Hi Marcia -

oh christ, yet even more "good news" from Rio Tinto - now our future mars explorers will not only have to face sulfuric acid, but possibly live organisms as well -

as regards the polygons, see my note above to Nick -

the glassy spheres on Earth that you note are more likely products from the entry of fragments of Comet Encke into the atmosphere, rather than the result of oceanic impacts. While oceanic impacts occured during some of these encounters (for the exact dating of which see the Cambridge Conference archives), I don't think that the physics of these impacts produce the glassy spheres - but who knows? In several of these cases, you are likely to find mixed types of spheres, each type formed by a different part of the impact process.

By the way, remember that a chunk of Carbonaceous Chondrite (i.l. dead comet) was recovered at the KT layer - while Morrison may insist that the impactor was an asteroid, that does not mean that what hit was. The "debate" here is going to be sharp, and I intend to stay away from it; that said, the observed periodicity strongly argues against Morrison's position. The Cassini data are going to decide this issue, and that's how it should be - no point in being wedded to a premature hypothesis when definitive data is soon to become available

In any case, the use of man tended Moon based systems are the optimal way of handling this hazard.

The martian "berries" are larger than the glassy spheres. I can't picture them as entry products, even for tangential impacts - I suppose its a question of the density of the molten vapor produced.

By the way, have I mentioned before that the ESA mars rover will likely use an autonomous robotic vision system?

have a good one -
ep