It's important for a surgeon to disinfect his/her hands (and lower arms) before going elbows-deep into a patient's chest. This makes sense; bacteria is everywhere and the last thing you want is some pesky E. coli setting up colonies around coronary arteries.
This is also true for missions to Mars; stringent anti-bacterial measures are taken to make sure every surface mission is as clean as possible. This avoids spoiling the pristine Martian environment; it minimizes the risk of contaminating experimental results; it also reduces the risk creating a species of super-charged terrestrial bacterial setting up home on the Red Planet, waiting to infect future human settlers "Andromeda Strain"-style (however, these bugs wont be alien in origin, they'll be the evolved nightmarish cousins of bacteria you'd normally find in boogers).
But wait. Scientists have aired concern that protecting Mars from our germs is actually hindering exploration of the Red Planet. Why? Well, keeping clean can be costly and, besides, we've probably already done an interplanetary sneeze into Mars' orbit anyway. Dirty, dirty Earth PHOTOS: Mars Through Curiosity's Powerful MAHLI Camera
In a study published in the journal Nature Geoscience, astrobiologists Alberto Fairén of Cornell University and Dirk Schulze-Makuch of Washington State University claim "the protocols and policies of Planetary Protection are unnecessarily restricting Mars exploration and need to be revised." The sheer expense of trying to completely sanitize surface missions of Terrestrial microbial life, they argue, is making missions searching for Martian microbial life "unviable."
NASA's Office of Planetary Protection was set up to make sure that all life remains on Earth. So, to make sure we don't accidentally invade Mars with a wave of microbial colonists, NASA (and other space agencies) go through great pains and expense to make sure every component is as microbe-free as possible before launch.
Interestingly, the issue of planetary protection was thrown into the limelight in December 2011 when it became known that one of the components attached to NASA's Mars Science Laboratory did not adhere to strict Planetary Protection rules. A set of drill bits did not go through the final ultra-cleanliness step before they were attached to the rover for launch. This mishap was made public days after Curiosity was launched and Earth was in the spacecraft's rearview mirror. Oops.
Also, analysis suggests that no matter how much sterilization of Curiosity was carried out, some hardy Earth-based bacteria may still have hitched a ride in the tread of the rover's wheels. It's exactly this kind of hardy microbe that shouldn't be sent to Mars. Double oops.
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But what does it take to become a successful Mars-bound bacterial stowaway anyway?
In 2010, University of Central Florida researchers tortured several different species of microbe to see which was made of the "Right Stuff." Microbes including acinetobacter, bacillus, escherichia, staphylococcus and streptococcus were exposed to the freezing, radioactive environment of a Mars environment analog. The results were, well, rather unsanitary. Though none of the species of bacteria really enjoyed their Martian vacations, Escherichia coli camped out and survived the ordeal (although it didn't feel like reproducing very much). A strain of E. coli is most famous for causing food poisoning.
Other, more recent studies have also been carried out and their results are suggestive that a very small number of bacteria may be able to eke out a microbial living in the Martian regolith.
But all of this is OK, according to Fairén and Schulze-Makuch. If these microbes can survive the harsh Mars environment, Earth has probably already infected the planet.
We know that meteorites from Mars have landed on Earth and, logically, meteorites have carried material from Earth to Mars. Energetic asteroid impacts on the solar system's planets' surfaces share material throughout interplanetary space. If a chunk of Earth material were to be blasted into space by a big meteorite impact, any bacteria inside could survive inside their rocky spaceship and crash-land into the Martian crust. Should they survive the voyage, they could already be on Mars, having been deposited there millions of years ago.
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This planetary microbe sharing is known as panspermia, but it is pure conjecture for now as there is no evidence that anything living has been transferred between the planets - although some Earth-based life has shown a certain flair for surviving for long periods in space, so the mechanism at least seems possible.
Although Fairén and Schulze-Makuch's objections to planetary protection seem logical, their motivation is primarily financial. "As planetary exploration faces drastic budget cuts globally, it is critical to avoid unnecessary expenses and reroute the limited taxpayers' money to missions that can have the greatest impact on planetary exploration," they add.
It may be expensive to sanitize missions before landing on any planetary body, but we have little clue about the impacts of accidentally infecting an alien landscape with Earth microbes. Yes, the panspermia mechanism may have already spread Earth life far and wide. And yes, hardy bacteria may have already stowed away on missions (no matter how well they've been cleaned). But not carrying out these cleaning procedures, increasing the risk of cross-planetary contamination, in an effort to cut costs seems a little reckless at this early stage in our understanding about the potential genesis of life on other worlds.
But still, it would be rather exciting to find biology on Mars with a distinctive Earth Brand™ life flavor - that would at least add some experimental evidence in the favor of panspermia, expanding the possibilities for life beyond terrestrial soil.
Image: Dirty wheels? Curiosity snaps a photo of its wheels using its robotic arm-mounted MAHLI camera. Credit: NASA/JPL-Caltech