Genome sequencers and other devices that could reveal whether anything is alive on Mars right now should be ready to launch with NASA's next Mars rover in 2020. The trouble is, the rover team may not want them ? and some astrobiologists are crying foul.
Earlier this week NASA announced its science goals for the next US rover headed for the Red Planet, known for now as Mars 2020. Essentially a duplicate of the Curiosity rover now on Mars, this robot has been tasked with searching for evidence of past life and collecting rock samples for eventual return to Earth. Sample-return has been at the top of the Mars community's wish list for decades. The caching component of Mars 2020 represents a revival of a well-studied plan to bring Martian rocks back to Earth for detailed study.
But others think the rover's approach to life detection is overly cautious. The Mars 2020 will primarily search for signs that something lived on Mars in ancient times, even though the technology exists to hunt for alien microbes presently living on or just beneath the surface.
"It is the same old depressing story of NASA vetoing any proposal to do biological experiments on Mars," says Paul Davies of Arizona State University (ASU) in Tempe. "I personally think this is absurd."
Martian genes
One potential life-seeking experiment is the Search for Extraterrestrial Genomes (SETG) project, based at the Massachusetts Institute of Technology. Previous experiments for detecting existing life on Mars, such as the one on the 1976 Viking missions, focused on finding organic carbon, which is necessary for life as we know it but can also be produced by non-biological processes. Viking scientists initially reported such hints of life on Mars, but the results were ultimately deemed inconclusive.
"We went and looked for life on Mars with Viking, and since then we've been in the mode of looking for past life," says Chris Carr of the SETG project. "That's made sense. We didn't want to repeat Viking, where we couldn't make sense of the results."
Finding DNA or RNA would be a much less ambiguous signal of life, past or present. A gene sequencer could even figure out whether that life is related to Earth life, or if it had a unique origin. Doing DNA analysis on Mars rather than waiting for the Mars 2020 samples to come home also means you can be confident that the samples have not degraded in transit.
"Sample-return is an important mission and we should do it, but I don't think we should wait until we have all parts of that mission to look for extant life on Mars," says Carr. His team is developing a robust sequencer small enough to fit on a rover, and they are already field-testing prototypes. "I think we could produce something in time for the Mars 2020 mission," he says.
Encourage life
An even simpler experiment would create habitable hot spots on Mars. Dirk Schulze-Makuch of Washington State University and colleagues argue that if microbes are currently present on Mars, they may be lying dormant to survive the planet's extreme dryness and cold. If you could warm them up, protect them from radiation and give them a refreshing drink, they might bloom.
Their project, outlined in a paper published this week in the journal Astrobiology, is called Detection of Mars Extant life in the near-Subsurface (DOMES). A rover would scratch out a trench to expose the Martian subsurface and put down a clear plastic cup containing water and organic compounds, inverted like a tiny biodome. Similar schemes have encouraged lichen and moss to flourish in the otherwise sparsely populated sands of the Namib Desert.
Gil Levin of ASU, who led Viking's life-detection efforts, still hopes to see that experiment vindicated. "NASA says the greatest question confronting us is, are we alone?" says Levin. "Thirty-seven years ago, they got at least an ambiguous response. What do you do with an ambiguous response? You settle it. You don't run away from it."
Together with Davies and Ariel Anbar, also of ASU, Levin is currently developing a capsule that would carry multiple small, dart-like instruments, which could shoot away from a rover or lander, plunge down into the soil and repeat the Viking experiment several times with different controls. "That would not only verify that we had detected life previously or disprove it, but would also begin an investigation of what kind of life that is," he says.
Mars rocks
NASA is throwing open the door for proposed instruments to fly on Mars 2020, so while these experiments may go beyond the rover's stated goal, they can still compete for a spot. And if they are not selected for this launch, the sample-return effort may give them another shot.
The most likely strategy for returning samples stored on the 2020 rover will involve two more spacecraft heading to Mars, says Charles Whetsel of NASA's Jet Propulsion Laboratory in Pasadena, California. Another rover will need to pick up the cache and loft it into orbit, and an orbiter or flyby mission will have to pick it up. Both of those missions would offer opportunities for new science experiments that could search for extant life, either carried on the pickup rover or dropped by the orbiter.
In the meantime, Whetsel defends the decision to hold off on searching for existing life right now. "It's probably easier to prove there was once life on Mars than to prove it survived and it exists today," he says. "It would definitely be front-page news if we determined there is currently life on Mars. I think it's equally front-page to say there was once life on Mars."
Journal reference: Astrobiology, DOI: 10.1089/ast.2013.0995
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