http://www.planetary.org/html/news/opinions/nothreat.html

Contamination From Mars:
No Threat

by Robert Zubrin
from the July/August 2000 Planetary Report

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 Habitat Needs of Germs
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.

Sterilized Samples: A Terrible Loss
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).

Here is a response to Zubrin's comments by John Rummel, Ph.D., Planetary Protection Officer, NASA Headquarters :

http://www.planetary.org/html/news/opinions/caution.html

A Case for Caution
(in response to Contamination from Mars: No Threat)

by John D. Rummel
from the November/December 2000 Planetary Report

There are days when I ask myself, "Is it worth it?" After all, given the heightened awareness about Earth organisms and their newfound capabilities in extreme environments-to say nothing of the troubles that immune-compromised patients face with normally benign microbes-I figure the need for back contamination controls for missions to places possibly harboring life should be obvious. So I sometimes wonder if I, as Planetary Protection Officer, can really make a difference.

I want to thank Bob Zubrin for providing this week's job satisfaction. His opinion piece in the July/August 2000 issue of The Planetary Report was so off the mark that I found renewed joy in simply contemplating an answer. And I found it an interesting coincidence that David Jewitt's piece in the previous issue of The Planetary Report ("Astronomy: Eyes Wide Shut," May/June 2000) was introduced in the table of contents with the statement "It's always easy to make fun of things you don't understand. It's always easy to ignore threats when they have not yet loomed above the horizon." Of course, Zubrin has done just that with straw-man arguments placed for his own convenience. I very much admire Bob for his contributions to Mars exploration planning, but in this case he should know better.

First off, the potential for back contamination-that is, bringing organisms back to the Earth from Mars missions-depends on the potential for a solar system body (such as Mars) to harbor life. I shouldn't have to point out that we are ignorant about whether or not life exists on Mars and, if it exists, whether it is widespread enough to be picked up in a surface sample. The Viking results describe a Mars that is very cold most of the time and very dry, but the surface of Mars is neither always cold nor always dry-as recent Mars Global Surveyor pictures have shown. Let me remind readers that not until seven months after Viking 1 landed on Mars did we know about life at deep-sea hydrothermal vents right here on Earth. And Mars is big. We have, literally, only scratched its surface. Mars may indeed be a living planet.

Well, what if it is? Would Mars life necessarily be dangerous?

Hardly. If there is life on Mars, it could be related to life on Earth (due to the natural interchange of materials occasioned by large impact events), or it might be completely unrelated to Earth life. Either scenario would argue for simple prudence in returning a sample from Mars. NASA's current policy, as recommended by the US National Research Council, is not extreme. Rather, it is based on the sound principle that a sample from Mars should be contained until scientists find it does not contain a biohazard.

If Mars life is related to Earth life, then we should find it relatively easy to demonstrate it is not hazardous (if we are lucky enough to bring back anything living in the first place). But readers should be reminded that many Earth organisms, while not coevolved pathogens (for example, ergot fungus, botulism bacteria), are nonetheless dangerous. And Bob should consider his own example (Dutch elm disease) a reminder that organisms, while not human pathogens, can yet cause damage, both environmentally and economically. Still, he insists that Mars life unrelated to Earth organisms couldn't possibly cause harm. How does he know, when we have precisely zero experience with life unrelated to Earth life? Containment and testing are reasonable measures; why not take them? Why shouldn't we avoid the downside? How ought others judge the cost-benefit ratio of Mars exploration if we don't take simple precautions to avoid potentially harmful consequences? Harshly, I suspect.

Due to space limitations, I won't rebut item by item some of Bob's erroneous talking points. And I will agree with him that it would be a terrible loss to sterilize samples prior to their return-it may be difficult to sterilize such samples in any event. One canard to point out, however, is Bob's assertion that "microorganisms are adapted to specific environments," and thus Mars microbes would refrain from living on Earth. This is not a reliable speculation. A notable counterexample from Earth is Deinococcus radiodurans, an organism first isolated from nuclear power plants-environments that did not exist prior to the 1940s. Where did this microbe come from? Deinococcus radiodurans has since been found in natural environments (dry lakebeds) quite unlike Three-Mile Island. What other Earth organisms do we know nothing about?

A rational program of containment and biohazard testing will not only allow us to determine the safety of a returned Mars sample, but it will also allow us the best chance of detecting Mars life, if it exists, when a sample is brought to Earth. Strident arguments on one side ("Mars samples will kill us all!") or the other ("The threat of back contamination is 'hallucinatory'!") do not add value to the discussion about appropriate and reasonable precautions to take in the conduct of what promises to be a vital and intriguing scientific endeavor. The significance of Mars calls for responsible exploration, and Bob Zubrin should have taken more time to inform himself of the real issues at hand. In fact, the time he took to write the piece could have been spent learning enough to have made his opinion much more valuable.

John D. Rummel, Ph.D., is Planetary Protection Officer at NASA Headquarters.