The red planet has experienced between six and 20 separate ice ages over the past 300 to 800 million years, a new analysis of glaciers on Mars has revealed.
During the last ice age on Earth 20,000 years ago, our planet was covered with glaciers. Those glaciers then retreated to the poles. These masses of ice left evidence behind rocks and dumped them as they scratched and carved roads.
The Mars glaciers, on the other hand, never left. They have been frozen for more than 300 million years on the planet’s surface, which has an average temperature of negative 81 degrees Fahrenheit – they have just been covered in debris.
“All of the rocks and sand transported on the ice have remained on the surface,” study author Joe Levy, a planetary geologist and assistant professor of geology at Colgate University, said in a statement. “It’s like putting the ice in a cooler under all the sediments.”
The glaciers on Mars have long posed a mystery to geologists who have been trying to determine whether there was one extended Martian ice age that caused its formation and whether it formed during several ice ages spanning millions of years.
Studying the rocks that occur on the surface of glaciers can answer this question. Levy found that as the rocks eroded over time, the discovery of rocks that shifted from larger to smaller downward indicated one ice age.
Since it is not yet possible to visit Mars and study its surface in person, Levy and ten students at Colgate University in New York State used images from 45 glaciers taken by NASA’s Mars Reconnaissance Orbiter.
The high resolution of the images enabled the researchers to count the rocks and determine their size. The magnification of the orbits allows the team to see ‘things as big as a dining table’ on the Martian surface, Levy said.
The researchers counted and measured a total of 60,000 rocks. Artificial intelligence would have reduced some of the work, which took two summers, but AI could not distinguish rocks from the glacier surface.
“We did a kind of virtual fieldwork, walked up and down through these glaciers and mapped the rocks,” Levy said.
Instead of a steady arrangement of rocks that differ in size, the researchers observed an unexpected randomness.
“The rocks actually told us a different story,” Levy said. “It wasn’t their size that mattered; it was how they were grouped or grouped.”
The rocks actually moved inside the glaciers, rather than on the outside, so that the rocks did not erode.
But they were visible in rubble rings on the surface of the glaciers. These rings help to mark clear flow of ice formed during different ice ages.
Ice ages are caused when the tilt of the axis of a planet shifts, known as inclination, so that these different ice ages are formed separately to reflect times when Mars essentially wound on its axis.
This sheds some light on the March climate and how it has changed.
“There are really good models for Mars’ orbital parameters for the last 20 million years,” Levy said. “After that, the models tend to get chaotic.”
The team’s findings suggest that Mars experienced several ice ages.
“This paper is the first geological evidence of what Mars’ orbit and inclination have been doing for hundreds of millions of years,” Levy said. “These glaciers are small time capsules that take pictures of what was blowing around in the Martian atmosphere. Now we know we have access to hundreds of millions of years of Mars history without having to drill deep through the crust – we can only walk along the surface.”
The contents of these glaciers may contain evidence of life that once existed on Mars.
“If there are biomarkers blowing, those will also be trapped in the ice,” Levy said.
The discovery of the rock bands in the glaciers is also useful information for astronauts who may one day land on Mars and drill in the glaciers to use their water ice.
The researchers will continue to map glaciers on Mars in hopes of learning more about the planet’s past and whether there would ever be life in its history.
“There is a lot of work to be done to find out the details of the Mars climate history, including when and where it was hot enough and wet enough to be brine and liquid water,” Levy said.