“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 reported1 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.