Nov. 9, 2006 — A Martian mineral touted as proof of past lakes on the Red Planet may be the result of a rather dry acidic fog instead, say geologists.
When the sulfur-rich mineral jarosite was found in layered rocks of an area known as Meridiani Planum by a Mars Exploration Rover, NASA experts were quick to say it was evidence there was once a shallow lake there, which left the mineral as a salt crust when it evaporated.
But new research into how jarosite coatings form on Earth rocks at the summit of the Kilauea volcano in Hawaii points to a much drier origin.
Noxious sulfur dioxide gas is constantly spewing from Kilauea's Halemaumau crater, report University of California at Davis geologist Peter Schiffman and his colleagues in the November issue of the journal Geology. The gas sticks to the ground downwind of the crater in the Kau Desert as a sulfuric acid fog.
There the volcanic rocks are coated with a thin mineral layer that includes jarosite.
Schiffman and his team simulated the unusual chemical circumstances of the Kau Desert rocks and found that the jarosite probably forms when the volcanic acid fog soaks the surfaces of the rocks, then evaporates away, leaving behind volcanic minerals that react with the sulfuric acid and create the jarosite coating.
The jarosite is just one piece of evidence among many that scientists use to build the case that Mars was once a wet planet, but it was held up by many as the most conclusive to date. Schiffman's work calls that conclusion into question.
"While there is an increasing amount of evidence that suggests the existence of liquid water on the surface of Mars at some time in the past," reported Schiffman, "there is no a priori reason that standing bodies of liquid water must have existed at the time of jarosite formation."
