Original URL: http://www.theregister.co.uk/2008/10/29/mars_opal_discovery/

NASA probe finds opals in Martian crevices

Mars became Australian uninhabitable later than thought

By Lewis Page

Posted in Science, 29th October 2008 11:03 GMT

A NASA space probe orbiting Mars has discovered deposits of opals in the mighty Valles Marineris canyon system* east of Tharsis. Opals aren't valuable enough to justify interplanetary trade, but the discovery is significant as it suggests that liquid water existed on Mars a billion years more recently than had been thought.

NASA orbital pic showing the Martian opal deposits

The opal mines of the Valles Marineris.

"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 of Johns Hopkins University, in charge of the Mars Reconnaissance Orbiter's spectrometer scope.

"The identification of opaline silica tells us that water may have existed as recently as 2 billion years ago."

Until lately, Mars boffins had reckoned that the last liquid water disappeared from the Red Planet's surface at least three billion years ago. This was based on discoveries of "clay-like" phyllosilicates and hydrated sulphates. But the new opal finds have caused NASA to revise the date of the Great Drying forward by a billion years.

"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. Milliken is one of NASA's top Martian water-formed gemstone brains, seemingly.

The new interplanetary gemstone discoveries make intuitive sense, at any rate. Most of Earth's opals come from Australia, a region which like Mars is remote, dry and predominantly red. The opal is in fact Australia's national gemstone. ®

*The "largest known crevice in the solar system", apparently.