A test operator in clean-room garb observes rolling of the wheels during the first drive test of NASA's Curiosity rover.
Credit: NASA / JPL-Caltech
MARYLAND: Mars's surface is at risk of contamination by Earth microbes, according to a new report on NASA's Mars Science Laboratory rover.
Earth microbes trying to make it to Mars must survive sterilisation in NASA's clean rooms, harsh cosmic rays during months of space travel and the Red Planet's unforgiving surface environment. But any bacteria that successfully hitchhike aboard the wheels of NASA's Mars Science Laboratory mission in 2012 might manage to scratch out a brief existence on the Martian surface.
The finding comes from a recent study published in the journal Astrobiology that examined how the new high-tech landing technique of the Mars Science Laboratory (MSL) may affect the risk of contaminating Mars. The mission will use both a parachute and downward-firing thruster rockets to slow its descent so that its 'sky crane' can lower the SUV-sized Curiosity rover onto the surface - a direct touchdown that may give microbes a brief chance to experience life on Mars.
That translates into a higher risk of contamination when compared to some past Mars rover missions, said Andrew C. Schuerger, a microbiologist at the University of Florida and the Space Life Sciences Lab at NASA's Kennedy Space Centre in Florida. But he added that microbes still face tough odds for surviving space travel and Martian conditions.
"Although this paper suggests we could be transferring bacteria to Martian surface, we don't know for certain yet," he said. "We could very well be losing most due to the exposure to vacuum in space, cosmic rays and hard radiation. Even if cells are present on a rover wheel at launch, they might be dead by the time they get to Mars."
Standing still
Schuerger and his colleague, Krystal Kerney, also from the University of Florida, wanted to find out whether the wheels of Mars rovers past and future could contaminate the Martian surface. They ran two experiments simulating the contamination possibilities for MSL versus the Mars Pathfinder mission of 1997 and the Mars Exploration Rovers (MER) that landed on the red planet in 2004.
The Mars Pathfinder rover, called Sojourner, sat on a landing platform for two Martian days before rolling onto the surface. The twin MER rovers, Spirit and Opportunity, sat on their landing platforms for 12 and seven Martian days, respectively. Each Martian day is just a little over 24 hours.
In the recent study, researchers simulated a Mars rover sitting on a landing platform for one, three and six hours while being exposed to Martian levels of ultraviolet (UV) rays. Even such short amounts of time killed between 81% and 96.6%of the Bacillus subtilis bacteria used in the experiment.
"We did very short UV exposures, and even there we see 96% [of bacteria killed] over six hours," Schuerger said. "That's a very dramatic and a very positive sign that a rover wheel which sits on a platform, like MER did, has a much better chance of being sterilised prior to roll-off than a direct to ground system." He added that the number of survivors would likely have dropped to practically zero if the experiment had run for seven or 12 days.
Rolling in the dirt
By contrast, the second experiment simulated how a rover wheel in the future MSL mission would immediately come into contact with the Martian surface. When the contaminated rover wheel rolled over the simulated surface, about 31.7% of the surface samples ended up showing bacterial growth.
But the contamination level dropped by 50% after 24 hours of exposure to simulated Mars conditions, such as UV radiation, low pressure, low temperature and high levels of carbon dioxide. The results pointed once again to the harshness of the Martian surface environment for Earth life.
