Since the Mars rover Curiosity landed near Mount Sharp in 2012, features that might be caused by seasonal flows of water have been spotted on the peak鈥檚 slopes. Should we send Curiosity to take a closer look? .
If temporary liquid water is present, it would make these places so-called 鈥渟pecial regions鈥�, which enjoy a higher status under planetary-protection guidelines. Only rovers and landers that have been rigorously sterilised, unlike Curiosity, are supposed to examine them, to avoid possible contamination from microbes that hitched a ride from Earth.
But does maintaining this rule make sense? NASA plans a series of human missions to Mars in the 2030s, which makes contamination ever more likely anyway. And those missions will , so shouldn鈥檛 we do all we can to find out what the first astronauts will encounter in such places?
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In any case, we must recognise that Mars has already been contaminated, both from non- or poorly sterilised spacecraft and the earlier interplanetary transfer of life through rocks ejected from Earth during asteroid impacts that later landed on Mars.
The latter must have occurred many times on a much warmer and wetter Mars in the early history of the solar system. If so, life that came from Earth might be widespread there. Even if life on Mars originated independently, it would have been exposed to terrestrial cousins long ago.
Like parrots in Antarctica
Any talk of Earth-based microbes carried by spacecraft as an invasive species likely to displace Martian life is like imagining penguins in the Antarctic being usurped by parrots from the jungle. The Martian environment is extreme and sterilising at the surface, and new arrivals would be pounded by radiation and exposed to huge聽temperature swings, reactive minerals and nasty chemicals. Survival is not impossible, but the chances are remote.
Our current best sterilisation methods for spacecraft are prohibitively costly, and not 100 per cent effective 鈥� so Earth鈥檚 toughest microbes can still make the journey to Mars anyway. In effect, the rules mean that no spacecraft is likely to go any time soon to a place on Mars where life could exist.
Planetary protection is, of course, extremely important, but the emphasis should be on protecting our own planet. Searching for life on Mars is safer than bringing samples back to Earth, risking contamination of our planet.
Critics of any talk of changing the rules will argue that we risk mistaking a terrestrial hitch-hiker for a Martian. However, that risk is tiny.
If there is life on Mars, the most likely scenario is that it originated independently or experienced a long evolutionary time span after being relocated from Earth 鈥� in which case we would be able to identify the biochemical differences to tell it apart.
If not, or if life on Mars just happened to evolve to be so biochemically similar to Earth鈥檚 that it is difficult to distinguish in this way, then we would be able to sequence its DNA and place it on the genetic tree of life.
Current planetary protection policy is too restrictive. It is not allowing us to go to places that are interesting and where we might find life. We should change it and let Curiosity take this chance to examine what could be seasonal water flows.
