Could life exist under the ice of Mars? Study suggests possibilities

Although real evidence of life on Mars has never been found, a new NASA study suggests that microbes could find a potential refuge beneath frozen water on the planet’s surface.

Using computer modeling, the study authors showed that the amount of sunlight that could shine through water ice would be enough for photosynthesis to occur in shallow pools of meltwater located beneath the surface of this ice. Similar pools of water that form in ice on Earth teem with life, including algae, fungi, and microscopic cyanobacteria, all of which get their energy from photosynthesis.

“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 look,” said the lead author of the study. article, Aditya Khuller of NASA’s Jet Propulsion Laboratory in Southern California.

Mars has two types of ice: frozen water and frozen carbon dioxide. For their article, published in Earth and Environment CommunicationsKhuller and his colleagues studied water ice, large quantities of which formed from snow mixed with dust that fell to the surface during a series of Martian ice ages over the past million years . This old snow has since solidified into ice, still dotted with grains of dust.

Although dust particles can obscure light in deeper layers of the ice, they are key to explaining how subsurface puddles could form in the ice when exposed to sunlight: dark dust absorbs more sunlight than the surrounding ice, potentially causing the ice to warm. and melt to a few feet below the surface.

Mars scientists are divided on whether ice can actually melt when exposed to the Martian surface. This is due to the planet’s thin, dry atmosphere, where water ice is thought to sublimate and turn directly into gas, as dry ice does on Earth. But the atmospheric effects that make melting difficult on the surface of Mars would not apply below the surface of a dusty snowpack or glacier.

Thriving microcosms

On Earth, dust in ice can create so-called cryoconite holes, small cavities that form in ice when wind-blown dust particles (called cryoconite) settle there, absorbing the sunlight and melt deeper into the ice each summer. Eventually, as these dust particles move away from the sun’s rays, they stop sinking, but they still generate enough heat to create a pocket of melt water around them. The pockets can nurture a thriving ecosystem for simple life forms.

“It’s a common phenomenon on Earth,” said co-author Phil Christensen of Arizona State University in Tempe, referring to the melting of ice from the interior. “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 has been studying ice on Mars for decades. He directs operations of a heat-sensitive camera called THEMIS (Thermal Emission Imaging System) aboard NASA’s Mars Odyssey 2001 orbiter. In previous research, Christensen and Gary Clow of the University of Colorado Boulder used modeling to demonstrate how liquid water could form in the Red Planet’s dusty snow mantle. This work, in turn, served as the basis for the new paper investigating whether photosynthesis might be possible on Mars.

In 2021, Christensen and Khuller co-authored a paper on the discovery of dusty water ice exposed in the ravines of Mars, proposing that many Martian ravines form through erosion caused by melting ice to form water liquid.

This new paper suggests that dusty ice allows enough light to pass through for photosynthesis to occur up to 9 feet (3 meters) below the surface. In this scenario, upper layers of ice prevent shallow groundwater bodies from evaporating while providing protection from harmful radiation. This is important, because unlike Earth, Mars does not have a protective magnetic field to shield it from both the sun and radioactive cosmic ray particles circulating in space.

The study authors say that the water ice most likely to form underground pools would exist in the tropics of Mars, between 30 and 60 degrees latitude, in the northern and southern hemispheres.

Khuller then hopes to recreate some of Mars’ dusty ice in a laboratory to study it up close. Meanwhile, he and other scientists are beginning to map the places on Mars most likely to search for shallow meltwater, places that could be scientific targets for possible human and robotic missions in the future.