteroid that would most likely be a problem. The structure of the object looks like a rubble pile, but the bulk density is not unlike Eros, which means it’s not completely all rubble held together by its own self-gravity.

You mentioned Rosetta, which will set down on the surface of a comet in another few years. I think that’s about it, unless Deep Impact gets a follow-on to another comet. And of course there are several Discovery proposals in the works for comets and asteroids, but they haven’t been selected as yet.

It sounds as if Apophis itself might be a candidate for a Discovery mission someday.

Well, that’s the thing with near-Earth objects: Many of the ones that represent the largest potential threats are also the easiest ones to get to, because they’re in very Earthlike orbits. So the rule of thumb is that the more Earthlike an object’s orbit is, the easier it is to get to. So it’s one of the easiest objects to reach in terms of a rendezvous mission. It does make sense, to me anyway, that somebody would suggest this as a Discovery mission. We could put sensors on board the asteroid, and watch the asteroid perhaps readjust itself as it flies by in 2029.

It’s going to be a naked-eye object. It’s going to go underneath geosynchronous satellites. I mean, it’s going to be quite a show. You could engage the guy on the street rather well with this mission. … That object, to my mind, is less of a threat and much more of interest for scientific purposes and engaging the public in this issue. So I think this is an opportunity that we shouldn’t pass up.

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