There are certain areas on Mars where we donāt dare tread. NASA forbids spacecraft from visiting spots that possibly host liquid water where life might be able to thrive, for fear of contaminating Mars with Earth microbes. But an analysis of the salty liquids on Mars suggests we neednāt worry, because life as we know it would be unable toĀ exist anywhere on the Martian surface.
Edgard Rivera-ValentĆn at the Lunar and Planetary Institute in Texas and his colleagues used maps of the temperature and relative humidity across Mars to map the presence of salty water ā any water on the Martian surface is likely to be salty, simply because the surface itself is. ThisĀ improves the chances of water being liquid, because salt lowers the freezing point of water.
āYou can think about it as if you throw salt on ice on the sidewalk,ā says Danielle Nuding at NASAās Jet Propulsion Laboratory in California. āItās the same chemistry happening.ā
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Unfortunately, the saltier the water, the less likely anything can survive it. The researchers found that even though there could be briny water on the surface of Mars up to 18 per cent of the year depending on the season, no microbe we have ever seen on Earth would be able to reproduce there.
āLife as we know it is not going to find these brines and survive, because itās either going to be way too cold or way too salty,ā says Rivera-ValentĆn, who presented the results on 18 March at the Lunar and Planetary Science Conference in Texas.
That doesnāt mean we canāt contaminate Mars: brines with different types of salts mixed together might be friendlier to life, and temperatures just below the surface are much less extreme.
Nevertheless, as long as we donāt dig down, it might be impossible or at least highly unlikely for rovers to contaminate Mars. āThe level of sterilisation that weāve done with Curiosity should be good enough to ignore what weāve been calling āspecial regionsā until now,ā says Jennifer Hanley at Lowell Observatory in Arizona. āI think that weāre OK to go.ā
Visiting these regions would be particularly helpful because, while they are in theory the most vulnerable areas on Mars, they are also the most interesting. For example, arguments have been raging for over a decade about whether dark streaks on Martian slopes called recurring slope lineae are flowing water or just dust. A quick visit by the Curiosity rover, which is near an area where these flows often form, could solve it once and for all.
Even if these wet areas arenāt hospitable to Earth life, they could still be home to native Martian life forms. āIf you had life that originated on Mars when it was more habitable, it could be that as Mars changed life could have gradually adapted to the new, more extreme conditions,ā says Rivera-ValentĆn.
