River-Size "Flash Floods" May Have Carved Mars Craters

Anne Minard
for National Geographic News

February 20, 2008

Using a classroom-size prop, a team of Dutch researchers says it may have demystified a handful of unusual Martian craters—and further complicated the story of the red planet's watery early years.

The team's new paper proposes that enormous amounts of water gushed out of the Martian interior and filled the oddly terraced craters in a torrent.

Each rare event would have lasted on the order of decades, not the centuries or millennia proposed for other water-carved features on the planet's surface.

"On Earth it would look like the Mississippi River or the Rhine River turning on from a single source and flowing for between ten and one hundred years and then just shutting off," said lead author Erin Kraal, who is now at Virginia Polytechnic Institute and State University.

Because there are no drainage networks on the surface of Mars, the study authors believe an unknown geological process triggered the huge releases of water.

(Related: "Mars Water Traces Left by Springs, Not Seas, Experts Say" [March 7, 2007].)

The findings, which are being met with a mix of excitement and skepticism, appear in tomorrow's issue of the journal Nature.

Sudden Rush

Among the many craters that characterize the Martian surface, some are basins with fan-shaped raised patterns at their bottoms.

Starting about three years ago, researchers began noticing that a handful of these fanned craters—ten so far—have a distinctive stair-like set of terraces.

But until now, how these odd patterns formed was a puzzle.

So Kraal, while working at her previous job in Utrecht University in the Netherlands, led a team that built an indoor flume that mimicked the Martian basins.

When water was put into a short, adjacent channel, the liquid pulled sediment out of the channel and transferred it into the basin.

But unlike the uniform deposits seen where rivers dump into lakes on Earth, the high volume of water sent the sediment out into sequentially wider layers as it advanced, forming the steps.

For that scenario to work, the water would have to come in a sudden rush—and it could happen only once per basin.

"We suggest that the water was released internally, such as a hydrothermal water source suddenly pushed to the surface," Kraal said.

(Related: "Mars's Water Could Be Below Surface, Experts Say" [January 25, 2007].)

Not So Fast

Alan Howard, a University of Virginia researcher, noted that fan-shaped features occur in other settings—including when Earth's rivers empty into lakes or the ocean.

"There is little other direct evidence of former lakes on Mars, although many Mars researchers, including myself, feel that lakes were numerous during early Martian history," he said.

But Howard isn't convinced that the floods happened quickly, only once, or from single sources of water. He believes water could have seeped into the basins from a variety of sources or could have come from precipitation.

At least one other researcher is happy to see the new findings, though.

"This paper could go a long way toward convincing the community that water-flow events on early Mars may have been short-lived and catastrophic," said Douglas Jerolmack, a researcher at the University of Pennsylvania.

He understands that skeptics will want to wait until the findings are backed up with detailed sediment transport models, which can only come from closer looks at the surface of Mars, he said.

Satellites could do the trick, he added—but he's hoping for another rover.

Study leader Kraal said further support for the new findings could also come from elsewhere in the solar system.

On Earth, she pointed out, depositional features are often shrouded by vegetation and therefore tough to study.

But Saturn's moon Titan, for instance, is a little more like Mars in that its surface is exposed—and it also boasts fan-shaped craters.

There, she noted, "the fundamental variables—gravity, the type of rock, the atmosphere—are so different.

"It is interesting to change the fundamental variables and look at such processes," she said.

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