The best explanation they have so far is that those dark, fingerlike streaks are a kind of salty water that is running on or just below the Martian surface. At one location — Newton Crater — they have counted as many as 1,000 of these possible streams flowing down the slopes and into a basin.
It’s a discovery that, if confirmed, would fundamentally change the understanding of Mars and would strongly support the widely held theory that the planet was once far more wet and warm. And scientists say the discovery of water would provide the best target yet for finding possible life beyond Earth.
“We haven’t found any good way to explain what we’re seeing without water,” said Alfred McEwan of the University of Arizona’s Lunar and Planetary Laboratory. McEwan is the lead author on a paper about the discovery in the journal Science.
“And if we confirm that it is a salty water, then we have the best idea yet about where to go to try to find extant life on Mars,” McEwan said.
The dark streaks were initially noticed by a student at the school in images sent back by the Mars Reconnaissance Orbiter (MRO). The pixelated images were taken as far back as 2007, but with so much data coming in from space missions, they had remained unstudied. McEwan suggested that the student — geophysics junior Lujendra Ojha — examine over time the locations with streaks, and Ojha found that the streaks changed dramatically by season.
“None of these images by themselves are particularly revealing,” McEwan said. “But when you put them together and see what happens over time, then you can clearly see something important is happening.”
Gradually, a team of researchers determined that the changes came with increasing and decreasing temperatures. They began scouring the MRO images for other similar sequences and so far have found seven confirmed locations and possibly 32 more. In all cases, the flows appear to go around, rather than over, obstacles such as rocks, and sometimes they peter out before they reach flat ground. They are generally between about two feet and 15 feet wide, and occur during the Martian summer, when temperatures range from 10 degrees below zero to 80 degrees Fahrenheit.
At a NASA news conference Thursday, McEwan and others associated with the MRO, Mars science and astrobiology hailed the finding as a potential turning point. Philip R. Christensen, a geophysicist at Arizona State University, said it constituted the best evidence for the possible existence of water on the Martian surface. Indiana University biogeochemist and astrobiologist Lisa Pratt said it also offered the most promising habitat discovered for current Martian life and speculated that the conditions could be similar to Siberian permafrost, where life exists. All of the speakers, however, said the finding was, at this point, circumstantial rather than proven.