The European Space Agency’s Mars Express spacecraft has been orbiting Mars since 2003, and is equipped with radar to map the Martian subsurface. In 2018 researchers working on the project announced a remarkable discovery. They reported observations of radar reflections from lakes of liquid water sealed underneath the ice of the Martian south polar cap.
On Earth, subglacial lakes are fairly common. More than four hundred have been found in Antarctica. While there’s lots of evidence that liquid water existed on Mars in the distant geological past, the radar finding was exciting because it implied that liquid water still exists on Mars today.
The lakes seemed like a great place to search for Martian life. But from the beginning, there were doubters, who noted that only a source of volcanic heat could keep the water from freezing solid in the extreme Martian cold. Modern Mars lacks volcanic activity.
In 2021 three teams of researchers based in North America published research casting further serious doubts on the existence of Martian lakes. The new analysis showed the radar signatures to be more abundant than previously thought, making it even harder to explain how all those lakes could persist in the Martian cold.
The radar signature of liquid water is strong and distinctive, because of its electrical properties. Still, the researchers came up with several other possibilities that could mimic the signal produced by water, including clay minerals, or salty frozen brine. Geologists already know that clay minerals exist on Mars. Their existence is itself evidence that liquid water once existed on Mars in the past. Detecting underground water on other planets and moons may be harder than scientists thought.
Reviewer: Alexis Shakas, ETH Zurich, Zurich, Switzerland
Read more
- The freezing and flowing waters of Mars
- Tsunamis and the oceans of Mars
- Thiophenes on Mars: evidence of past life?
Sources
- ScienceNews - Lakes of liquid water at Mars' southern ice cap may just be mirages
- Vice - Lakes on Mars may be a mirage, scientists say
- Scientific American - Buried 'lakes' on Mars may just be frozen clay
- NASA - Clay, not water, are likey source of Mars 'lakes'
- Geophysical Research Letters - Strong MARSIS radar reflections from the base of Martian south polar cap may be due to conductive ice or minerals
- Geophysical Research Letters - Characteristics of the Basal Interface of the Martian South Polar layered deposits
- Geophysical Research Letters - A solid interpretation of bright radar reflectors under the Mars south polar ice
The European Space Agency’s Mars Express spacecraft has been orbiting Mars since 2003, and is equipped with radar to map the Martian subsurface. In 2018 researchers working on the project announced a remarkable discovery. They reported observations of radar reflections from lakes of liquid water sealed underneath the ice of the Martian south polar cap.
On Earth, subglacial lakes are fairly common. More than four hundred have been found in Antarctica. While there’s lots of evidence that liquid water existed on Mars in the distant geological past, the radar finding was exciting because it implied that liquid water still exists on Mars today.
The lakes seemed like a great place to search for Martian life. But from the beginning, there were doubters, who noted that only a source of volcanic heat could keep the water from freezing solid in the extreme Martian cold. Modern Mars lacks volcanic activity.
In 2021 three teams of researchers based in North America published research casting further serious doubts on the existence of Martian lakes. The new analysis showed the radar signatures to be more abundant than previously thought, making it even harder to explain how all those lakes could persist in the Martian cold.