While Mars Rover Curiosity is busy drilling rocks, NASA‘s Mars Reconnaissance Orbiter (MRO) has provided new evidence of a possibly wet underground environment on Mars.

The new evidence comes from Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data of a location known as McLaughlin Crater. The crater, which is 92 kilometers (57 miles) in diameter and 2.2 kilometers (1.4 miles) deep, appears to have once held a lake that was fed by groundwater. Researchers looking at the data point to layered, flat rocks at the botom of the crater conaining carbonate and clay minerals as evidence of the ancient lake. However, the lack of large inflow channels mean the source of the lake must have come from below.

“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 a paper on the findings published this week in the journal Nture Geoscience. “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.”

On Earth, groundwater-fed lakes usually occur at low elevations. McLaughlin Crater sits at the low end of a regional slope several kilometers long, meaning it fits the profile for such a process.

“The MRO team has made a concerted effort to get highly processed data products out to members of the science community like Dr. Michalski for analysis,” said Scott Murchie, CRISM Principal Investigator at the Johns Hopkins University Applied Physics Laboratory. “New results like this show why that effort is so important.”