“Follow the water” has long been the mantra of scientists searching for life beyond Earth. After all, the only known birthplace of life in the cosmos is the aquatic planet we call home. But now there’s more evidence to suggest that a potential discovery of liquid water on Mars maybe not so waterproofresearchers report September 26 to natural astronomy.
In 2018, scientists announced the discovery of a large underground lake near the south pole of Mars (SN: 07/25/18). This claim – and follow-up observations suggesting additional inground pools of liquid water on the red planet (SN: 09/28/20) – fueled the excitement of finally finding an extraterrestrial world possibly suitable for life.
But researchers have since proposed that these findings may not hold up to scrutiny. In 2021, a group suggested that clay minerals and frozen brinesrather than liquid water, may be responsible for the strong radar signals observed by the researchers (SN: 07/16/21). The spacecraft orbiting Mars beams radio waves toward the Red Planet and measures the timing and intensity of the reflected waves to infer what lies beneath the Martian surface.
And now another team has shown that ordinary layers of rock and ice can produce many of the same radar signals previously attributed to water. Planetary scientist Dan Lalich of Cornell University and his colleagues have calculated how flat layers of bedrock, water ice, and carbon dioxide ice — all known to be abundant on Mars — reflect radio waves. “It was a pretty straightforward analysis,” Lalich says.
The researchers found they could reproduce some of the abnormally strong radar signals thought to be due to liquid water. Individual radar signals from different layers of rock and ice add up when the layers are of a certain thickness, Lalich says. This produces a stronger signal, which is then picked up by a spacecraft’s instruments. But these instruments can’t always tell the difference between a radio wave coming from one layer and one coming from multiple layers, he says. “They look like a reflection on the radar.”
These results do not exclude the presence of liquid water on Mars, acknowledge Lalich and his colleagues. “It just means there are other options,” he says.
The new discovery is “a plausible scenario,” says Aditya Khuller, a planetary scientist at Arizona State University in Tempe who was not involved in the research. But until scientists get a lot more data from the Red Planet, it will be unclear whether liquid water really exists on Mars, Khuller says. “It’s important to be open-minded at this stage.”