Mars may have experienced up to 20 ice ages in the past 300 to 800 million years, according to the results of a new study. Glaciers that formed during the cooling periods represent fascinating targets for future exploration missions, due to the abundance of water ice, and their potential to preserve ancient material.
In the present day, the Red Planet bears little resemblance to Earth, yet the Martian surface is dotted with evidence of large-scale weather processes that have shaped the alien landscape. One such process is the formation of huge glaciers.
During the periodic ice ages that are known to have occurred on Earth, glaciers covered vast regions of Earth’s surface. When the planet subsequently warmed, the glaciers melted, retreating to the poles. However, on Mars, the relative lack of atmosphere, and therefore heat meant that the glaciers never degraded.
Because of their longevity, these glaciers stand as a time capsule containing a record of Mars’ geological history. However, up until now scientists had been unable to deduce whether the glaciers seen on Mars today are a result of a single massive ice age, or the accumulation of multiple cooling events.
A newly published study has shed light on this question by examining high-resolution satellite footage of multiple Martian glaciers captured by the Mars Reconnaissance Orbiter (MRO). More specifically, a research team sought to analyze the distribution of boulders that are dredged up as the glacier travels outward.
If the Martian glaciers had formed during a single ice age, the team would have expected to find larger boulders embedded nearer to the source of the ice flow, getting smaller as they moved farther out. This is because, over time, rocks exposed to the surface would have been weathered by the elements, and rocks farther away from the source would have been exposed for longer by the disruptive influence of the glaciers.
MRO images of 45 glaciers were studied as part of the new study. The high-resolution data harvested by the LRO had a resolution of 25 cm (9.8 in) per pixel. The time-consuming process of analyzing the boulders embedded in the alien rivers of ice fell to Asst. Prof. Joe Levy of New York's Colgate University, and 10 of his students.
Over the course of two summers, the team identified and characterized around 60,000 glacier boulders.
Their analysis didn’t reveal the gradation of boulder sizes that would be expected from glaciers formed during a single large event. Instead, the rocks found in the rivers of ice occurred in all sizes throughout the glaciers, and seemed to be clustered together in bands stretching across the ice.
The distribution of the rocks suggests that the glaciers are comprised of multiple ice flows and sediments that occurred over the course of many ice age events. Furthermore, the presence of larger boulders far downhill could be explained if the rocks are embedded within the ice rather than being carried along the surface where they could be eroded over time.
According to the authors of the study, Mars has likely experienced 6 to 20 ice ages, that have contributed to the formation of the glaciers over the past 300 to 800 million years.
Along with providing insight on major geological features on the Martian surface, the results of the new paper could also help fill in some of the blanks surrounding the Red Planet’s orbital history, as each of the ice ages is thought to have occurred following a major shift in the orientation of the planet’s axis.
Furthermore, the glaciers represent a promising source of samples for future missions looking for evidence of past microbial life on Mars.
"These glaciers are little time capsules, capturing snapshots of what was blowing around in the Martian atmosphere," explains Levy. "Now we know that we have access to hundreds of millions of years of Martian history without having to drill down deep through the crust – we can just take a hike along the surface."
The paper has been published in the Proceedings of the National Academies of Sciences.
Source: Colgate University