Although no direct evidence of life has been discovered on Mars, a recent NASA study suggests that microbes might survive beneath frozen water on the planet’s surface.
Using computer modeling, the researchers demonstrated that sunlight penetrating the water ice could support photosynthesis in shallow meltwater pools just below the ice. On Earth, similar sub-ice pools are home to diverse life forms, such as algae, fungi, and microscopic cyanobacteria, which all rely on photosynthesis for energy.
“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,” said the paper’s lead author, Aditya Khuller of NASA’s Jet Propulsion Laboratory in Southern California.
Mars has two types of ice: water ice and carbon dioxide ice. In a study published in Nature Communications Earth & Environment, Khuller and colleagues focused on water ice, which formed from snow and dust that accumulated on the surface during Martian ice ages over the past million years. This ancient snow has since compressed into ice, still containing traces of dust.
While dust particles can block light in deeper ice layers, they may actually help create subsurface pools of water when exposed to sunlight. The dark dust absorbs more heat than the surrounding ice, potentially warming it enough to cause melting just a few feet below the surface.
There is debate among Mars scientists about whether ice can truly melt on the Martian surface. Mars has a thin, dry atmosphere, where water ice typically sublimates—changing directly from solid to gas, much like dry ice on Earth. However, below the surface of a dusty snowpack or glacier, these atmospheric conditions wouldn’t inhibit melting in the same way.
On Earth, dust embedded in ice can form features known as cryoconite holes—small cavities that develop when windblown dust particles (called cryoconite) settle on the ice, absorb sunlight, and gradually melt deeper into the ice each summer. Eventually, as the particles sink away from direct sunlight, they reach a depth where they no longer descend, but still produce enough warmth to create small pockets of meltwater around them. These pockets can sustain a rich ecosystem, supporting simple life forms.
“This is a common phenomenon on Earth,” said co-author Phil Christensen of Arizona State University in Tempe, 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.”
Christensen, a longtime researcher of Martian ice, oversees NASA’s THEMIS (Thermal Emission Imaging System) on the 2001 Mars Odyssey orbiter. In prior work with Gary Clow from the University of Colorado Boulder, Christensen used modeling to show how liquid water could form within Mars’ dusty snowpack—a study that laid the groundwork for the latest research on whether photosynthesis might be possible on the planet.
In 2021, Christensen and Khuller co-authored a paper on dusty water ice exposed in Martian gullies, suggesting that erosion caused by melting ice could explain many of these formations. The new study proposes that light could penetrate dusty ice on Mars down to depths of 9 feet (3 meters), allowing photosynthesis to occur in shallow subsurface meltwater pools. The upper ice layers would shield these pools from evaporation and harmful radiation, a crucial factor since Mars lacks Earth’s magnetic field to protect it from solar and cosmic radiation.
The authors suggest that subsurface water pools would be most likely to form in Mars’ tropical regions, between 30 and 60 degrees latitude in both hemispheres. Next, Khuller aims to recreate Mars’ dusty ice conditions in a lab for closer examination. Meanwhile, he and other scientists are mapping potential sites on Mars where shallow meltwater might be found—locations that could be ideal targets for future human and robotic exploration.
