[X] My Assistant

[remcook]

http://www.timesonline.co.uk/article/0,,2089-1697332,00.html

FAR from discovering life on Mars, Nasa may have put it there. The American space agency believes the two rover spacecraft scuttling across the red planet are carrying bacteria from Earth, writes John Harlow.

Probably isn't the first time either. Can't believe old russian probes had any policy with that respect.

[tedstryk]

I think that the big reason that the contamination of Mars is a big deal is that it is possible that life evolved on its own there. Also, it might have naturally transmigrated via meteors and taken hold there. Unlikely, but possible. Contaminating it via spacecraft might lead to a situation in which we will never know if the life we are studing, should we find it, came from Earth via meteors, is indigenous to Mars, or was carried by our own missions. Thus, it is a big deal. This recent story however isn't. This did not come from the scientific community, but an author shamelessly trying to promote his book, and a hapless journalist who fell for it. Also, wouldn't it be tragic to find the remains of dead martian bacteria, and to discover that its end was brought about by agressive bacteria brought by us!

[dvandorn]

Well, yes -- introducing strains of bacteria that are more successful than native Martian bacteria, up until the point where you've learned as much as you can from the native stuff and preserved it in laboratories and protected zones, is not a good idea.

But consider -- it is really, really unlikely that present-day Martian bacteria live anywhere near the surface of mars. Especially not near enough to the surface for any of the chicken-scratchings our probes have made to get anywhere close to it.

It's been mentioned that the real threat would be for terrestrial organisms to find nutrient-rich environments (which, I will add, must be protected from the surface radiation environment) and overcome any native forms. And I ask, with all sincerity -- just where would one find a nutrient-rich and radation-protected environment near enough the surface of Mars to allow terrestrial bacteria to move from a landed probe into them? And remember, the radiation environment at the surface is a pretty good sterilizer -- any transport mechanism you postulate would have to figure out how to get terrestrial organisms to the protected environments quickly, before the radiation environment destroyed them.

I would be fascinated to hear about any theories of such a transport mechanism that don't depend, at some point or another, on the infamous "and then a miracle occurs" step in the process...

-the other Doug

[djellison]

it is really, really unlikely...

But not impossible

Doug

[dvandorn]

No, not impossible -- but such life would have to have developed protections against the radiation environment that would make it vanishingly close to impossible that any terrestrial life form *not* adapted to the radiation environment would be capable of competing with it. Or even capable of surviving.

I always liked the way Mike Collins referred to the extra-terrestrial contamination issue. Of course, he was referring to the remote possibility that lunar materials might pose a threat to the Earth's biosphere, but his remarks apply here, as well.

Collins said that if you take the possibility of a profound threat from contamination by extra-terrestrial organisms (very, very small) and multiply it by the potential damage such contamination can cause (very, very large), you come up with a reasonable number that defines how much attention you give to the problem.

Now, when we start sending probes to dig more than a foot or two into the Martian soil, I think we need to take special care to sterilize any part of the spacecraft that reaches into a realm where terrestrial organisms could survive. But until then, I think the present sterilization procedures (which make the possibility of carrying significant amounts of terrestrial life to Mars very, very unlikely) makes the first part of Collins' equation a very small number. As long as that number remains very, very small, I think the risks of continuing to explore the surface of Mars are acceptable.

Besides, unless we're willing to take the risk, we'll never know whether or not there is any Martian life that needs protecting. Like I said, observing something affects it. And human technology is not infallible, so it is impossible to guarantee that all Mars landers will be *completely* free of terrestrial organisms. You *must* risk some small contamination possibility just to find out if there is any Martian life out there that could be at risk. If you insist on the presence of Martian life, and if you further insist that even a single bacteria carried to the surface will *definitely* contaminate or even destroy that life, then you're forced into the position that we must immediately cease *all* exploration of Mars. Including orbital exploration (since orbiters eventually crash). And you have to admit that your worst fears must already have been realized, since we've already landed and crashed imperfectly-sterilized craft on Mars.

Since we can't even *guess* at where life might presently exist on Mars, or under what conditions it may flourish, we have to do a lot more exploring there, including many more landings and even sample-return missions, to *ever* expect to find it. If it exists. Insisting that even the *possibility* of life on Mars means that we must stop *all* possibility of contaminating it means that we'll never, ever know if that life exists or not.

The most important thing about finding life on other worlds is to see if it organizes in different forms and with different chemical compositions than life does on Earth. If we dare not even go look for it, we'll never have the opportunity to even ask those questions, much less expect to get answers.

-the other Doug