[X] My Assistant

[nprev]

Here's a Christmas present for us all...a 0.7 km NEO may make a 4200 km altitude Earth flyby on Halloween, 2041: http://neo.jpl.nasa.gov/risk/2006xg1.html

[nprev]

Yeah, I'm sure that will be the case. I noticed that the NASA NEO site already had 76 observations logged between 11-22 Dec; it must be very favorably placed, so we should see it drop off the radar screen after the holidays.

Good thing, too. 1900 megatons of impact energy could be a bit unpleasant. With that in mind, does anybody think that we should get serious about devising a way to deflect these things, if it's ever needed? I like the idea of "docking" a DS1-style propulsion system to a threatening rock & steering it clear...or, ideally, steering it slowly into an exploitable orbit for future mining!

And on a somewhat related topic, is there anything at all we could do about an imminent long-period comet impact? I can't think of a single countermeasure. (Okay, I confess...I rented the classic When Worlds Collide two days ago, and it's been bugging me ever since... )

[tty]

And on a somewhat related topic, is there anything at all we could do about an imminent long-period comet impact? I can't think of a single countermeasure. (Okay, I confess...I rented the classic When Worlds Collide two days ago, and it's been bugging me ever since... )

I agree that the "gravitational tug" concept is the most promising when there is plenty of time to deflect an object. In the cometary case where only months may be available an Orion-style deflection using nuclear charges is probably the only remotely feasible method.

tty

[nprev]

I agree that the "gravitational tug" concept is the most promising when there is plenty of time to deflect an object. In the cometary case where only months may be available an Orion-style deflection using nuclear charges is probably the only remotely feasible method.

tty

...and even then we'd probably have to try to severely fracture the nucleus al a Lucifer's Hammer in order to disperse the terminal impact energy. However, the Stardust results are kind of scary in this respect: at least some comets may be pretty mechanically solid instead of just big snowballs as we've assumed for many years...

On the lighter side, per the NASA NEO site 2006XG1 now has 99 observations under its belt, miss distance is now 0.72 Earth radii, the Palermo rating has decreased (good) as well as the estimated impact energy, and the sigma LOV now indicates much less certainty re the close-encounter trajectory: http://neo.jpl.nasa.gov/risk/2006xg1.html

[JRehling]

I wonder if a good long-term defense would be to try to give the Earth some Phobos-class satellites diverted into elliptical orbits from the asteroid belt. Then stop an incoming impactor by moving the blocker into the way. The advantage is that you wouldn't have to launch any "solutions" out into solar orbit all of a sudden as the threat arose. Disadvantages abound, of course, including debris from the pre-collision and the threat of just plain missing.

The "push" strategies for dealing with a short-period threat, of course, leave the menace there to eventually swing back towards Earth after decades or centuries. A strategy for dealing with those would be to push them into the Moon.

[ugordan]

Then stop an incoming impactor by moving the blocker into the way.

Apart from the nasty possibility of missing you mentioned, the biggest problem I see with this scenario is how a Phobos-style moon would absorb the hundreds or thousands of megatons of impact energy. It seems such an energy density is way too much for a small body of an order of 20 km in diameter to structurally hold it together. Whether the moon be a rubble pile or a solid rock I'd expect it to simply blow up. Spectacularly. Then you get many smaller projectiles (say several meters diameter) possibly spraying back on Earth. That's still at least kilotons of energy per fragment, not something you want to be at the receiving end of.