Year in review: Best evidence yet for water on Mars

There’s water on Mars. Yes, again.

In the most highly publicized Mars discovery of the year, NASA announced that its Mars Reconnaissance Orbiter spacecraft had spotted hydrated salt minerals on the Red Planet (SN: 10/31/15, p. 17). The salty streaks appear in the same places as dark, hillside marks that lengthen and shrink with the Martian seasons. Brine probably oozes from the steep slopes, scientists concluded.

Water on Mars has been reported many times in the past, with each discovery adding fresh nuance to scientists’ picture of the planet. The brine finding is the most detailed evidence yet that water flows on the planet’s surface today. And liquid water — no matter the saltiness — has exciting implications for whether life could exist on Mars.

Chemical evidence for Martian habitability, both past and present, is piling up elsewhere as well. The Curiosity rover, which has been rolling across the planet since 2012, identified a form of nitrogen in Martian rocks that, on Earth, is used to construct biological molecules (SN Online: 3/23/15). Studies of six Martian meteorites, blasted into space by asteroid impacts, reveal that they contain methane, which serves as a food source for microbes on Earth (SN Online: 6/16/15).

Knowing whether there really is life on Mars — or ever was — will have to wait until at least 2020, when NASA plans to launch a rover to collect and store rocks that would eventually be flown back to Earth for analysis. In the meantime, scientists’ freshest views of Mars are from the sky. The MAVEN spacecraft, flying high through the Martian air, has spotted glowing auroras and puzzling dust clouds (SN: 4/18/15, p. 15). And it has measured, more precisely than ever, how powerful solar storms eroded away Mars’ atmosphere (SN: 12/12/15, p. 32), a process that, over billions of years, has caused the Red Planet to lose most of its air.