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Chance for a Tunguska Sized Impact on Mars
Multiple users have written to tell us of an LA Times report that an asteroid may hit Mars on January 30th. The asteroid is roughly 160 feet across, and JPL-based researchers say that it will have a 1-in-75 chance of striking Mars. Those odds are very high for this type of event, and scientists are hoping to witness an impact of a similar scope to the Tunguska disaster. From the LA Times:
"Because scientists have never observed an asteroid impact -- the closest thing being the 1994 collision of comet Shoemaker-Levy with Jupiter -- such a collision on Mars would produce a 'scientific bonanza,' Chesley said."
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Caesar si viveret, ad remum dareris.
Even if it misses it should still be a little interesting. If it comes that close, its orbit will be greatly affected, observing the results should be useful?
If the asteroid does hit the impact site would probably make for a good rover mission. Fresh samples of long buried rock without the extra hassle of having to dig it up!
Murphey's fighting Occam, and we're in the stands.
Even if it did, what we would learn would make it a more than fair trade. The mars rovers have done exceptionally well, but they won't last forever anyway. Its time to start thinking about the next generation of rovers, and manned missions back to the moon & to mars.
Also, the massive publicity if there was a hit, with the sorts of pictures NASA would get would hugely increase public interest and support in making sure we can predict early enough and prevent the same thing never happens here.
The received wisdom used to be that the meteorite, that caused the disaster in Tunguska, exploded above the surface of the earth. It entered the atmosphere at a relatively shallow angle and heated up much more than it would have if it had come straight down. The result was that a long relatively narrow area of forest was knocked down and there was no impact crater.
On Mars, the atmosphere is much less dense than that of the earth. The meteor in question is large. If it hits Mars, it will reach the surface, it won't vaporize in the atmosphere. The result will be much more like other impacts on the earth that did leave craters. In that light, the comparison with Tunguska doesn't make much sense. I don't know where Steve Chesley got his information on the size of the rock that exploded over Siberia but I bet it wasn't 160 feet across. Something that size would make it to the Earth's surface.
The Tunguska asteroid exploded in the atmosphere, it did not hit the ground and raise dust.
If 2007-WD5 hits Mars it will probably not explode in the thin atmosphere but impact Martian soil and raise huge amounts of dust. Martian dust is fine-grained and lightweight, and can raise high in the atmosphere - as we have seen during the dust storms. So I guess the dust plume would not stay localized, and it could mean trouble for the rovers and even for the Phoenix-lander.
On the other hand the impact-crater would be very interesting to probe!
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The nuclear winter is a concept that works only on Earth due to our unique atmosphere which lets a bit of sunlight in and prevents a bit of that from radiating out, thus warming our planet. If our atmosphere grew a bit more dusty, we'd reflect more sunlight and become colder.
You cannot apply this concept to Mars, which has no greenhouse effect in the first place. Its surface reflects most of the sunlight already, so reflective dust in its thin atmosphere would make no difference. You also can't apply it to Venus, which is a greenhouse. Its atmosphere is already highly reflective, and it is only as hot as it is because the tiny amount of sunlight it absorbs is prevented from escaping.