Opals on Mars Reveal Planet's Long Wet Past

Oct. 29, 2008 -- Opals have long been prized for their luster and beauty but the discovery that they also exist on Mars is proving to be gem of another variety.

The deposits, spotted from orbit by a NASA probe, indicate Mars may have been wet for a billion years longer than previously thought. If true, that could have significant impacts for whether the planet was suitable to host life.

"Water may have existed as recently as two billion years ago," said John Hopkins University's Scott Murchie, a lead scientist with the Mars Reconnaissance Orbiter team. "It extends the time range for liquid water on Mars, and the places where it might have supported life."

The finding of a new category of hydrated minerals on Mars was reported in the November issue of Geology.

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The silica-based deposits are the third -- and most significantly, the youngest -- type of water-containing mineral discovered on Mars.

The oldest hydrated materials are clay-like phyllosilicates, which formed more than 3.5 billion years ago when volcanic rocks bathed for long periods of time in water.

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Later, hydrated sulfates formed when salty and occasionally acidic water evaporated.

Hydrated silicates, commonly known as opals, formed when liquid water altered materials created by volcanic activity or meteorite impacts on the planet's surface. They have been found in Gusev Crater by the rover Spirit and by MRO in the Valles Marineris canyons and other relatively young areas of Mars.

"We see numerous outcrops of opal-like minerals … around the rim of Valles Marineris and sometimes within the canyon system itself," said Ralph Milliken with NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Some of the hydrated silica deposits spotted by MRO were mixed with iron sulfates, which formed when long-standing acidic water evaporated. Milliken and his colleagues think the water played a role in the formation of the opals.