Liquid water runs down canyons and crater walls over the summer months on Mars, according to researchers who say the discovery raises the chances of being home to some form of life.
The trickles leave long, dark stains on the Martian terrain that can reach hundreds of metres downhill in the warmer months, before they dry up in the autumn as surface temperatures drop.
Images taken from the Mars orbit show cliffs, and the steep walls of valleys and craters, streaked with summertime flows that in the most active spots combine to form intricate fan-like patterns.
Scientists are unsure where the water comes from, but it may rise up from underground ice or salty aquifers, or condense out of the thin Martian atmosphere.
“There is liquid water today on the surface of Mars,” Michael Meyer, the lead scientist on Nasa’s Mars exploration programme, told the Guardian. “Because of this, we suspect that it is at least possible to have a habitable environment today.”
Some of the earliest missions to Mars revealed a planet with a watery past. Pictures beamed back to Earth in the 1970s showed a surface crossed by dried-up rivers and plains once submerged beneath vast ancient lakes. Earlier this year, Nasa unveiled evidence of an ocean that might have covered half of the planet’s northern hemisphere in the distant past.
Dark narrow streaks called recurring slope lineae emanate out of the walls of Garni crater on Mars. Photograph: Nasa/AFP/Getty Images
But occasionally, Mars probes have found hints that the planet might still be wet. Nearly a decade ago, Nasa’s Mars Global Surveyor took pictures of what appeared to be water bursting through a gully wall and flowing around boulders and other rocky debris. In 2011, the high-resolution camera on Nasa’s Mars Reconnaissance Orbiter captured what looked like little streams flowing down crater walls from late spring to early autumn. Not wanting to assume too much, mission scientists named the flows “recurring slope lineae” or RSL.
Researchers have now turned to another instrument on board the Mars Reconnaissance Orbiter to analyse the chemistry of the mysterious RSL flows.
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