Nick Collins – Telegraph.co.uk August 4, 2011
Scientists are convinced water probably flowed across the surface of the planet at some distant point in history, but have only been able to detect samples of frozen water near the surface.
Should the mysterious streaks prove to be caused by small streams of briny water, they could prove crucial to scientists searching for extraterrestrial life on the planet.
More than 1,000 dark lines were picked up running off steep slopes at some sites in Mars’s southern hemisphere, taken from Nasa’s Reconnaissance Orbiter spacecraft.
They measure between half a metre and five metres in width and stretch up to hundreds of metres in length, and are thought to contain a few litres or tens of litres of water each.
The lines, on slopes facing Mars’s equator, appear to become longer and darker from late spring before fading in the autumn.
In a paper published in the Science journal, researchers from the University of Arizona in the US said that salty water was the “best explanation” for the curious markings.
While the images do not provide proof of the experts’ theory, scientists claim the temperatures on the areas of Mars’s surface would be too warm for frozen carbon dioxide and too cold for pure water.
But salt lowers water’s freezing temperature meaning that despite the coldness of Mars, water as salty as Earth’s oceans could melt in the planet’s warmer season.
Dr Alfred McEwen, who lead the study, said: “The best explanation we have for these observations so far is flow of briny water, although this study does not prove that.
“The problem is if water flows on Mars today it boils, it very rapidly evaporates into the atmosphere and freezes at some depth so unless you catch this right when it is active, and that is a very small area, you wouldn’t expect to see the water.
“In stead it is inference – all the characteristics we see suggest that it is volatile and the temperatures are right for this to be briny water.”
The Nasa orbiter’s imaging equipment, which remotely analyses the chemical make-up of the materials it observes, was unable to confirm the presence of water but this could by because the analysis took place when the water on the surface had dried, Dr McEwen said.
The researchers added that the water may not actually be flowing on the surface, and could instead be buried underneath while still making the ground above it appear dark.
Scientists have been hopeful of discovering water on Mars after identifying fresh-looking gullies on the planet’s surface, but have found no concrete evidence.
Possible droplets of brine have also appeared on the struts of the Phoenix Mars Lander probe which touched down near the Martian north pole in 2008.
Dr McEwen said: “It’s a mystery now, but I think it’s a solvable mystery with further observations and experiments.”