But if this whole huge region is hospitable for Martian microbes, then the accidental contamination of one local site by Earth germs - some of which are very likely to find the subsurface Martian environment hospitable - would be free to spread around much of Mars; extremely slowly, but unstoppably.

All such drilling operations - manned or unmanned - will have to include extreme precautions.

The other - more obvious - problem is what to do about manned expeditions to Mars.

It is, of course, flatly impossible to sterilize a manned ship - every time the airlock opens it will puff out clouds of Earth germs onto the Martian landscape; the sewage and garbage will be rife with them no matter how carefully it is processed; and even the most airtight spacesuit spews air containing thousands of germs per minute out of its seams.

Every time a manned expedition lands on Mars, it will quickly contaminate the very Martian material it is trying to examine for evidence of life.

The same two problems I've mentioned before - local contamination of surface sites and the very samples taken from them, and the possibility of more widespread contamination of the underground Martian water table - will be far more severe for manned landings than for unmanned ones.

So severe, that the Space Studies Board of the National Academy of Sciences has said that "It is... critical that a major effort be made to determine whether there are places in local Martian environments, such as active hydrothermal areas, where life might plausibly survive, and to more closely examine these areas robotically, before contamination by humans occurs."

And it made this statement in 1992, before it was apparent that underground Martian life might perhaps be widespread.

It is possible that when humans first travel to Mars, international agreement may require that it be a long time before they actually land there. And that initially the astronauts stay in orbit around Mars or on one of the Martian moons, operating complex robotic exploration equipment by remote control.

This will avoid the problem of the very long radio signal time delay from four minutes up to a half hour that makes exploring Mars by remote control from Earth so difficult.

Carefully sterilized vehicles could rocket samples from the Martian surface up to labs on such manned orbiting scientific stations, or all the way back to Earth. For a long time, Mars may be humanity's biggest nature preserve.

Onward To Europa

Then there is the second world in the Solar System where it is thought that there is a serious chance of past or present life: Jupiter's moon Europa, which may have a liquid-water ocean underneath its kilometers-thick ice crust that could perhaps be capable of sustaining bacterial life even today - and which certainly had such an ocean in its warmer early days, so that the remains of ancient Europan life may be frozen into the ice in large amounts even if no liquid water exists on Europa today.

The forward-contamination problem is less serious on Europa because that world is so effectively sealed by its ice crust, and because Jupiter's intense radiation belts will sterilize anything on Europa's actual surface in a matter of minutes.

We can dig around in that solidly frozen ice to a very substantial degree without fear of contaminating anything beyond the immediate ice we are touching - and it will be a very long time (if ever) before men land on Europa.

But if our early spacecraft confirm that a subsurface ocean still exists, our later plans call for unmanned vehicles to melt all the way through that thick ice crust into the underlying ocean to investigate it - and we will, once again, have to be extremely careful to make sure that such vehicles are sterilized, since Earth germs would spread even more quickly and inevitably in an ocean than they would in the Martian water table.

NASA plans to rehearse such sterilization procedures during the next few years when it (in collaboration with Russia) begins drilling into "Lake Vostok" - a huge lake of liquid water as big as Lake Ontario, recently discovered four kilometers under the ice of Antarctica, which it is eager to investigate for signs of ancient isolated species of bacteria, and which also makes an excellent testbed for the kinds of subterranean ice probes that will be used later on Europa.

And we will still have to take some precautions even when we are digging samples out of Europa's frozen upper ice layers. There is a strong suspicion that subsurface eruptions of liquid water into Europa's upper ice from below still occur occasionally; and, if so, they could spread local pockets of frozen hibernating Earth germs to other areas of the Europan ice crust, where they could later revive and multiply when gifted again with liquid water.

For all these reasons, the National Academy of Sciences already has a team carrying out a study of the best ways to avoid contaminating Europa, which is due to be completed next year.

The same considerations apply to any other ice-covered moons in the outer Solar System, such as Ganymede and Callisto, where a subsurface liquid-water ocean may exist - although the chances that any other such worlds could ever have supported life is remote because of their lack of the proper chemical energy sources for such microbes.

If multicellular life - any life more complex than microbes - existed on Mars or Europa, our ethical responsibility to avoid contaminating those two worlds would obviously be tremendously increased.

But - for reasons I hope to detail in a later article - there is virtually no chance that non-microscopic life exists on either world today. Although Dr. Christopher McKay has given reasons for thinking there is a small chance that it might have had time to evolve on early Mars before becoming extinct as the planet lost its supplies of air and surface liquid water.

Nevertheless, we do have responsibilities. And, as I've said, I have a suspicion that the discovery of present or past life on Mars - the one thing that could make a manned scientific expedition to that planet urgent - would, ironically, also act to substantially delay the date on which humans actually first set foot on Mars.

Click For Part One

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TERRADAILY

Mars Invades Earth
Cameron Park - June 4, 2001
In the wake of the latest report on preparing for samples from Mars, the old arguments for and against have again taken center stage in this perennial debate. The basic argument against returning Mars samples is that the chances that "extant" (that is, still-living) microbes still exist on Mars are higher than NASA is making out, and that there is a genuine and serious chance that such microbes might prove harmful to Earth's biosphere -- and perhaps to human beings themselves. How accurate is this?

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