Greg,

As I think Nick implied it is quite possible for Martian life to live too deep to be transported by meteorites. However, Barry contends that Martian life exists at the surface based on LR results, that surface samples could be a huge hazard, and that cross-contamination on the surface is a huge issue for manned missions. The last two claims look doubtful if we are likely to be reciving surface samples from Mars in an uncontrolled manner on a routine basis and Barry is correct that surface life is common. Barry's contradictory attempts to link mass extinctions to panspermia while denying life could be transferred from Mars to Earth overlooks the frequency at which these transfers are likely to occur. If Martian microbes caused mass extinction and a Martian meteorite capable of transporting life lands every month it is unlikley that the transfer would be viable only once every 30 to 100 million years and we know such a transfer was not responsible for the last major extinction.

I have posted several links indicating you don't need anything like Hellas size impactors to send material from Mars to Earth. Now as you point out the samples we have could simply have come from barren areas. However, impacts as a whole are random and will not be restricted to sterile areas unless the whole surface is sterile. Most meteorites are not recovered so the samples we have can in no way be construed to represent the frequency of Martian meteorite impact. meteorites. Evidence has been presented clearly indicating that the interior of ALH84001 never got hot enough to sterilize Earthly microbes so you can not blame lack of life on "melting". Plenty of data indicating it can get here from there has been posted recently. There is no reason to conclude it can't based on that evidence. We can't prove absolutely that it can until an obviously alien living sample is recovered from a meteorite, but we have good reason to believe it could IF it was in the meteorite to start with.

It is possible that Martian life does exist near the surface in only a few isolated areas greatly reducing the chances that any Martian meteorite would contain life. You still have the issue that wherever there is surface life on Mars it could be transferred to Earth via meteorite based on the best data we currently have available. Benton Clark and other astrobiologists make the point that we still need to be careful with MSR because we will be transporting a sample more rapidly from Mars than likely by impact and we will be selectng places most likely to contain evidence of life. I agree with that point. What I don't agree with and what most astrobiologists don't agree with is that the likelihood of risk is high enough to warrant the orbital facility Barry wants. It's not just a matter of hazard either. It also comes down to the practical issues of long term containment and risk of failure. Orbital Rondevouz will be difficult and could fail with the capsule reaching Earth anyway resulting in greater odds of contamination than if the mission was designed for Earth return. The ISS and any other orbital facility will not stay in orbit forever and will eventually pose a contamination risk.

Regards,
Mark