Image credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University. Epsilon Eridani might be too young, and too cool.. but there’s always wondrous Mars.. NASA are slowing turning off Phoenix in an effort to conserve power. But its already spotted water-ice clouds [and snow! – Ed] and they’ve tasted the water there. But the evidence of vast lakes, flowing rivers and deltas on early Mars, from about 4.6 billion years ago to 3.8 billion years ago, has come from the Mars Reconnaissance Orbiter. Now the Orbiter has spotted “a hydrated mineral similar to opal” which “tells us that [surface] water may have existed as recently as 2 billion years ago.”
“What’s important is that the longer liquid water existed on Mars, the longer the window during which Mars may have supported life,” says [Ralph Milliken of NASA’s Jet Propulsion Laboratory in Pasadena, Calif]. “The opaline silica deposits would be good places to explore to assess the potential for habitability on Mars, especially in these younger terrains.”
From the JPL press release
Researchers examining data from the orbiter’s Compact Reconnaissance Imaging Spectrometer for Mars have found evidence of hydrated silica, commonly known as opal. The hydrated, or water-containing, mineral deposits are telltale signs of where and when water was present on ancient Mars.
“This is an exciting discovery because it extends the time range for liquid water on Mars, and the places where it might have supported life,” said Scott Murchie, the spectrometer’s principal investigator at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. “The identification of opaline silica tells us that water may have existed as recently as 2 billion years ago.”
Until now, only two major groups of hydrated minerals, phyllosilicates and hydrated sulfates, had been observed by spacecraft orbiting Mars. Clay-like phyllosilicates formed more than 3.5 billion years ago where igneous rock came into long-term contact with water. During the next several hundred million years, until approximately 3 billion years ago, hydrated sulfates formed from the evaporation of salty and sometimes acidic water.
And from the Nasa image text
The opal minerals are located in distinct beds of rock outside of the large Valles Marineris canyon system and are also found in rocks within the canyon. The presence of opal in these relatively young rocks tells scientists that water, possibly as rivers and small ponds, interacted with the surface as recently as two billion years ago, one billion years later than scientists had expected. The discovery of this new category of minerals spread across large regions of Mars suggests that liquid water played an important role in shaping the planet’s surface and possibly hosting life.