Giant Mars crater shows evidence of ancient lake

The new information comes from researchers analysing spectrometer data from NASA's Mars Reconnaissance Orbiter (MRO), which looked down on the floor of McLaughlin Crater.

The Martian crater is 92 kilometres in diameter and 2.2 kilometres deep. McLaughlin's depth apparently once allowed underground water, which otherwise would have stayed hidden, to flow into the crater's interior, NASA said.

Layered, flat rocks at the bottom of the crater contain carbonate and clay minerals that form in presence of water.

McLaughlin lacks large inflow channels, and small channels originating within the crater wall end near a level that could have marked the surface of a lake.

These new observations suggest the formation of the carbonates and clay in a groundwater-fed lake within the closed basin of the crater.

Some researchers propose the crater interior catching the water and the underground zone contributing the water could have been wet environments and potential habitats, according to the study published in Nature Geoscience.

"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 study.

Michalski checked for minerals such as carbonates, which are best preserved under non-acidic conditions.

"New results like this show why that effort is so important," said CRISM Principal Investigator Scott Murchie of Johns Hopkins University Applied Physics Laboratory.

Launched in 2005, MRO and its six instruments have provided more high-resolution data about the Red Planet than all other Mars orbiters combined.

"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.

"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," Michalski said.

McLaughlin Crater sits at the low end of a regional slope several hundreds of miles long on the western side of the Arabia Terra region of Mars. As on Earth, groundwater-fed lakes are expected to occur at low regional elevations. This site would be a good candidate for such a process.