The surface of Mars is extremely cold, irradiated, and desiccated. But at one time, the planet was much warmer and wetter, with flowing water, lakes, and even an ocean covering most of its northern hemisphere. Because of this, scientists speculate that life may have emerged on Mars billions of years ago and could still be there today. Ever since the Viking 1 and 2 missions landed on the surface in 1976, the search for evidence of past (and maybe present) life has been ongoing.
As missions like Curiosity and Perseverance continue to explore promising regions that were once lakebeds (the Gale and Jezero craters), there are still questions about where to look next. In a recent paper, researchers proposed searching for photosynthetic bacteria embedded in the snow and ice around Mars’ mid-latitudes. Using “radiatively habitable zones” on Earth as a template, they argue that photosynthetically active bacteria could survive within exposed patches of ice.
The research was led by Dr. Aditya Khuller, a postdoctoral researcher at NASA’s Jet Propulsion Laboratory (JPL) and the University of Washington’s Polar Science Center (UW-PSC). He was joined by colleagues from the UW Applied Physics Laboratory, the School of Earth & Space Exploration at Arizona State University (SESE-ASU), and the Institute of Arctic and Alpine Research (InstAAR) at the University of Colorado Boulder (UC Boulder). The paper that detailed their findings was presented at the 56th Lunar Planetary Science Conference (2025 LPSC).
On Earth, bacteria can survive and thrive in ice, even at depths of several meters. Earth’s protective ozone layer protects these organisms from harmful ultraviolet (UV) radiation, allowing them to safely absorb what is known as photosynthetically active radiation (PAR). On Mars, which has a thin atmosphere (less than 1% of Earth’s) and no ozone layer, about 30% more damaging UV radiation reaches the surface. However, numerical modeling predicts ice and snow around the equator can melt below the surface.
The presence of this liquid water at these depths could make these subsurface environments the most easily accessible locations for future astrobiology missions. To investigate this possibility, the team developed a radiative transfer model (RTM) based on previous research that employs the Delta-Eddington method (a simplified means of calculating radiative fluxes). This model allowed them to simulate vertically-stacked layers of snow, ice, and Martian dust.
Since solar flux has not yet been measured within ice on Mars, the team employed glacier ice in Greenland as an analog. Their results showed that in all cases, most of the solar radiation is absorbed within the top few meters of the ice, but increases based on grain size. Overall, they found that solar radiation can reach a maximum depth of about 6.5 meters (21.3 ft) in clean ice. At the same time, biologically damaging UV penetrated to about 3 m (~10 ft) in clean granular, packed ice (firn). Their results also indicated that PAR penetration varied considerably based on the amount of dust in the ice.
For ice with 0.01% dust, PAR reached just 25 cm (~10 inches) below the surface, while the peak penetration depth of UV was reduced to about 7 cm (2.75 inches). For ice with 0.1% dust concentrations, this was reduced to only 5 cm (~2 inches), with a peak UV penetration of 1.5 cm (0.6 inches). Overall, they found that Mars may have radiatively habitable zones within exposed patches of mid-latitude ice at depths ranging from a few centimeters for dusty ice to several meters for cleaner ice.
On Earth, microbes require temperatures of more than -18 °C (-0.67 °F) for cell division to occur. Meanwhile, favorable solar radiative conditions and the presence of liquid water are required for photosynthesis. And while conditions within the Martian polar ice are too cold for melting to happen at these depths, numerical models suggest that small amounts of melt and runoff can occur in exposed patches of mid-latitude snowpack just beneath the surface. As the team indicates, this could have significant implications in the search for life on Mars:
“Under similar ephemeral near-freezing conditions, widespread microbial habitats containing cyanobacteria, chlorophytes, fungi, diatoms, and heterotrophic bacteria are found in the shallow subsurface (top few centimeters to meters) of ice sheets, glaciers, and lake ice containing dust and sediment on Earth.
“In the summer, ice in the shallow subsurface melts due to solar heating at these locations. Photosynthesis then occurs in the subsurface, below a translucent ice lid, with nutrients scavenged from the dust and sediment present in the subsurface liquid water. During winter, the subsurface liquid refreezes, and photosynthesis ceases until the next summer.”
Therefore, if ice and snow in equatorial regions experience seasonal melting, microbes like cyanobacteria could combine this water with nutrients from Martian dust in the ice to conduct photosynthesis. If such habitats exist, they would constitute the most easily accessible locations for finding evidence of life on Mars.
Further Reading: USRA