New Signs of Recent Water
Summary (Jun 02, 2002): Piles of crater-topped debris snapped by NASA's Mars orbiter and caused by the teakettle explosion of water through volcanic lava flows at the planet's equator are the best evidence yet for recent liquid water at the Red Planet, a team of scientists say.
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New Signs of Recent Water
By SPACE.com Staff Piles of crater-topped debris snapped by NASA's Mars orbiter and caused by the teakettle explosion of water through volcanic lava flows at the planet's equator are the best evidence yet for recent liquid water at the Red Planet, a team of scientists say.
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A simulated image of the new Mars rover carrying the Athena science instruments.
Credit: NASA |
Under a model devised by the University of Arizona and University of Hawaii researchers, the "rootless cones" formed after volcanic eruptions melted frozen water near the surface of Mars 10 million years ago -- practically present time in the geological view. The melting caused floods that carved channels and seeped into the ground.
"We think lava flows have advanced over the wet ground causing steam explosions that built these rootless cones," said Laszlo Keszthelyi, a senior research associate at Arizona's Lunar and Planetary Laboratory. "It means Mars is not dead geologically. Volcanic eruptions and water floods are something ongoing into the current geologic era."
The finding, published this week in Geophysical Research Letters, follows two findings from last year showing signs of liquid water at Mars. But some geologists think the features in question in those past studies can be explained by liquid carbon dioxide, not liquid water.
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"If something like Ma'adim Vallis (above) is actually a lava flow and looks so much like a fluvial channel, well, we better reassess what we think about the channels we're seeing on Mars." -Nathalie Cabrol
Credit: R. Irwin III (CEPS/NASM,UVa), T. Maxwell, A. Howard, R. Craddock, D. Leverington |
Keszthelyi is confident that the debris cones in the his team's work are the result of liquid water exploding through lava. "The area is just too warm to have CO2 stick around," he said. Temperatures and surface pressures at the equator provide the right recipe for liquid water unlike the conditions at sites identified in past studies as showing evidence of liquid water.
There is water frozen into Mars' polar caps. Scientists have known this for a while. But that water is locked in a vapor-ice cycle, never liquifying. So signs of liquid water, especially distant from Mars' poles, excites researchers looking for conditions suitable for life. In fact, there could be liquid water at Mars right now, said Keszthelyi's colleague Alfred S. McEwen.
Water in upper 10 meters today
The cones were found in the Cerberus plains, Marte Valles and Amazonis Planitia regions near Mars' equator by studying high-resolution images taken by the camera on Mars Global Surveyor, which has been orbiting the planet for the past four years. The researchers say the lava was flowing over ice no deeper than 5 meters (15 feet) below the surface.
"If ground ice was present within 5 meters of the surface only a few million years ago, it is very likely to persist today within about the upper 10 meters," said McEwen, a University of Arizona planetary scientist.
The Martian cones, ranging from house-sized to small stadium-sized, resemble similar features in Iceland which form when surface lava interacts explosively with near-surface groundwater.
Thorvaldur Thordarson of the University of Hawaii, who has done fieldwork in Iceland, says rootless cones form where molten lava flows over marshy terrain.
A crust forms over the lava flow, while molten lava continues to pump through tubes or pathways beneath the crust. As lava is shoved through the tubes, it mixes with some of the underlying water-rich sediment, and in the process of mixing, the water is heated by lava until it flashes to steam.
When the steam pressure exceeds the pressure of the lava above it, there's a "phreatomagmatic" -- or groundwater and magma -- explosion. The result of several such sustained explosions is a cluster of cones associated not with any deep fault or fissure but with a network of lava tubes over the marshy area.
If Mars is like Earth
"We see many hundreds of similar cones in the Mars [landscape], and they appear to be associated either with low plains areas or with recent outflow channels," said Peter D. Lanagan, also of the LPL. Water would flow to low areas, pond and percolate in low plains during the floods, recharging ground ice.
"If the terrestrial rootless cone analogy is extended to Mars," he said, "lava flows erupted over surfaces with ground ice -- probably at a depth of less than 5 meters -- where they melted the ice to form a water-rich slurry which mixed with the tube-fed lavas. The process likely would have resulted in a series of phreatomagmatic explosions, which formed cones on the top of the chilled lava crust.
"The Martian cones are close to outflow channels, so the cones formed in regions that were probably water- or ice-rich," Lanagan said.
Where did the ice come in?
There are three scenarios that various scientists argue for the source of the shallow water ice that exploded to bust through the lava and form the cones. It could be leftover from the planet's formation, it could have condensed from vapor in the atmosphere, or it could be the result of surface flooding.
The University of Arizona and University of Hawaii team votes for a combination of the condensation and flooding explanations.
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Mars Life: [6-25-2001]
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Sunday, June 02, 2002
