Recent studies have cast doubt on the existence of a liquid water lake beneath the ice cap at the south pole of Mars, a discovery that initially raised hopes of finding microbial life on the Red Planet.
In 2018, the European Space Agency’s Mars Express satellite detected strong radar reflections suggesting a 12-mile-long lake beneath the surface of Mars. However, new research from Cornell University provides a less dramatic but comprehensive explanation for these radar signals, showing that they may be due to natural interference of radar waves rather than liquid water.
Investigation of radar reflections
The initial excitement stemmed from radar data collected by the Mars Express satellite that revealed bright reflections from beneath the south polar ice cap, similar to those seen in subglacial lakes on Earth. These considerations led scientists to hypothesize the existence of a liquid water lake, potentially harboring microbial life.
Supporting this hypothesis, researchers from the University of Cambridge found patterns in the surface ice consistent with a subglacial lake. However, recent simulations conducted by Cornell researchers suggest that small variations in the composition and thickness of ice layers can produce similar radar reflections without the presence of liquid water.
Daniel Lalich, a research associate at the Cornell Center for Astrophysics and Planetary Sciences and lead author of the new study, argues that the radar signals can be explained by constructive interference of radar waves. “I can’t say it’s impossible to have liquid water down there, but we’re showing that there are much simpler ways to get the same observation without having to go so far, using mechanisms and materials to which we already know exist there.’
“But just by random chance you can create the same observed signal in the radar,” Lalich said.
It is known to exist at the Martian poles, changing the composition and spacing of ice sheets. The results suggest that the observed bright reflections may be produced by these natural variations in the ice.
Lalich elaborates: “Just by chance you can create the same observed signal in the radar. This is the first time we have a hypothesis that explains the entire body of observations under the ice cap without having to introduce anything unique or strange. “
The new discoveries
The new research provides a detailed and more realistic model to explain the bright radar reflections originally thought to indicate liquid water. By simulating different layering scenarios, the team demonstrated that small variations in ice composition and layer thickness can lead to constructive interference with radar waves, amplifying their reflections. These reflections, although similar to those produced by liquid water, do not necessarily indicate its presence.
Lalich’s study, titled “Small Variations in Ice Composition and Layer Thickness Explain Bright Reflections Beneath the Liquid Water-Free Martian Polar Cap,” published in Scientific progress, outlines how bright radar signals can be produced by known materials and conditions on Mars. “The idea that there would be liquid water even somewhat close to the surface would be really exciting,” Lalich said. “I just don’t think it’s there.”
Implications for the search for life on Mars
The potential existence of liquid water on Mars is an attractive prospect because it raises the possibility of microbial life. While robotic explorers such as NASA’s Perseverance rover have provided extensive evidence of ancient water flows on the Martian surface, current conditions at the poles make the existence of liquid water unlikely. The temperature and pressure on Mars are significantly different from those on Earth, complicating the possibility of liquid water existing beneath the ice caps.
Nevertheless, the search for life on Mars continues. Scientists are exploring other regions and using advanced technology to find signs of past or present life. The new Cornell study underscores the importance of considering simpler explanations and thorough hypothesis testing before concluding that liquid water exists. Lalich’s findings suggest that the bright radar reflections may be caused by natural variations in the ice, rather than requiring the presence of liquid water.
The Cornell study has sparked debate in the scientific community, with some researchers expressing skepticism. “The Cambridge scientists said they had not seen the new research, but said the unusual patterns they found on the surface could not be explained by radar interference,” the Cambridge team said in a statement.
While this new understanding may reduce the likelihood of finding liquid water at the south pole of Mars, it does not diminish the importance of continued research. Robotic missions and future human explorers will still play a crucial role in unlocking the secrets of Mars and assessing its habitability. The Perseverance rover, for example, is currently exploring an ancient river delta in the Jezero crater, which could provide valuable clues about the planet’s aquatic past and its potential to support life.
