Rather than assuming that modern Mars is too cold and dry to sustain liquid water, new evidence is challenging that belief. Data from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument has revealed unusually strong radar reflections coming from a region roughly 12 miles wide at the base of the planet’s southern polar ice cap.
These echoes are unlike any previously recorded in the area and resemble the signatures scientists would expect from liquid water trapped beneath layers of ice.
If confirmed, the finding would overturn long-standing assumptions about Mars’ current climate conditions and reopen major questions about whether the planet still harbors environments capable of supporting microbial life.
‘Dry’ materials could mimic signs of a buried lake on Mars
Despite the excitement surrounding the radar signals, researchers caution that liquid water beneath Mars’ south polar ice would be difficult to maintain under the planet’s extreme cold. Without highly salty brines or pockets of geothermal heat, sustaining water in liquid form seems unlikely.
That is why scientists are actively evaluating alternative “dry” explanations for the strong reflections detected by MARSIS, including layered deposits of carbon dioxide and water ice, or combinations of salty ice and clay that could boost radar reflectivity without requiring the presence of an actual underground lake.
To verify the MARSIS findings, scientists are now using the Shallow Radar (SHARAD) on the Mars Reconnaissance Orbiter. SHARAD operates at higher frequencies but previously couldn’t reach deep enough to scan the base of the southern ice cap. That changed after the orbiter team tested a new maneuver that rolls the spacecraft 120° along its flight axis – far beyond the old 28° limit – allowing SHARAD to aim its radar deeper and potentially detect the same reflections observed by MARSIS.
New technique helps scientists investigate mysterious south pole radar echoes
Rather than relying on its standard orientation, mission controllers are now using a technique called a “very large roll” (VLR) to boost SHARAD’s capabilities. By tilting the spacecraft far more than usual, the VLR maneuver increases the strength and depth of SHARAD’s radar signal, giving scientists a clearer look at the base of the ice in the puzzling high-reflectivity region.
In a recent study published in Geophysical Research Letters, Gareth Morgan and his team analyzed 91 SHARAD observations that passed directly over this zone in an effort to determine what is causing the unusual radar echoes.
Rather than confirming the presence of liquid water, the latest SHARAD tests point elsewhere. A basal echo appeared only during the VLR maneuver, and even then the signal was very weak – unlike the strong reflections seen by MARSIS. This suggests liquid water is unlikely in the high-reflectivity zone.
The research team noted that the faint signal is more consistent with a smooth patch of ground beneath the ice, and further work is needed to understand why SHARAD and MARSIS show such different results.