Microbe risk when rover wheels hit martian dirt

Sep 06, 2011 By Jeremy Hsu
The Mars Science Laboratory will be winched down to the martian surface by a sky crane. Credit: NASA/JPL

Earth microbes trying to make it to Mars must survive sterilization 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 study that examined how the new high-tech landing technique of the (MSL) may affect the risk of contaminating Mars. The mission will use both a and downward-firing thruster rockets to slow its descent so that its "sky crane" can lower the SUV-sized 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 Center in Florida. But he added that microbes still face tough odds for surviving and martian conditions.

"Although this paper suggests we could be transferring to martian surface, we don't know for certain yet," Schuerger said. "We could very well be losing most due to the exposure to vacuum in space, 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, 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 in 2004.

A simulated MER wheel illuminated by a UV-enriched light beam within the Mars chamber. Credit: Andrew Schuerger

The Mars Pathfinder rover, called Sojourner, sat on a landing platform for 2 martian days before rolling onto the surface. The twin MER rovers, Spirit and Opportunity, sat on their landing platforms for 12 and 7 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 1, 3 and 6 hours while being exposed to martian levels of ultraviolet (UV) rays. Even such short amounts of time killed between 81 percent and 96.6 percent of the Bacillus subtilis bacteria used in the experiment.

"We did very short UV exposures, and even there we see 96 percent [of bacteria killed] over 6 hours," Schuerger told Astrobiology Magazine. "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 sterilized prior to roll-off than a direct to ground system."

The number of survivors would likely have dropped to practically zero if the experiment had run for 7 or 12 days, Schuerger said.

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 percent of the surface samples ended up showing bacterial growth.

A tray of Mars simulant soil within the Mars chamber during a surface simulation. Credit: Andrew Schuerger

But the contamination level dropped by 50 percent 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.

The second experiment doesn't say anything definitive about the real risk of contamination, Schuerger warned. For instance, it didn't test whether having multiple wheels rolling over the same surface area could bury microbes from the first wheel beneath the . It also didn't simulate the weight of the SUV-sized Curiosity rover that could mash even more microbes into the ground.

On the other hand, the researchers contaminated the rover wheels with perhaps 100,000 times more bacteria compared to what would realistically exist during any of the Mars rover missions. Some Mars rovers get sterilized three or four times, Schuerger said. He added that the journey through space may kill 75 percent of whatever survived after launch.

A test operator in clean-room garb observes rolling of the wheels during the first drive test of NASA's Curiosity rover, on July 23, 2010. Credit: NASA / JPL-Caltech

The next test

What the experiments do suggest is that just having the Curiosity rover sit still for a number of days could help kill off much of the bacteria clinging to its . But the researchers still have questions to answer. "We need to repeat these experiments with much longer time exposures to martian conditions to see if we can get to a rover wheel completely sterilized sitting on a landing pad," Schuerger explained. "We also need to see if 7 or 8 martian days would essentially get to zero amount of survivors, even if we accidentally transferred bacterial spores to the surface."

Such contamination experiments could be done more easily once humans establish a Mars colony and can work alongside their robotic rovers, Schuerger said. But for now, he will have to make do with small Mars simulation chambers on Earth.

The study was detailed in the June 2011 issue of journal Astrobiology.

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User comments : 13

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Jayded
not rated yet Sep 06, 2011
Could someone enlighten me as to why we would go through such lengths to avoid taking microbes to space? I would think we would want them there? Start making life etc
ChiefOfGxBxL
5 / 5 (4) Sep 06, 2011
Could someone enlighten me as to why we would go through such lengths to avoid taking microbes to space? I would think we would want them there? Start making life etc

Well, the Mars rovers are trying to search for proof that life might exist on the planet. If bacteria from the wheels get on the soil and we "discover" it, that could give a false sense of finding life, as it wasn't truly there before. There was actually a similar situation on the moon, where researchers found bacteria on a rock sample collected from the Apollo program, but they dismissed it as it may have come from bacteria on a digging tool that survived the disinfection process.
Free_Thinker
3.7 / 5 (3) Sep 06, 2011
The wheels are not the only parts that will touch the soil - the parachutes and the sky crane platform will, too.
Isaacsname
5 / 5 (2) Sep 06, 2011
Bacillus subtilis is a soil borne microbe, why not use something that is normally exposed to intense UV, like high altitude microbes from the Deinococcus-Thermus class ?
dav36van
2.7 / 5 (7) Sep 06, 2011
Instead of seeding life on another planet, we choose to dig around in the vacant dirt, finding cool geological facts but ultimately returning nothing of biological value to humans and/or nature.

It'd be infinitely more productive to proactively start life there - we'd discover a ton about evolution and adaptivity, possibly even harvest new medicine through it. Real benefits for both nature and mankind.
gmurphy
2.3 / 5 (3) Sep 06, 2011
I'm with dav36van on this one, go forth and multiply!
xznofile
5 / 5 (2) Sep 06, 2011
consider these scenarios: War of the Worlds (HG Wells) where the dominant invaders were defeated by lack of resistance to earth microbes, small carnivores imported to New Zealand, and smallpox on Native Americans and Polynesians. If there's already any life on Mars, it might be good to have a chance to examine it before it becomes extinct. This isn't much of a concern on earth because we have tones of species and destroy a few every day without concern, but it's not a sustainable practice, and we should try to start w/ a clean slate if we visit our neighbors.
xznofile
not rated yet Sep 06, 2011
It's also a chance to develop sterilization techniques so we can be more confident about quarantine when we eventually return from Mars to Earth.
Martian
3 / 5 (2) Sep 06, 2011
Why is there no rover on the moon?
eachus
3.7 / 5 (3) Sep 06, 2011
I remember during the Apollo 11 landing that some daft TV reporter asked Werner von Braun if he thought there was life on the Moon. "Life on the moon? Of course there is life on the Moon! We chust put it there!" ;-)
Sinister1811
1.5 / 5 (8) Sep 07, 2011
I say that if life doesn't exist there already (and, so far, we've found little to no proof that it does), seeding the planet with Earth life wouldn't be such a bad idea. The problem is that it would take millions of years for simple organisms to gradually become more complex organisms.

Also, I like the thought of eventually terraforming Mars. I hope we'll be able to do that in the future.
CHollman82
2.1 / 5 (7) Sep 07, 2011
Instead of seeding life on another planet, we choose to dig around in the vacant dirt, finding cool geological facts but ultimately returning nothing of biological value to humans and/or nature.

It'd be infinitely more productive to proactively start life there - we'd discover a ton about evolution and adaptivity, possibly even harvest new medicine through it. Real benefits for both nature and mankind.


This is dumb... Assuming any form of Earthly life can even survive long term on Mars it would take hundreds of millions of years before evolution produced anything of interest to us today, and by that point I would hope the experiment would be considered as relevant as Newtons falling apple.
Sinister1811
1 / 5 (4) Sep 12, 2011
@Ojorf - What was wrong with my post about Terraforming Mars? I was basically saying that any simplistic life form would take millions of years to become anything complex. Is there something wrong with that? And at this stage, there is no reason to believe that there IS life on Mars. Unless you have some proof that you could provide me with? Thanks for the 1 rating, cretin.