[X] My Assistant

[JRehling]

Walking the line between wacky and sure to be unoriginal:

The martian meteorites are quirky in the ages, in that about half of them have ages of roughly 175 million years, whereas most of the martian surface is clearly older than that. There must be a selection effect biasing the samples we find.

Is it possible that altitude (on Mars) is a major selection factor? The top of Olympus Mons is above 90% of Mars's atmosphere. Of course, that represents a very small fraction of the surface area of Mars, but when you add in the heights of the five biggest volcanos on Mars, you get a still small but nonzero area of the surface of Mars at high altitude AND likely to be the last places on Mars to get paved over with lava.

When an impactor strikes these areas, it faces much less air resistance (and spalling) on the way in, and then any ejecta flying skyward also faces much less air resistance on the way out.

Additionally, sheets of lava should make for more elastic collisions than the dusty regolith at lower altitudes.

Could it be that these selection effects favor the highest volcanos so greatly that ejecta from these places outnumber ejecta from the rest of the surface combined?

[tty]

Perhaps Jay Melosh at the University of Arizona?

http://www.lpl.arizona.edu/faculty/melosh.html

[marsbug]

Perhaps Jay Melosh at the University of Arizona?

http://www.lpl.arizona.edu/faculty/melosh.html

If it hasn't been run across already, this article, reproduced from Melosh's contribution to the july 94 planetary report, has some interesting ideas that might apply to a mars impact, particularly in the updates down the bottom where he talks about how spallation might not operate alone to launch particles , but in combination with the impact plume.