Tantalising signs of water activity on Mars
13 Mar 2009
Planetary geologists at Brown University have found a "gully fan system" on Mars that formed about 1.25 million years ago. The fan offers compelling evidence that it was formed by melt water that originated in nearby snow and ice deposits and may stand as the most recent period when water flowed on the planet.
Gullies are known to be young surface features on Mars. But scientists studying the planet have struggled with locating gullies they can conclusively date. In a paper that appears on the cover of the March issue of Geology, the Brown University geologists were able to date the gully system and hypothesise what water was doing there.
The gully system in the Promethei Terra region of Mars appears to have been carved by melt water and may be the most recent period when water was active on the planet.
The gully system shows four intervals where water-borne sediments were carried down the steep slopes of nearby alcoves and deposited in alluvial fans, said Samuel Schon, a Brown graduate student and the paper's lead author.
"You never end up with a pond that you can put goldfish in," Schon said, "but you have transient melt water. You had ice that typically sublimates [goes straight from a solid to a gas]. But in these instances it melted, transported, and deposited sediment in the fan. It didn't last long, but it happened."
The finding comes on the heels of discoveries of water-bearing minerals such as opals and carbonates, the latter of which was announced by Brown graduate student Bethany Ehlmann in a paper in the journal Science in December.
Those discoveries build on evidence that Mars was occasionally wet far longer than many had believed, and that the planet may have hosted a warm, wet environment in some places during its long history.
However, the finding of a gully system, even an isolated one, that supported running water as recently as 1.25 million years ago greatly extends the time that water may have been active on Mars.
It also adds to evidence of a recent ice age on the planet when polar ice is believed to have been transported towards the equator and settled in mid-latitude deposits, said James Head III, professor of geological sciences at Brown, who first approximated the span of the martian ice age in the journal Nature in 2003.
"We think there was recent water on Mars," said Head, who with Brown postdoctoral researcher Caleb Fassett is a contributing author on the paper. "This is a big step in the direction to proving that."
Adapted from information issued by Brown University / NASA / JPL / University of Arizona.
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