Mars has long been theorized to be a place where ancient microbial life once existed, and NASA and other agencies have sent countless missions to the planet in hopes of uncovering the mystery that is life on Mars. While evidence for this microbial life is yet to have been found, a new NASA study from a group of scientists proposes that these microbes can survive beneath frozen water ice on the Martian surface.
More specifically, the team suggests that the amount of sunlight that would shine through the water ice and into shallow pools under the ice would be enough for any microbes to perform photosynthesis. The team utilized computer modeling to make their proposal, and pools of water similar to these Martian pools have been found on Earth to contain algae, fungi, and microscopic cyanobacteria — all of which perform 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 be looking,” said lead author Aditya Khuller of NASA’s Jet Propulsion Laboratory (JPL).
Image of Martian surface gullies in the Terra Sirenum region. The white edges along the gullies are believed to be dusty water ice. (Credit: NASA/JPL-Caltech/University of Arizona)
Interestingly, Mars has been found to feature two different types of ice — water ice and frozen carbon dioxide — with Khuller et al. specifically focusing on water ice in their study. The large amounts of water ice found on Mars’ surface likely formed during a series of Martian ice ages that occurred in the last few million years, during which snow mixed with dust and ultimately solidified into ice.
When the snow froze into ice, the dust particles mixed into it froze as well. These dust particles can obscure some of the light shining through the ice into the water pools, which is key to understanding how the subsurface water pools can form. The darker dust frozen within the ice absorbs more sunlight than the ice surrounding it, causing the ice to warm up and melt just a few feet below the surface, creating subsurface water pools.
However, planetary scientists are still unsure whether water ice can melt on the Martian surface due to water ice sublimating (turning directly into gas) in Mars’ thin and dry atmosphere. Scientists aren’t sure if these atmospheric effects would affect surface water ice and believe that they wouldn’t apply to ice located beneath the Martian surface.
So what exactly are these subsurface water pools, and how do they foster thriving ecosystems of microbes and other living organisms?
On Earth, dust located within water ice can create cryoconite holes — small ice cavities that form when windblown dust (cryoconite) lands within the ice, absorbs sunlight, and melts further and further into the ice. Eventually, the cryoconite will sink far enough into the ice that the Sun’s rays won’t warm it enough to continue sinking but will warm it just enough to continue melting the ice around it, creating a small pocket of melted water. Within these pockets of water, ecosystems can form and support simple lifeforms.
Cryoconite holes found within the Matanuska Glacier in Alaska in 2012. Small pockets of water ultimately form from these small holes. (Credit: Kimberly Casey)
“This is a common phenomenon on Earth. 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,” said co-author Phil Christensen of Arizona State University.
Khuller et al.’s new paper suggests that the dusty water ice allows just enough sunlight to shine through for photosynthesis to occur. The team found that in some situations, photosynthesis can occur up to three meters below the surface. This is due to the upper ice layers preventing the evaporation of shallow subsurface pools and protecting the pools from harmful radiation from the Sun. Mars lacks a strong magnetic field like Earth’s, meaning harmful radiation from the Sun and radioactive cosmic ray particles from space can easily penetrate the atmosphere and reach the surface.
Past research from Christensen has shown that liquid water can form within the dusty snowpack on Mars. A 2021 paper from Christensen and Khuller presented the discovery of exposed dusty water ice in Martian gullies and proposed that Martian gullies form by erosion caused by melting ice. These two studies helped lay the foundation of Khuller et al.’s latest paper in determining whether or not photosynthesis is possible on Mars.
Another Martian gully, found within the Dao Vallis region of Mars. The white material within the gully is likely dusty water ice. (Credit: NASA/JPL-Caltech/University of Arizona)
Khuller et al. believe that the dusty water ice that’s needed to form these subsurface pools would exist in Mars’ tropics region in both of the planet’s northern and southern hemispheres. Next, the team plans to recreate the dusty Martian water ice in laboratories on Earth and map out where the shallow water pools could exist on Mars. Knowing where these pools exist could allow for the creation of new landing targets for future surface missions — both robotic and human.
Khuller et al.’s study was published in Nature Communications Earth & Environment on Oct. 17.
(Lead image: Mars and its thin atmosphere as seen by the Hope spacecraft. Credit: UAESA/MBRSC/HopeMarsMission/EXI/AndreaLuck)