"Many times in craters or places where you'd expect to find lake beds, the [evidence] would be buried by things that happened later over three or four billion years of geological activity," Grant said.
"[At Holden Crater] an unusual episode, a high-energy flood event, may have exposed some of these lake beds."
According to Grant's theory, the first lake inside the crater dried up, and later the plateau around the crater became inundated with water from Uzboi Vallis, a natural canal system.
The crater's rim eventually gave way to a torrential flood that shredded large blocks of sediment to expose the deeper lakebeds and megabeccia.
(Related news: "River-Size 'Flash Floods' May Have Carved Mars Craters" [February 20, 2008].) Grant and colleagues will present their research in an upcoming issue of the journal Geology.
Liquid Debate
But some experts, including University of Arizona astrophysicist Ethan Siegel, remain lukewarm on theories of a wet Mars.
"The geophysical community pretty much accepts that there was water on Mars, but where, when, and how much are open for debate," Siegel said.
"There is some evidence that there was water, like the meanders of what look like streambeds, and some evidence that there wasn't water, like the lack of carbonate deposits in those so-called streambeds."
On Earth carbonate minerals require liquid water to form, so their presence on the red planet would be the proverbial "squirting gun."
If the clay sediments in Holden Crater are found to contain carbonates, "that, indeed, may go a long way toward providing more evidence for a wet past on Mars," Siegel said.
Future missions, like the Martian Science Laboratory slated for launch in September 2009, could lay the matter to rest.
The lab's rovers are due to arrive on Mars in 2010, and Holden Crater is one of six potential landing sites now under evaluation.
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