SCIENTISTS may have found opals on Mars.
While possibly not worth mining, the discovery suggests the planet had been awash with water for billions of years, potentially long enough for life to form.
NASA scientists announced yesterday that their Mars Reconnaissance Orbiter, which has circled the planet since 2006, had spotted hydrated silica, or opal – which only forms in water – "spread across large regions", including a massive canyon named 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.
Another mission scientist, Dr Scott Murchie, from Maryland’s Johns Hopkins University, said "the identification of opaline silica tells us that water may have existed as recently as 2 billion years ago".
An earlier discovery of clay-like minerals indicated the planet was wet more than 3.5 billion years ago.
"What’s important," said Dr Milliken, "is that the longer liquid water existed on Mars, the longer the window during which Mars may have supported life."
It was further revealed yesterday that opaline silica had also been found by Spirit, one of two NASA rovers that landed on Mars in 2004.
Marion Anderson, a Monash University geologist who helped select the rover landing sites, said finding opaline silica "means that water was around for at least a billion years longer than previously thought".
Ms Anderson warned that Martian opals were not necessarily valuable as gems. "You must remember that on Earth, the vast majority of opal is not precious opal. If the water molecules are in the right place, incoming light is refracted to give you the colour play known as opalescence.
"Opal which is not precious … is commonly known as potch, and is of no commercial value.
"What the presence of opaline silicates on Mars does tell you is that the silicate that contains the water formed in places where there were high levels of free water within the rocks while the silicate was precipitating out. This is significant, as it again proves that Mars has had a wet history."