The long-standing mystery of potential water beneath the Martian south pole has taken a dramatic turn. New findings from NASA's Mars Reconnaissance Orbiter (MRO) suggest that a feature once thought to be a vast underground lake is more likely a deposit of volcanic rock and dust.
New Radar Technique Overturns Lake Hypothesis
This revelation stems from a sophisticated radar analysis published on November 17 in the journal Geophysical Research Letters. The research, led by scientists Gareth Morgan and Than Putzig, utilized the Shallow Radar (SHARAD) instrument on the MRO. The initial excitement began in 2018 when the European Space Agency's Mars Express orbiter, using its MARSIS instrument, detected a highly reflective signal deep under the ice. Scientists theorized this bright echo could indicate a briny subsurface lake, a discovery that sparked intense debate about the potential for life.
For years, the SHARAD team struggled to observe the same area. The breakthrough came through a daring spacecraft manoeuvre. On May 26, engineers at Lockheed Martin Space, which built the orbiter, commanded the MRO to execute a 120-degree roll. This "very large roll" allowed the SHARAD radar to focus its signal more effectively towards the surface, enabling it to penetrate nearly 1 mile (1,500 meters) of water ice to image a target area spanning about 12.5 miles (20 km).
Deeper Imaging Reveals a Different Story
The results were telling. While water typically creates a strong, mirror-like radar reflection, SHARAD captured only a faint signal from the depths, in stark contrast to the bright signal previously noted by MARSIS. An additional observation in a nearby area found no signal at all, suggesting something unique at the specific MARSIS detection site.
"The lake hypothesis was a tremendous catalyst for creative scientific inquiry," noted Morgan. However, he emphasized that the new data challenges the theory of a liquid water lake, underscoring the evolving nature of planetary science. The scientists now speculate that the bright MARSIS signal may have come from an unusually smooth area, perhaps an ancient lava flow, nestled beneath the heavily cratered terrain of the south polar ice cap.
Implications for Future Mars Exploration
While dashing hopes for a readily accessible body of liquid water, the findings highlight the power of the new radar technique for identifying subsurface resources. The team is eager to apply the same large roll manoeuvre to other enigmatic regions of Mars. A prime target is Medusae Fossae, a massive geological formation near the Martian equator.
There are competing theories about Medusae Fossae's composition; some scientists believe it is made of volcanic ash, while others suspect it could contain significant amounts of ice. "If ice exists there, it hints at abundant water resources near the equator," explained Putzig. This location is considered ideal for future human missions due to its warmer temperatures, greater sunlight exposure, and overall suitability for habitation. The quest to map Mars's hidden water ice continues, now armed with a more powerful tool.
