At the recent Astrobiology Science Conference in Chicago, Dave Beaty and Lindsay Hays of the Jet Propulsion Laboratory asked attendees for their input in narrowing down suitable landing sites for NASA’s Mars 2020 mission. The goal of this JPL-led project is to explore a site likely to have once been habitable, seek signs of past life, then fill a cache with rock and soil samples to be returned later to Earth. The mission will also demonstrate technology needed for future human and robotic Mars exploration. Mars 2020 builds on the expertise gained from the Curiosity rover to search more directly for signs of past microbial life.
Considering these objectives, it is important to have the astrobiology community involved in the mission, including the landing site selection. Choosing a location where microorganisms may have existed in the past or may still exist today will be a big step forward for the project. Unfortunately, due to engineering constraints on the lander (everything from latitude to elevation to the rockiness of the site), we still can’t get to some of the most interesting places on Mars. These include the bottom of Valles Marineris—where liquid water is stable—and the southern highlands of Mars, where life may still be hanging on, extracting water directly from the atmosphere with the help of local salt deposits.
Sadly, it may not make much of a difference. The Mars 2020 mission design appears better suited for demonstrating technology for future robotic and human exploration of Mars (any such progress is very welcome) than to searching for life.
If we learned anything from the 1976 Viking mission and its life detection experiments, it’s that if you put Martian soil in a box for a period of time, any previously measured reactivity, whether chemically or biologically induced, disappears. If a sample cache is returned to Earth after a long time sitting on Mars, there will almost certainly be strict protocols for “planetary protection” to prevent any chance of contaminating Earth with Martian microbes. The returned sample, or at least its container, would have to be thoroughly “baked” before being analyzed by scientists on Earth. The result, I fear, may be that not much valuable information can be gained with respect to life, and perhaps not even with respect to organic compounds that were present in the soil on Mars. Although geologists would get absolute ages from radioactive dating of the returned rocks, biologists would end up getting less straightforward results from a sample return mission.
If we want to search directly for life, more could be accomplished with a series of cheaper missions. A recent round-table discussion of experts agreed that what we really need is a robotic mission with a suite of instruments dedicated to life detection—one that searches for life at or near the Martian surface, rather than bringing Mars rocks back to Earth.