NASA's Mars Reconnaissance Orbiter Reveals Insights into Martian Subsurface Water

NASA's Mars Reconnaissance Orbiter (MRO) has made significant advancements in understanding the Martian subsurface, particularly regarding the existence of a suspected underground lake. A recent study published in *Geophysical Research Letters* on November 17, led by Gareth Morgan and Than Putzig from the Planetary Science Institute, utilized the orbiter's Shallow Radar (SHARAD) instrument to enhance radar signal penetration beneath the Martian surface. This was achieved through a specialized maneuver that involved rolling the spacecraft 120 degrees, allowing for clearer imaging of subsurface structures.

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Prior to this breakthrough, multiple attempts to detect signals from the area believed to host the buried lake had been unsuccessful. The SHARAD team collaborated with NASA's Jet Propulsion Laboratory (JPL) to develop the very large roll capability, which was crucial for improving the radar's sensitivity. The MRO's design, with its radar antenna positioned at the rear, initially obstructed the instrument's view. Engineers from JPL and Lockheed Martin Space devised commands for the 120-degree roll, which was executed on May 26. This maneuver successfully detected radar signals from a region approximately 12.5 miles (20 kilometers) wide, buried under nearly one mile (1,500 meters) of water ice.

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The radar signals detected by SHARAD indicate the presence of a reflective surface, suggesting the existence of liquid water beneath the ice. Unlike other materials that absorb or weaken radar signals, liquid water reflects them strongly, akin to a flashlight beam hitting a mirror. This finding aligns with previous observations made by the European Space Agency's Mars Express orbiter, which identified a similar signal in 2018. Scientists propose that the liquid water could exist as a briny lake, where high salt concentrations lower the freezing point of water, allowing it to remain in a liquid state despite the surrounding ice.

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While the findings are promising, some scientists remain cautious about the interpretation of the radar signals. Critics argue that further validation is necessary to confirm the existence of liquid water and to understand the geological processes that could allow such bodies to exist beneath thick ice layers.

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NASA officials have expressed enthusiasm about the new capabilities of the MRO and the potential for future explorations. The successful implementation of the very large roll technique is seen as a pivotal step in the ongoing investigation of Mars' subsurface environment.

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• “These “very large rolls” have proved so effective that scientists are eager to use them at previously observed sites where buried ice might exist.” — Gareth Morgan, SHARAD Scientist

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• “Liquid water is special in that it produces a very reflective surface, sending back a very strong signal (imagine pointing a flashlight at a mirror).” — NASA Official

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The MRO team plans to utilize the very large roll technique at additional sites on Mars to further investigate the potential for subsurface water and its implications for understanding the planet's climate history and habitability.

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