From Scientific American:
Although scientists might love to investigate the streaks at close range, strict international rules prohibit Curiosity from touching any part of Mars that could host liquid water, to prevent contamination. But as the rover begins climbing the mountain Aeolis Mons next month, it will probably pass within a few kilometres of a dark streak that grew and shifted between February and July 2012 in ways suggestive of flowing water.
NASA officials are trying to determine whether Earth microbes aboard Curiosity could contaminate the Martian seeps from a distance. If the risk is too high, NASA could shift the rover’s course—but that would present a daunting geographical challenge. There is only one obvious path to the ancient geological formations that Curiosity scientists have been yearning to sample for years.
“We’re very excited to get up to these layers and find the 3-billion-year-old water,” says Ashwin Vasavada, Curiosity’s project scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “Not the ten-day-old water.”
The streaks—dubbed recurring slope lineae (RSLs) because they appear, fade away and reappear seasonally on steep slopes—were first reported on Mars five years ago in a handful of places. The total count is now up to 452 possible RSLs. More than half of those are in the enormous equatorial canyon of Valles Marineris, but they also appear at other latitudes and longitudes. “We’re just finding them all over the place,” says David Stillman, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, who leads the cataloguing.
RSLs typically measure a few metres across and hundreds of metres long. One leading idea is that they form when the chilly Martian surface warms just enough to thaw an ice dam in the soil, allowing water to begin seeping downhill. When temperatures drop, the water freezes and the hillside lightens again until next season. But …