EVIDENCE that has raised hopes that the planet may support life. But those hopes mean different things to different people.
Astrobiologists see the findings as confirmation that Mars is the best hope in our solar system to host Earth-like life 鈥� so they want to keep it pristine as they search. But advocates of crewed space flight see water as a , a vital for a visit by astronauts.
Missions to the surface of Mars must abide by designed to avoid contaminating 鈥渟pecial regions鈥� that might sustain life. Anywhere with permanent or temporary liquid water falls into that definition 鈥� the very places we want to check.
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For the astrobiologists, sterilising robots for exploration can in principle reduce the contamination risk. But this is very difficult, and a further barrier remains: everything we have learned so far suggests that it won鈥檛 be easy to detect life on Mars, and robots are inherently limited in what they can do.
Humans would be better able to look for evidence of life. NASA鈥檚 science chief has said as much, and the agency is busily talking up its ambition to get people there in the 2030s.
But a panel of the US National Academy of Sciences that fully following planetary protection rules 鈥渕ay prevent humans from landing in or entering鈥� special regions on Mars, because we carry microbes that could survive there.
It is a dilemma. Perhaps the best approach would be to start with an option that lies between the two camps. Robotic sample-return missions are no guarantee of a definitive answer to the life question, but analysis on Earth would be more detailed and powerful than is possible remotely.
鈥淪ample-return missions would allow more detailed and powerful analysis on Earth鈥�
NASA has long proposed a mission to bring back rocks. No date is set, but its latest timetable calls for the Mars 2020 rover to stash samples. A return mission needs to become a top priority, with possible follow-ons depending on what is found.
Given the , trying to answer the life question before landing there is sensible. If that鈥檚 not possible, the question will shape the agenda for the first visitors.
This article appeared in print under the headline 鈥淢artians first鈥�
