When NASA’s Mars Phoenix mission successfully sampled ice from the Martian arctic regions, it made astrobiological history. This sample, along with others that followed, led scientists to realize that Martian ice was buried beneath a layer of dust—although they may have overestimated how dusty it was, new findings suggest.
Using a combination of different datasets, scientists revisited the purported dustiness of Mars’s northern polar region, finding that the top layer of Martian polar ice was roughly 3% dust. This is significantly smaller than the previous estimate, 25%, an error that the researchers attribute to a calculation technique that was originally developed to study the lunar regolith. Specifically, the Martian north pole resembles an “ice-cream sandwich” with layers of dustier and older, cleaner ice that cycle throughout the seasons, the team explained in a statement. As a result, there is some variation in the amount of dust, but not as much as we believed. The findings were published in npj Space Exploration.
“We know there is water ice in the area surrounding the north pole of Mars, but there has been widespread disagreement as to how dusty that ice is,” Aditya Khuller, the study’s co-author and a planetary scientist at the University of Washington, said in the statement.
A gift from nature
Ice may be among the weirdest natural miracles in the universe. It’s a molecular lab for researchers probing physics at extreme regimes. It’s no secret that ice is one of the key signatures astronomers look for in the search for extraterrestrial life. Long cylinders of ice—ice cores—preserve information about the atmosphere from millions of years ago. Also, it keeps your drink cold in the summer.
Accordingly, studying Martian ice has led to huge advances in what we know about its “formation, evolution, and persistence, and offers insight into the broader history of Martian climate,” the team wrote in the paper. It’s also an integral part of investigating how, despite having vastly different atmospheres, Earth and Mars share some weather and geological patterns.
Small but significant
The latest study builds upon the same team’s previous work, which tested whether three common models used to analyze Martian ice held up for studying Antarctic ice on Earth. These techniques, called radiative transfer models, infer the grain radius of ice based on the albedo, or the reflectance of sunlight by a surface.
But these methods were initially devised to study soil on the Moon, Khuller said in the statement. So when the researchers found the models didn’t work that well for Earth, that raised another—arguably bigger—question: Does it really work for Mars? To find out, the team referenced an alternative method to study snow and ice and made the appropriate adaptations to account for known conditions at Mars. Then, it applied the new framework to six locations at the Martian north pole.
The researchers found that conventional models indeed overestimated the impurity of Martian ice. Specifically, dustier, darker ice forms in the winter. And of course, Mars is buffeted by huge dust storms. But dusty ice also vaporizes faster—especially during the summer—so what ends up getting exposed is cleaner, older ice, Khuller explained.
Moving the needle
Although it’s “difficult to ascertain how exactly dust is incorporated into north polar ice,” our best estimates suggest the proportion of dust is lower than we’d expect, according to the paper. Cleaner, older subsurface ice may also hint at changes in Mars’s atmospheric pressure in the past that curbed the impact of dust storms, the team added in the study.
Meanwhile, the findings—or really, any investigation of Martian ice—makes us wonder what this could all mean for life on Mars. Khuller is definitely thinking of these questions; in another paper, he and his colleagues explored whether dark layers of ice could trap sunlight and form pockets of meltwater—conditions that create rich pockets of life on Earth.
“The fact that Mars and Earth both have these similar layers of water ice and dust is interesting,” Khuller said. “Why does one planet have life and the other doesn’t?”
