[X] My Assistant

[rogelio]

http://www.latimes.com/news/science/la-sci...=la-home-center

[ugordan]

One, the nuclear bomb-type "mushroom cloud" looks like what I would expect of a small impact on any planet with an atmosphere (i.e., Earth or Mars). The other looks like virtually all textbook illustrations of impacts, and shows the early-formed ballistic ejecta curtain only. It is what I might expect for impacts on the Moon or other planet with no atmosphere (although even there the rocks themselves are vaporized, at least ephemerally).

I myself am very interested in how a convective updraft cloud would behave in a low-density atmosphere. On Titan I'd expect a mushroom cloud very similar to one on Earth, varying in head/stem dimension, but it would be interesting to see how one would look on Mars. For one, the buoyancy would be greaty reduced, also reducing the updraft which creates the characteristic mushroom stem. The two artistic views could be regarded as the same scenario - mine would be the initial impact (I was actually aiming at that) throwing ejecta up and Stu's would be the aftermath several minutes later when ejecta has settled down and the dusty "fireball" rose up and cooled down.

I believe the initial moments of an impact that couples energy to the ground well (something surface-detonated nuclear weapons don't do well, in addition to releasing over 50% energy as thermal, not kinetic) would be dominated by the ejecta blanket, screening the (small) incandescent fireball at the point of impact.

Here's a not-so-good analogy with ground penetrating weapons: http://www.youtube.com/watch?v=KF8gnokHrWw (Caution: VERY LOUD!)

There are better videos out there, but I can't seem to dig them up now.

Would you really like Opportunity to be anywhere near this shower of debris (and note Mars' thin atmosphere would basically allow ballistic emplacement of debris)? I know I wouldn't...

Here's a more classical fireball on the other hand, typical of atmospheric nukes, not resulting in large excavation as much as a large fireball and atmospheric shockwave: http://www.youtube.com/watch?v=PwuMdNg9oWQ (ignore the F-words)