“Follow the water” has long been the mantra for scientists searching for life beyond Earth. After all, the only known cradle of life in the cosmos is the watery planet we call home. But now there is more evidence to suggest that a possible discovery of liquid water on Mars may not be so airtightresearchers report on September 26 in nature astronomy.
In 2018, scientists announced the discovery of a large underground lake near the south pole of Mars (Serial number: 7/25/18). That statement, and follow-up observations suggesting additional inground pools of liquid water on the red planetSerial number: 09/28/20), fueled the excitement of finally finding an alien world possibly conducive to life.
But since then, researchers have proposed that those discoveries might not stand up to scrutiny. In 2021, one group suggested that clay minerals and frozen brinesrather than liquid water, it could be responsible for the strong radar signals the researchers observed (Serial number: 7/16/21). Spacecraft orbiting Mars beam radio waves toward the Red Planet and measure the time and intensity of the reflected waves to infer what lies below 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 calculated how flat layers of bedrock, water ice, and carbon dioxide ice, known to be abundant on Mars, reflect radio waves. “It was a pretty simple analysis,” says Lalich.
The researchers found that they could reproduce some of the anomalously strong radar signals that were thought to be due to liquid water. Individual radar signals from different layers of rock and ice add up when the layers are a certain thickness, Lalich says. That produces a stronger signal, which is then picked up by a spacecraft’s instruments. But those instruments can’t always tell the difference between a radio wave that comes from one layer and one that’s the result of multiple layers, he says. “They look like a radar reflection.”
These results do not rule out liquid water on Mars, Lalich and his colleagues acknowledge. “This is just saying that there are other options,” he says.
The new finding 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 much more data from the Red Planet, it will be difficult to know if liquid water actually exists on Mars, says Khuller. “It’s important to keep an open mind right now.”