“Follow the water” has long been the mantra of scientists searching for life beyond Earth. The only known cradle for life in the cosmos, after all, is the planet we call home. But now there’s more evidence suggesting that a potential discovery of liquid water on Mars It might not be as simple as it seemsResearchers report September 26th Astronomy in Nature.
2018 was a year of announcements by scientists the discovery of a large subsurface lake near Mars’ south pole (SN: 7/25/18). That claim — and follow-up observations suggesting Additional buried pools of liquid are also availableRed Planet (SN: 9/28/20) — fueled excitement about finally finding an extraterrestrial world possibly conducive to life.
However, researchers have suggested that the findings might not stand up to scrutiny. One group proposed that 2021 would be the year. Clay minerals and frozen brinesResearchers believe that radar signals are more likely to be generated by solid water than liquid.SN: 7/16/21). Spacecraft orbiting Mars beam radio waves toward the Red Planet and measure the timing and intensity of the reflected waves to infer what’s beneath the Martian surface.
Another team now shows that ordinary layers like rock and ice can produce radar signals similar to those previously thought to be due water. Planetary scientist Dan Lalich of Cornell University and his colleagues calculated how flat layers of bedrock, water ice and carbon dioxide ice — all known to be plentiful on Mars — reflect radio waves. “It was a pretty simple analysis,” Lalich says.
Researchers discovered that they were able to reproduce certain anomalously strong radar signals believed to be caused by liquid water. Lalich says that individual radar signals from different layers can add up when the layers have a certain thickness. 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 coming from one layer and one that’s the result of multiple layers, he says. “They look like one reflection to the radar.”
These results don’t 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 a lot more data from the Red Planet, it’ll be difficult to know whether liquid water truly exists on Mars, Khuller says. “It’s important to be open-minded at this point.”
