Permafrost in the soil has left polygonal patterns on Mars. (NASA, JPL-Caltech, University of Arizona)
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ATLANTA — Mars may seem like a dry, desolate place, but the Red Planet transforms into an otherworldly winter wonderland, according to new video shared by NASA.
It’s late winter in Mars’ northern hemisphere, as the Perseverance rover and creative helicopter explore an ancient river delta that once fed into Jezero Crater billions of years ago.
As the main feature of the planet, it is dust that also drives the Martian weather. Dust usually heralds the arrival of winter, but the planet is no stranger to snow, ice, and sleet. At the poles of Mars, the temperature can drop to minus 190 degrees Fahrenheit.
There are two types of ice on Mars. One of them is the kind we live on Earth, made of frozen water. Thin Martian air and subzero temperatures mean that conventional snow sublimates, or goes from a solid directly into a gas, before it touches the ground on Mars.
The other type of Martian snow is carbon dioxide-based, or dry ice, and can land on the surface. A few feet of snow tends to fall on Mars in the flat areas near the poles.
“Enough fallout that you could snowshoe through it,” Sylvain Becchio, a Mars scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, said in a NASA statement. “If you’re looking to ski, you’ll have to go to a crater or a slope, where snow can build up on an inclined surface.”
So far, no orbiters or rovers have been able to see snow falling on the Red Planet because the weather phenomenon only occurs at the poles below the cloud cover at night. Cameras in orbit can’t look through the clouds, and robotic explorers that can withstand the freezing temperatures at the poles haven’t been developed.
However, the Mars Climate Sounder on the Mars Reconnaissance Orbiter can detect light that is not visible to the human eye. Carbon dioxide snow has been observed at the poles of Mars. And the Phoenix rover, which arrived at Mars in 2008, used one of its laser instruments to detect icy water ice from its location about 1,000 miles from Mars’ north pole.
Thanks to the paparazzi, we know that snowflakes on Earth are unique and six-sided. Under a microscope, Martian snowflakes probably look a little different.
“Because carbon dioxide ice has a symmetry of four, we know the dry snowflakes will be cube-shaped,” Becchio said. “Thanks to the Martian climate safer, we can say that these snowflakes will be smaller than the width of a human hair.”
Ice and carbon dioxide also form on Mars, and they can occur far from the poles. The Odyssey orbiter (which entered Mars’ orbit in 2001) watched frost form and turn into gas in sunlight, while the Viking lander spotted icy frost on Mars when it arrived in the 1970s.
At the end of winter, the season’s accumulated ice can melt and turn into gas, creating unique shapes that reminded NASA scientists of Swiss cheese, Dalmatian spots, fried eggs, spiders, and other unusual formations.
During the winter in Jezero Crater, recent highs have been around 8°F, while lows have been around 120°F.
Meanwhile, at Gale Crater in the Southern Hemisphere near the Martian equator, the Curiosity rover, which landed on Mars in 2012, experienced highs of 5 degrees Fahrenheit and lows of 105 degrees Fahrenheit.
Seasons on Mars tend to last longer because the planet’s elliptical orbit around the sun means that one Martian year is equal to 687 days, or roughly two Earth years.
NASA scientists celebrated the Martian New Year on December 26, which coincided with the arrival of the vernal equinox in the northern hemisphere.
“Scientists calculate Martian years from the planet’s northern vernal equinox that occurred in 1955 — an arbitrary starting point, but it helps to have order,” according to a post on the NASA Mars Facebook page. “Numbering Martian years helps scientists keep track of long-term observations, such as weather data collected over decades by NASA’s spacecraft.”
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