Dark streaks on the sides of Martian craters. Possibly water. Streams that flow only in the planet’s summer. Possibly. And life? All we can say for certain is not that there is, or was, life on the Red Planet, but that if it did /does exist we can now understand how it came about and developed. The essential building blocks are there. And water, or at least brine, almost certainly.
A paper just published in Nature Geoscience by Lujendra Ojha of the Georgia Institute of Technology has caused considerable scientific excitement with its remote study both of the changing shape and colour of these streaks – what she calls "recurrent slope lineae" (RSLs) – and of the spectroscopic analysis of their chemical composition. The salts found, compounds that need water to form, have excellent antifreeze properties capable of lowering the melting point of water by some 70C, sufficient to thaw icy water on Mars's inhospitable surface during summer months. "We're not claiming that we found . . . evidence of liquid water. We found hydrated salts," Ms Ojha says.
But the news that Mars is almost certainly wet and a dynamic, seasonally changing environment raises the intriguing possibility that the planet, until now seen as largely arid, can support life in some form. How deep under the surface, and how salty, the water might be remain important and significant unknowns, and identifying remotely any bacteria present is technically very difficult.
The presence of water if confirmed will also make significantly easier the prospect of supporting humans during future exploration. But that’s still some way off. Curiosity, a car-sized rover has been trundling over the surface since 2012, while NASA is planning a follow-up unmanned mission, which should arrive in 2020. It is developing the capabilities needed to send humans to an asteroid by 2025 and Mars in the 2030s. A joint report from the National Academy of Sciences and the European Science Foundation also recently warned of the ethical challenge involved in sending a manned flight to Mars which might irretrievably contaminate any native bacteria.