Washington, Oct 29 : NASA's Mars Reconnaissance Orbiter has observed a new category of minerals on Mars, which suggests that the Red Planet may have hosted liquid water on its surface a billion years later than scientists believed, as recently as 2 billion years ago.
Researchers examining data from the orbiter's Compact Reconnaissance Imaging Spectrometer for Mars found the minerals, in the form 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, Maryland.
"The identification of opaline silica tells us that water may have existed as recently as 2 billion years ago," he added.
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.
The newly discovered opaline silicates are the youngest of the three types of hydrated minerals.
They formed where liquid water altered materials created by volcanic activity or meteorite impact on the Martian surface.
One such location noted by scientists is the large Martian canyon system called Valles Marineris.
"We see numerous outcrops of opal-like minerals, commonly in thin layers extending for very long distances around the rim of Valles Marineris and sometimes within the canyon system itself," said Ralph Milliken of NASA's Jet Propulsion Laboratory in Pasadena, California.
The study reveals that the minerals, which also were recently found in Gusev Crater by NASA's Mars rover Spirit, are widespread and occur in relatively young terrains.
In some locations, the orbiter's spectrometer observed opaline silica with iron sulfate minerals, either in or around dry river channels.
This indicates the acidic water remained on the Martian surface for an extended period of time.
Milliken and his colleagues believe that in these areas, low-temperature acidic water was involved in forming the opal.
"What's important is that the longer liquid water existed on Mars, the longer the window during which Mars may have supported life," said Milliken.