These stunning images show what Martian snow looks like – it’s like nothing on Earth
The Bay Area is in the middle of a freezing cold snap, propelled by a blast of icy Arctic air.
But winter temperatures on Mars can drop more than 200 degrees. Amidst these frigidly cold conditions, the Red Planet develops ice, sleet and – at its coldest – several feet of snow.
This is not water-based snow, like what has accumulated in California’s Sierra Nevada. Because the Red Planet is so dry and so cold, scientists don’t think such snowflakes will reach the surface.
But there is another type of snow, which consists of carbon dioxide.
“Enough of a fall that you could snowshoe across,” said Sylvain Piccio, a Mars scientist at NASA’s Jet Propulsion Laboratory.
There are several reasons why this dry ice is falling from the Martian sky. First, the Red Planet has a distinct winter season – not all planets do. The planet rotates around a tilted axis, and like the Earth, the northern and southern hemispheres experience clear seasons over the course of one revolution around the sun.
This lap is about twice as long as an Earth year because Mars is farther from the Sun than we are. This means that not only does Mars receive less warmth from the Sun, but its winters are about twice as long as its winters.
“Things are really cool,” Becchio said.
During cold Martian winters, patches of carbon dioxide frost (blue, in this enhanced-color image) can form on the surface, as in this Southern Hemisphere crater.
NASA/JPL-Caltech/University of ArizonaThese freezing temperatures cause carbon dioxide and water frost to build up on the surface of the Red Planet, especially at the poles, where the coldest conditions occur. This is where scientists believe up to several feet of dry ice would fall during Martian winters.
Instead of looking like Earth’s six-sided snowflakes, Martian snowflakes will have a completely strange appearance.
“They probably look like little cubes,” Becchio explained.
This difference is due to how carbon dioxide molecules clump together when frozen. Snowflakes will also be small – smaller than the width of a human hair.
Scientists know a lot about frost and snow on Mars because of detailed measurements made by satellites orbiting the planet, which use special instruments to look at the surface.
The surface of Mars is formed by a thin layer of watery frost during the winter, as captured by Viking 2 on May 18, 1979.
NASA/JPLThe spacecraft, like the Viking lander, have also reached Earth and provided a close-up view of the icing on Mars.
“Those were incredibly beautiful pictures,” said Bicchio.
The new year on Mars began on December 26, 2022. Since the Martian year is 687 Earth days, the date changes according to the current Gregorian calendar. This also marks the beginning of spring, when the ice accumulated during the winter begins to melt. But instead of turning into a liquid, sleet, dry ice, and snow go straight to form a gas—a process known as sublimation.
When the sun shines through the transparent ice, layers near the surface can disappear first, causing pockets of gas to form. When enough pressure builds up, this carbon dioxide is released.
“You start making geysers,” Becchio said.
When carbon dioxide seeps through ice on Mars, it can release propellers of darker material (blue, in this enhanced-color image). Here, water ice also divides the Earth into polygons.
NASA/JPL-Caltech/University of ArizonaAs the Martian ice melts, the surface can also take on unique fracture patterns, such as polygons and oddly shaped spiders.
“You have nothing like it on earth,” said Becchio.
Jack Lee (he/she) is a writer for the San Francisco Chronicle. Email: jack.lee@sfchronicle.com
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