Scientists think meltwater under the Martian ice could possibly support microbial life.
Although evidence for life on Mars has never been found, suggests a new study by NASA that microbes could possibly survive under frozen water on the planet's surface.
Through computer models, the authors of the study showed that the amount of sunlight that can shine through water ice would be sufficient for photosynthesis in shallow pools of meltwater below the surface of that ice. Similar pools of water that form within ice on Earth appear to be full of life, including algae, fungi and microscopic cyanobacteria, all of which derive energy from photosynthesis.
“If we want to find life anywhere in the universe today, the Martian ice regions are probably one of the most accessible places to explore,” said principal investigator Aditya Khuller of NASA's Jet Propulsion Laboratory in Southern California.
Mars has two types of ice: frozen water and frozen carbon dioxide. In their research, published in Nature Communications Earth & Environment, Khuller and his colleagues focused on water ice. Large amounts of this formed from snow, mixed with dust, that fell on the surface during a series of Martian ice ages over the past million years. This old snow has since been converted into ice, which still contains dust particles.
Although dust particles can obscure light in the deeper ice layers, they are crucial to understanding how underground meltwater pools can form. This is because dark dust absorbs more sunlight than the surrounding ice, which can lead to warming and melting of ice up to several meters below the surface.
Meltwater as a possible source of life The white edges along gullies in Mars’ Terra Sirenum are thought to consist of dusty water ice. Scientists suspect that meltwater could form under this type of ice, providing a place for possible photosynthesis. This is reinforced by color images from NASA, although the blue hues in the images would not be visible to the human eye.
Mars scientists differ on whether ice can actually melt when exposed to the surface of Mars. This is because of the planet's thin, dry atmosphere, where water ice is likely to sublimate-right into gas, like dry ice on Earth. But the atmospheric conditions that make surface melting difficult would not apply under a dusty snow cover or glacier.
Vibrant micro-ecosystems On Earth, dust in ice can form so-called “cryoconite holes”-small cavities in ice that form when dust particles absorb sunlight and melt deeper into the ice. These dust particles eventually stop sinking, but still generate enough heat to create a meltwater pocket around them, supporting a thriving ecosystem of simple life forms.
“This is a common phenomenon on Earth,” says co-author Phil Christensen of Arizona State University. “Dense layers of snow and ice can melt from within, with sunlight penetrating and warming it like a greenhouse, rather than melting from above.”
Christensen has studied ice on Mars for decades and is leading the operations of a heat-sensitive camera called THEMIS aboard NASA's 2001 Mars Odyssey probe. In earlier research, Christensen and Gary Clow of the University of Colorado Boulder demonstrated, via models, how liquid water might form in dusty snow layers on Mars. This research formed the basis for the new study, which focuses on the possibility of photosynthesis on Mars.
In 2021, Christensen and Khuller jointly published research on dusty water ice visible in gullies on Mars. They proposed that many of these gullies arise from erosion caused by melting ice forming liquid water.
The new research suggests that dusty ice allows enough light to pass through for photosynthesis up to 3 meters below the surface. In this scenario, the upper ice layers prevent the shallow meltwater pools from evaporating, while also providing protection from harmful radiation. This is important because, unlike Earth, Mars has no protective magnetic field to shield it from both solar and cosmic rays.
According to the researchers, the water ice most likely to form underground pools would be located in the tropics of Mars, between 30 and 60 degrees latitude, in both the northern and southern hemispheres.
Khuller hopes to soon recreate Mars’ dusty ice in a laboratory to study it up close. Meanwhile, he and other scientists are beginning to map the most likely locations on Mars where shallow meltwater can be found-possibly important targets for future human and robotic missions.
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