Water is the essence of life.
When scientists discovered a permafrost ice cap at Mars’ north pole in 1976, the news immediately sparked speculation that life might exist on the red planet. This idea became more interesting later with the discovery of exposed ice in Antarctica.
In 2003, the Mars Odyssey orbiter, equipped with a camera capable of viewing both visible and infrared reflections from the Martian surface, discovered surprisingly large amounts of ice across Mars. These missions and others are seeking answers to one of science’s biggest questions. Was Mars a habitable world? And more importantly, does it still exist?
But water is only one part of the equation. Solar radiation is another. Radiation destroys DNA, causing mutations and cancer. For astronauts, rapid increases in solar radiation can impair the body’s ability to repair itself, even when protective shielding is in place.
“Mars lacks an effective ozone shield, allowing approximately 30% more harmful ultraviolet radiation to reach the surface compared to Earth,” Aditya Khuller and colleagues at NASA’s Jet Propulsion Laboratory wrote in a new study on the habitability of Mars.
If life were to exist on Mars, it would have to be able to withstand radiation and have access to water. Is there one potential niche that meets these requirements? Dusty ice. Ice typically emits dangerous levels of ultraviolet radiation. The new study simulated radiation and water flow and found that even a tiny amount of Martian dust inside the ice produced levels of dangerous ultraviolet radiation 25 times lower than in pure ice. The results suggest that any organisms inside this “dirty” ice shield could drink water and still be protected from radiation.
Unlike previous studies that focused on Mars’ icy polar regions, the team focused on Mars’ temperate regions. In terms of Earth, it would be a band encompassing North America, Europe, Asia, North Africa, and most of Australia in latitude, i.e. most of the areas where people currently live.
Ice, ice, baby
Mars is not exactly a vacation destination.
The thin atmosphere, made up mostly of carbon dioxide, nitrogen and argon, is far from habitable for us humans. In contrast to Earth’s blue landscape, the planet’s dusty sky is a dull red. Temperatures are very unpredictable, with highs varying between a comfortable 70 degrees Fahrenheit and an unlivable -225 degrees Fahrenheit. Extreme winds cause dust storms across the planet.
Like Earth, Mars has ice glaciers at its poles that never melt. But as summer approaches, temperate regions of the Earth warm enough to melt ice into droplets of water, creating potential nurseries for life.
This led scientists to ask: Is it possible for life to exist on Mars today?
The questions are not all academic. We have been focusing on Mars as a second home for Earthlings. Astronomers are searching for habitable planets around the galaxy, but Mars may be their best option in the short term. SpaceX famously aims to travel to Mars.
When humans first set foot on Mars, we need to know whether life already exists on Mars. As many movies have made clear, alien microbes are bad news. And we, too, may want to take steps to preserve life. One way to find out is to look at photosynthesis, the chemical reaction that sparked most of life on Earth today. On early Earth, living organisms such as bacteria, plants, and algae captured specific wavelengths of light and converted it into energy.
brighten up life
For life as we know it to exist, we need water, access to the wavelengths of light that drive photosynthesis, and protection from harmful radiation.
Dusty ice may play a role here. The ice on Mars likely began as dusty snow that eventually compressed into ice over millions of years. Some of these have turned into smaller ice floes and some have turned into glaciers. In the mid-latitudes (the “comfortable” regions), some dusty ice floes were covered with rock and later excavated by meteorite impacts, exposing the ice again.
“The polar regions of Mars are too cold for snow and ice to melt,” the authors wrote. “But the dusty ice exposed in mid-latitudes may be melting now.”
In other words, Mars may already have areas capable of harboring microorganisms.
To test the idea, the team developed a computer program to predict, based on past data, how snow on Earth and Mars would transform into ice chunks, or glaciers. The simulation took advantage of the physics of water, ice and snow and how they change when mixed with impurities such as Martian dust. The authors also developed a method to measure how Martian dust absorbs light and other radiation. They compared the Mars results with a relatively similar impure ice sheet in Greenland.
The results were clear. Compared to pure ice, ice sprinkled with Martian dust absorbed at least seven times more radiation overall and reduced levels of dangerous ultraviolet radiation. In ice, which consists of just 0.1% dust, levels of ultraviolet radiation are reduced without blocking the important wavelengths of light that support photosynthesis.
Although Mars is much colder than our home planet, Mars simulations have shown results similar to those observed under near-freezing conditions on Earth. Here, shallow ice sheets, glaciers and ice-covered lakes are teeming with microbial habitats, and layers of dark dust and sediment absorb solar radiation and heat up to form cavities in the ice. Liquid water and dust mix at the bottom of these holes, and a translucent cap of ice freezes at the top, sealing in nutrients that organisms below use for photosynthesis.
Mars’ polar ice is too cold to melt, but a mid-latitude snowpack with a bit of dust just a few inches below the ice could similarly produce enough water to sustain life and combat solar radiation. In other words, the simulated scenario is eerily similar to what we see on Earth, where conditions allow microbes to thrive.
To be clear, the results are all hypothetical. For example, water outflow on Mars depends on the size of the ice mass. How dust is distributed in Martian ice can also change melting patterns. However, this study suggests that photosynthesis may also be possible in organisms buried in Martian snow and ice.
“If small amounts of liquid water are available at these depths, mid-latitude ice exposures may be the most accessible locations to search for extant life on Mars,” the team wrote.
Image credit: Dusty icy (white) areas of Mars canyons/NASA/JPL-Caltech/University of Arizona
