Contamination is one of the greatest risk factors for Mars exploration, but it's not a direct safety risk for a crewed mission. Rather, both flavors of possible contamination are long-term risks to the goals and ideals of the Mars exploration program.
The two possible flavors of contamination are "forward" and "backward". Both will be discussed below.
Forward-contamination is when an Earth microbe hitches a ride along with the crew, escapes into the atmosphere or sub-surface of Mars, and flourishes. Potentially, the Earth-life might replace native Martian life forms or make it impossible for future biologists to tell where Earth-life ends and Mars-life begins. It's the cosmic equivalent of getting your peanut butter mixed up with your chocolate.
Backward-contamination, or simply "back-contamination" as it's usually called, is the same process in reverse. A robust Mars microbe might hitch a ride back to Earth with the Mars team. Once on Earth, the microbe could cause terrestrial diseases or mutate into a green, slimy, fanged space-alien that delights in killing people.
B-movies aside, we Earthlings have never experienced back-contamination in real life, as far as we're aware. However, it's possible to make a half-plausible argument that the universe might be teeming with hostile, primitive organisms that would love to dine at our terrestrial all-you-can-eat salad bar. The reason we've never encountered the problem is because we've never returned anything back to Earth before, oh, except those rocks, equipment, and people from the Moon. The surface of the Moon is an incredibly hostile place for any living organism, so it doesn't count - so reason the back-contamination prophets.
If you believe NASA never sent any Apollo astronauts to the moon, here's a link for you. Also, please read Shadows Of Medusa so you can channel your suspicions in a healthier direction.
Despite the edict of the prophets, the lack of moon-return issues is somewhat damaging to the back-contamination theories. Asteroid impacts have caused chunks of all the inner planets of our solar system to be exchanged (Venus, Earth, the Moon, and Mars are all sneezing on each other). To believe the back-contamination theories, one must envision a swarm of extraterrestrial microbes hearty enough to survive the radiation-scoured surface of Mars, yet fragile enough to die on the Moon. This lessens the odds of our encountering the legendary slimy-green, fanged alien life forms.
Further stacking the deck against them, these microbes will have to survive on the Earth, with its low-radiation, high-pressure, oxidizing environment - truly a hostile place for any Mars-bug. Life forms on Earth are always well adapted to their local environments, though they are sometimes capable of evolving over time if their local conditions change gradually enough. Any stowaway Mars microbe will be in for quite a shock upon reaching Earth... or even upon entering the crewed habitat while it is still on Mars!
With some simple precautions, our crew can minimize the chances of microbe swapping. Any airborne organism will be out of luck because no direct air intakes will happen. The atmosphere of Mars is almost entirely carbon dioxide, a waste gas for our crew. The best chance of finding a Mars-bug will be via water intake. Our Mars crew might drill for water upon their arrival, or they might locate a sub-surface reservoir of ice. Either medium could contain microbes, dormant or active. Since one of the main reasons for finding water on Mars is to drink it, a microbe could easily contaminate the crew... except it would have to get past all those pesky filters designed to prevent just such an event from happening. People on Earth often filter their water, for the same reason. A smart Mars crew will be paranoid about following this simple precaution.
If some hearty microbe does find a way to sneak aboard the habitat, it's only a concern if it's a mostly-benign life form. Any raging killer fungus would be noticed by the crew. Upon detecting a real, native Mars life form, the crew would immediately notify CNN. The brilliant scientific experts in the media would remind the crew that they should study the life form under quarantine conditions. In other words, if any native bug infiltrates the habitat and is noticed, our Mars crew will be in for a looooooong vacation on Mars.
What are we left with? Back-contamination can only happen if some microbe, self-evolved to live on/under Mars (somehow), is able to penetrate the crewed habitat (somehow), stealthily and benignly waiting (somehow) until months or years later when the crew returns to Earth (somehow). After sneaking past the sharp-eyed inspectors in NASA's Planetary Protection Office (somehow), it would have to (somehow) mutate (in a low-radiation environment) into a raging epidemic... and note that epidemics already happen all the time on Earth. For a Mars bug to be any concern at all, it would have to confound the medical community (somehow) by it's very alien nature, yet be able to (somehow) infect and kill compatible (somehow) forms of Earth life. That's one smart Mars-bug!
It would be easy to laugh and make jokes about the "microscopic" chances of all this happening... except it's still possible!! Almost-zero probability is still greater than zero. Therefore, people will still worry about it. Some might even use it as an excuse to halt a crewed Mars mission until we are 100% certain that the crew won't become contaminated by the super-Mars-stealth-bug. Since there will NEVER be any way to guarantee this, crewed Mars exploration will die before it begins (which is the real goal of a small number of frightened bubble-boys out there, of course).
So concludes a brief discussion of back-contamination... almost. One other philosophical point must be mentioned. If we truly live in a universe that is so hostile that a mutant Mars bug can wipe out all life on Earth, then should we let it happen? Is it extreme hubris or cosmic meddling to prevent it? The "let nature take its course" environmentalists are a lot greater in numbers than the "bubble-boys," and a lot louder too. If mankind's destiny is extermination, then what's the difference if we meet our doom from a Mars-fungus, an asteroid impact, a nova, or some self-inflicted cause? Now you know why some philosophers and environmentalists are no fun at parties.
In contrast to the back-contamination theory, which requires an undiscovered Mars-microbe to jumpstart a sequence of events, we know that a Mars crew will bring all sorts of Earth-microbes with them to Mars. This is a real issue, any way you slice it. Fortunately, many of the same safeguards that protect the crew from back-contamination should protect Mars from forward-contamination.
Any Earth microbe that escapes the habitat will need to survive on the surface of Mars, a low-pressure, low-oxygen, high-radiation environment. Few Earthly microbes are believed capable of this feat... though some are a concern. NASA's Planetary Protection Office works both ways, and robotic spacecraft are always sterilized if they are going somewhere that Earth-life could potentially live. Despite the safeguards, Earth-microbes have already contaminated Mars and the Moon on several spacecraft. And don't forget the planetary sneezes, too.
Therefore, worrying about forward-contamination is a bit like closing the barn door after the horse is already out... but we should still try to be good galactic citizens and do the right thing. We still don't know for sure whether any Earth-microbes have survived long enough on the hostile surface of Mars to reach an underground oasis. Also, if any have, we don't know the extent of the contamination. Has Earth-life reached the large underground aquifers that are theorized to exist on Mars? And having reached the aquifers, how far have they spread?
We just don't know. That's one of the rallying cries in favor of exploring Mars, and the forward-contamination issue is no different. We'll have to go there and find out.
When we go there, some will argue that we'll be making the problem much worse. Let's assume our crew doesn't intentionally contaminate the sub-surface aquifers. If a primary goal of our Mars mission is to detect native life forms, which is another safe assumption, then the following outcomes are possible:
That last case is a true cause for concern, for several reasons. Discovery of a compatible Mars-bug would feed into the back-contamination concerns above, so our Mars crew would probably stay on Mars until they knew for sure whether they had found a harmless native bug, a malignant native bug, or an Earth-bug. But what if they can't tell? There's a very real possibility that the results will be inconclusive.
Fortunately, Mars is a big planet. The obvious solution is to send more teams with better equipment and procedures to different places on Mars. If their findings are similar, then the newly-found life forms are a global, almost certainly native, phenomena.
The worst possible scenario (for some people) would be if transplanted Earth-life actually destroys native Mars-life, the truest reversal of the back-contamination argument. This incredibly-unlikely situation might be considered analagous to the settling of the American West, when many natives were killed or relocated. If we're only talking about microbes, which is almost certainly the case, then it's obviously a situation where the benefits to the highest-order life forms (i.e. humans) take precedence over all other reasonable considerations. If you don't believe this, I suggest you avoid using penicillin and anti-bacterial soaps.
In conclusion, we need to push ever-onward while following our safeguards. Let's hope and pray that history won't repeat itself on a microscopic level. That's all anyone can do.
Back to INDEX OF SCIENCE TOPICS
"Perhaps due to her irresolvable issues with Irena, Anna had made a stronger effort to befriend Ollie, superficially at least. Though Ollie acted like a loving uncle toward her, she could never be completely at ease with him. She could never be completely at ease with anyone. Her inner walls were too high and thick. "
Chapter 1