Jacob Samorodin asked:

>...what did JPL engineers learn from those images
>returned by Opportunity of its smashed heatshield?

The main consumers of those heat shield pictures wer Lockheed-Martin (they actually manufactured the heat shield). The inside of that heat shield had lots of numbers printed on it that were used as manufacture control numbers. They could look at a fragment on the martian surface and often times see one of those numbers. They could then reconstruct where the fragment came from in the heat shield's pre-impact geometry. They could then back out how it actually struck the martian surface and broke up. Some of us were hoping that we learn something about surface recession and pyrolysis depth but the heat shield was too beatup for that. A big issue was a dynamic instability that appeared in MER's angle-of-attack while it was still going hypersonic. At one point it was having angle-of-attack excursions of over plus-and-minus 10 deg. (it should have been about a third of that). Apparently there was a seal between the forebody heatsheild and the backshell that got out from between the interface gap and was flapping in the breeze. That seal is believed to have caused the angle-of-attack excursions. Supposably they saw this seal sticking out on some of the heat shield wreckage thus giving them a warm-and-fuzzy feeling about the theory.

>As far as Mars surface being perfectly sterilizing?

The phrase: "the martian surface is almost a perfect sterilizing environment" is almost a direct quote from Lynn Margulis (google her). She knows a heck of alot more about biology than anyone on this board including me. There are strongly oxidizing chemicals in the martian regolith (we know there was/is sulfuric acid mixed in with the regolith at Meridianni). Of course there are micro-organisms that like sulfuric acid, e.g. archaea. However you then add to the mix that secondary cosmic rays and hard UV are reaching the martian surface. Also surface temperature is usually below freezing and the vapor pressure is below water's vapor pressure. All of this combined leads to the reasonable conclusion that the martian surface is sterile. Of course all bets are off if you go deep underground on Mars. Nick Hoffman and others can make good arguments about "deep dark life". However if Mars has always been frozen with a thin atmosphere then the argument that some sort of genesis condition once existed on Mars becomes a stretch.

I should mention that a Mars with a sterile surface but a potentially viable underground might(?) actually be the best scenario. A hypothetical Mars with active surface biology is almost impossible to study due to planetary contamination issues. It's almost impossible to design a sample return under that scenario without the cost being ridiculous. However a hypothetical Mars with deep underground life is easier to sell politically as an exobiology exercise versus an exercise in straight science. IMHO, a Mars program based upon straight science is more intellectually honest than exobiology but then again I don't hold the purse strings.

Gary