Contamination From Mars: No Threat

Of all the dragons infesting the maps of would-be Mars explorers, one stands out as not only illusory but hallucinatory. This is the "Threat of Back Contamination."

The story goes like this: no Earth organism has ever been exposed to Martian organisms, and therefore we would have no resistance to diseases caused by Martian pathogens. Until we can be assured that Mars is free of harmful diseases, we cannot risk exposing a crew to such a peril, which could easily kill them or, if it didn't, return to Earth with the crew to destroy not only the human race but the entire terrestrial biosphere.

The kindest thing that can be said about the above argument is that it is just plain nuts. In the first place, if there are or ever were organisms on or near the Martian surface, then the Earth has already been, and continues to be, exposed to them.

Over the past billions of years, millions of tons of Martian surface material have been blasted off the surface of the Red Planet by meteorite strikes, and a considerable amount of this material has traveled through space to land on Earth. We know this for a fact because scientists have collected tens of kilograms of a certain kind of meteorites called SNC meteorites and compared the chemical composition of the rocks' entrapped gases with the atmosphere measured on the Martian surface by the Viking landers. The perfect match between the two represents an irrefutable fingerprint proving that these materials originated on Mars.

Although each SNC meteorite must wander through space for millions of years before arrival at Earth, it is the opinion of experts in the area that neither this extended period traveling through hard vacuum nor the traumas associated with ejection from Mars and arrival at Earth would be sufficient to sterilize these objects, if they originally contained bacterial spores. Furthermore, on the basis of the amount of SNC meteorites we have found, it has been estimated that these Martian rocks continue to rain down upon the Earth at a rate of about 500 kilograms (more than 1,000 pounds) per year. So, if you're scared of Martian germs, your best bet is to leave Earth fast, because when it comes to Martian biological-warfare projectiles, this planet is smack in the middle of torpedo alley.

The fact of the matter is that life almost certainly does not exist on the Martian surface. There is no liquid water on the surface-the average surface temperature and atmospheric pressure will not allow it. Moreover, the planet is covered with oxidizing dust and bathed in ultraviolet radiation. Both of these features-peroxides and ultraviolet light- are commonly used on Earth as methods of sterilization. If there is life on Mars now, it almost surely must be ensconced in exceptional environments, such as heated hydrothermal reservoirs underground.

But couldn't such life, if somehow unearthed by astronauts, be harmful? Absolutely not. Why? Because disease organisms are keyed to their hosts. Like all other organisms, they are specially adapted to life in a particular environment. In the case of human disease organisms, this environment is the interior of the human body or of a closely related species, such as another mammal. For almost 4 billion years, the pathogens that afflict humans today have waged a continuous biological arms race with the defenses developed by our ancestors. An organism that has not evolved to breach our defenses and survive in the microcosmic free-fire zone that constitutes our interiors will have no chance of successfully attacking us. This is why humans do not catch Dutch elm disease and trees do not catch colds. Any indigenous Martian host organism would be far more distantly related to humans than are elm trees.

There is no evidence for the existence of (and every reason to believe the impossibility of) macroscopic Martian fauna and flora. Without indigenous hosts, the existence of Martian pathogens is impossible. And if there were hosts, the huge differences between them and terrestrial species would make the idea of common diseases an absurdity.

Equally absurd is the idea of independent Martian microbes coming to Earth and competing with terrestrial microorganisms in the open environment. Microorganisms are adapted to specific environments. The notion of Martian organisms out-competing terrestrial species on their home ground (or terrestrial species overwhelming Martian microbes on Mars) is as silly as the idea that sharks transported to the plains of Africa would replace lions as the local ecosystem's leading predator.

Not too long ago, I took part in a NASA planning meeting for the upcoming (robotic) Mars Sample Return mission, during which someone seriously proposed that, to allay alleged public concerns, any sample acquired on Mars be sterilized by intense heat before being brought to Earth.

While an extremely unlikely find, the greatest possible treasure a Mars Sample Return mission could provide would be a sample of Martian life. Yet certain of those attending the meeting would destroy it preemptively (and a great deal of valuable mineralogical information in the sample as well). The proposal was so grotesque that I countered by asking the assembled scientists, "If you should find a viable dinosaur egg, would you cook it?"

The question is not entirely out of line; after all, dinosaurs are our comparatively close relatives, and they did have diseases. In fact, every time you turn over a shovelful of dirt, you are returning a sample of the Earth's disease-infested past to menace the current biosphere. Nevertheless, paleontologists do not wear decontamination gear.

Just as the discovery of a viable dinosaur egg would represent a biological treasure but no menace, so a sample of live Martian organisms would be a find beyond price but certainly no threat. By examining Martian life, we would have a chance to differentiate between those features of life that are idiosyncratic to Earth and those that are universal. We might be able to observe organisms simpler than bacteria, missing links in the evolution of life from a chemistry whose simplicity could clarify our understanding of the structure and functions of more complex organisms. We could thus learn something fundamental about the very nature of life. Such knowledge could provide the basis for astonishing advances in genetic engineering, agriculture, and medicine.

No one will ever die of a Martian disease, but it might be that thousands of people are dying today of terrestrial ailments whose cure would be apparent if only we had a sample of Martian life in our hands.

Back contamination mavens need to back off. Their warnings have no rational basis and are being used to urge crimes against science.

Robert Zubrin, President of the Mars Society, made his reputation as a cutting-edge planner of solar-system exploration while at Lockheed Martin Corporation. He is the founder and CEO of Pioneer Astronautics and author of two books: The Case for Mars (Simon and Schuster, 1996) and Entering Space (Tarcher-Putnam, 1999).

A Case For Caution - by John Rummel, Ph.D., Planetary Protection Officer, NASA Headquarters

Practice Safe Science - Kenneth H. Nealson, Director of the Center of Life Detection, NASA/JPL

a href="http://www.planetary.org/html/news/comments.htm#contamination">Readers comments

The environmental wackos are now trying to protect space, and protect us from space.

They couldn't care less about protecting us. But they've been squalling for years about keeping Space (note the capital) free and open for all species.

Expect their noise to increase during the Bush administration. SecDef Rumsfeld is a big proponent of using space for defense. The envirofools and assorted libs and commies will screech that this militarization of space is evil (ignoring the fact that the Chinese tested a satellite killer - in space - several years ago).

"...But couldn't such life, if somehow unearthed by astronauts, be harmful? Absolutely not. Why? Because disease organisms are keyed to their hosts. Like all other organisms, they are specially adapted to life in a particular environment..."

This is generally true, however there is always a residue of uncertainty. If the Martian organisms were functionally similar to Earthly lifeforms there would be an admittedly remote possibility of sufficient 'overlap' in metabolic processes to allow them to produce disease.

Even functionally dissimilar organisms could not be automatically assumed to be 'safe'. Although the likelihood is vanishingly small, there would still be a possibility that an utterly alien life process could produce the biological equivalent of 'Unintended Consequences' if Earthly life was exposed to it.

Assuming that cross-contamination of organic materials (and even primitive life forms) has occurred between Earth and Mars the possibility of finding at least primitive functionally similar life there increases.

Fortunately, the odds would also increase that Earth's and Mars' 'cousin' life forms would be at least partially adapted to one another, and that both groups would have the ability to muster at least some degree of immune response to the other.

Utterly alien life, on the other hand, would have the (admittedly remote) chance of possessing, purely by chance, a chemistry that is in some unpredictable manner reactive with Earthly life. The reaction might easily be equally destructive of the alien life causing it but that would be little comfort to life on Earth if contact with that alien life were to precipitate a self-sustaining reaction. Since there would be no shared biological ‘history’ between the antagonistic life processes, there would be no moderating effect of natural selection to cap lethality at sustainable levels. Such a plague could explode with geometric rates of infection and literally sterilize an entire biosphere in a very short period of time.

In the absence of comprehensive methods to simulate the incredibly complex interactions that might occur between radically different life forms the only ‘sure’ method would be to expose a cross-section of the human population to the alien life form and then observe what happens.

Certain classes of condemned criminals might be allowed to volunteer for such an experiment, and earn remission of their punishment by providing this service to mankind. Communists might also be used in situations where volunteers were not forthcoming when and where needed.

Of course, in cases where communists were used, it would only be natural for the researchers to be hoping for a little ‘bio-drama’ to unfold on the other side of that foot thick porthole...

"...Again emotion mascarading as science. Life is full of risk, and exploration even more so. that doesn't mean that you throw caution to the wind, but it does mean that you don't let your fears paralyze your efforts to explore..."

Don't misunderstand my comments. I believe that we should have already established the first permanent human settlements on both the Moon and Mars at this point in history. (We chose instead to deep-six a trillion wasted dollars into the ghettos.)

Man’s spirit of exploration will not be forever denied, however, and when we do finally move outward from Earth, we must maintain an effective biological firewall between us and the frontier. We will encounter nasty surprises there.

While I also estimate the risks to be minimal, I do not think them non-existent. Just because life (if any) on the surface of Mars must occupy a drastically different environment, it is not shown that such conditions are prevalent below the surface. Life, especially microscopic life, is incredibly robust, and as we don't even know what dormancies exist on earth, we are hardly likely to be able to anticipate accurately for conditions of which we are presently entirely ignorant. Could, at some point, there be a commonality of conditions somewhere in time between the two planets, but within dormancy, sufficient to present a risk of an organism being able to exist in both environments? It isn't outside the realm of possibility, albeit unlikely.

So I'd suspect normal containment precautions will be sufficient, and probably excessive. No reason for paranoia, but no reason to discard safe scientific practice either.

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