Mars is often considered a barren wasteland, with its thin atmosphere and intense ultraviolet radiation making the surface inhospitable for life as we know it. However, billions of years ago, the Red Planet could have had rivers, lakes, and even oceans. But as these favorable conditions vanished, any microbial life that existed might have retreated underground, where they could find shelter and resources.

A study from researchers at Caltech has identified habitable zones under Martian ice where conditions might be just right for life to persist. By calculating the depths at which photosynthetic microbes could find enough sunlight to survive while being protected from harmful radiation, the team has mapped out promising areas for future exploration.

Looking for Martian Life Beneath the Ice

The researchers focused on the potential for photosynthetic life to exist beneath layers of ice on Mars. They calculated that in ice containing between 0.01 and 0.1% dust, microbes could survive at depths between 5 and 38 centimeters (2 to 15 inches). In cleaner ice, the habitable zone could extend as deep as 2.15 to 3.1 meters (7 to 10 feet).

“Dark dust absorbs more sunlight than the surrounding ice, potentially causing the ice to warm up and melt up to a few feet below the surface,” explained Aditya Khuller of NASA’s Jet Propulsion Laboratory, the lead author of the study.

On the other hand, dust particles trapped within the ice could create localized pockets of meltwater, providing the liquid water necessary for life. This process is similar to phenomena observed on Earth, where dust within ice can cause melting from the inside out.

“This is a common phenomenon on Earth,” said co-author Phil Christensen of Arizona State University, referring to ice melting from within. “Dense snow and ice can melt from the inside out, letting in sunlight that warms it like a greenhouse, rather than melting from the top down.”

A New Target in the Search for Life

The study suggests that these habitable zones would most likely be found in Mars’ mid-latitudes, between approximately 30 and 50 degrees latitude, where conditions are suitable for this subsurface melting. The polar regions would be too cold for this process to occur.

While the existence of these theoretically habitable zones does not mean that life is present on Mars, it provides a promising target for future missions. “If we’re trying to find life anywhere in the universe today, Martian ice exposures are probably one of the most accessible places we should be looking,” Khuller said.

Armed with these findings that dramatically narrow down the range of possibilities, suddenly exploring Mars for life isn’t as daunting as before. Future robotic or crewed missions could focus on these areas, drilling into the ice to search for signs of life.

This search has been a driving force behind much of NASA’s exploration of the planet. From the Viking landers in the 1970s to the Perseverance rover currently traversing the Martian surface, scientists have been seeking signs of past or present life on Mars. So, by combining knowledge of Martian geology, climate, and the behavior of ice and dust, researchers are honing in on the most promising locations to search.

While there is no direct evidence yet, the possibility is intriguing. In the coming years, missions like the European Space Agency’s ExoMars rover and potential future NASA missions may have the opportunity to explore these habitable zones beneath the ice, bringing us closer to answering the age-old question: Is there life on Mars?

The findings appeared in the journal Nature Communications Earth & Environment.