Flash Floods May Gush Through Martian Canyons
(From the September/October 2000 issue of StarDate magazine)
Torrents of muddy water may rush down the interior walls of Martian craters and valleys, carving deep gullies and depositing fan-shaped layers of debris that look like small river deltas, according to researchers who study images of the planet snapped by the Mars Global Surveyor spacecraft. At the same time, analysis of a Martian meteorite suggests there may be two to three times more water locked in the Martian crust than previously expected. The findings hint that large reservoirs of liquid water may lie not far below the Martian surface, enhancing the chances that microscopic life may inhabit the planet.
Global Surveyor images reveal gullies in several hundred locations around the planet. Most are found along the sides of tall cliffs in valleys or craters. Mariner 9 and the Viking 1 and 2 orbiters of the 1970s had already found large dry riverbeds scattered across Mars, but those channels probably have not carried water in billions of years.
The gullies discovered by Global Surveyor are much smaller -- generally no more than a few hundred to a few thousand yards long, but they have not been covered by wind-blown dust or scarred by impact craters, like the larger channels, suggesting that they are very young. "They could be a few million years old, but we cannot rule out that some of them are so recent as to have formed yesterday," said Michael Malin, principal investigator for the Mars Orbiter Camera.
Scientists say a gully probably formed when water from an aquifer a few hundred feet below the surface burst through the cliff side. In the cold, thin Martian atmosphere, the first gush of water probably froze, creating a strong "ice dam." Over time, though, water pressure burst the dam and the water flowed downhill in a great flood, mixing with the Martian soil to form a muddy channel. This debris spread out at the bottom of the slope, depositing a fan-shaped layer at the end of the channel.
Since water is an essential ingredient for life as we know it, the possible discovery of a current source of liquid water on Mars enhances the possibility that life evolved on the planet in the past and still exists today. In addition, future Mars explorers could use the water for drinking and to make rocket fuel.
Analysis of a Martian meteorite found in Antarctica in 1994 suggests there could be much more water in the crust of Mars than scientists had expected. Laurie Leshin of Arizona State University compared the amount of "heavy" hydrogen found in Martian meteorite QUE 94201 with the amount found in the planet's atmosphere. Scientists had estimated that only 10 percent of the water originally found in the Martian atmosphere and upper crust still remained on the planet. But the heavy-hydrogen content in the meteorite suggests that as much as 20 to 30 percent of the water may remain. -- — Damond Benningfield
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