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Layers with carbonate content inside McLaughlin Crater on Mars . Image Credit: NASA/JPL/Caltech Univ. of Arizona Layers with carbonate content inside McLaughlin Crater on Mars . Image Credit: NASA/JPL/Caltech Univ. of Arizona

Martian crater holds carbonate clues to an ancient lake

Sen— NASA's Mars Reconnaissance Orbiter has found evidence that a lake may once have existed in a Martian crater, fed from underground water.

McLaughlin Crater is 57 miles (92 kilometers) in diameter and 1.4 miles (2.2 kilometers) deep. It lies west of the Arabia Terra region of Mars at the low end of a regional slope several hundred miles long. Studies of this crater are providing new evidence of underground water on Mars, adding a picture of the planet's early evolution.

As on Earth, groundwater-fed lakes are expected to occur at low regional elevations. Therefore, this site is a good candidate to have once had underground water which flowed into the crater's interior, forming a lake retained within the closed basin of the crater. Such an environment increases the chances of life having existed there in the past.

Researchers analyzing spectrometer data from NASA's Mars Reconnaissance Orbiter (MRO), which looked down on the floor of McLaughlin Crater, discovered layered flat rocks at the bottom of the crater that contain carbonate and clay minerals that form in the presence of water. There are no large inflow channels, but small channels within the crater wall end near a level that could have marked the surface of a lake.

"Taken together, the observations in McLaughlin Crater provide the best evidence for carbonate forming within a lake environment instead of being washed into a crater from outside," said Joseph Michalski,lead author of the paper, which has five co-authors to be published in Sunday's online edition of Nature Geoscience. Michalski also is affiliated with the Planetary Science Institute in Tucson, Arizona, and London's Natural History Museum.

Since its launch in 2005 the Mars Reconnaissance Orbiter and its six instruments have provided more high-resolution data about the Red Planet than all other Mars orbiters combined. Data is made available for scientists worldwide to research, analyze and report their findings.

The team used the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on the Mars Reconnaissance Orbiter to check for minerals such as carbonates, which are best preserved under non-acidic conditions.

"A number of studies using CRISM data have shown rocks exhumed from the subsurface by meteor impact were altered early in Martian history, most likely by hydrothermal fluids," Michalski said. "These fluids trapped in the subsurface could have periodically breached the surface in deep basins such as McLaughlin Crater, possibly carrying clues to subsurface habitability."

"This new report and others are continuing to reveal a more complex Mars than previously appreciated, with at least some areas more likely to reveal signs of ancient life than others," said Mars Reconnaissance Orbiter Project Scientist Rich Zurek of NASA's Jet Propulsion Laboratory, Pasadena, California.

The Mars Reconnaissance Orbiter, which carries six instruments for studying the Red Planet, is managed by NASA's Jet Propulsion Laboratory (JPL), a division of the California  Institute of Technology.  The MRO launched on August 12, 2005 and entered orbit in 2006.

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