NASA images showcase eerie beauty of winter on Mars

By Ashley Strickland, CNN

Mars may seem like a dry, desolate place, but the red planet transforms into an otherworldly wonderland in winter, according to a new video shared by NASA.

It’s late winter in Mars’ Northern Hemisphere, where the Perseverance rover and Ingenuity helicopter are exploring an ancient river delta that once fed into Jezero Crater billions of years ago.

As the planet’s main feature, dust also drives Martian weather. Dust usually heralds winter’s arrival, but the planet is no stranger to snow, ice and frost. At the Martian poles, the temperature can dip as low as minus 190 degrees Fahrenheit (minus 123 degrees Celsius).

There are two types of snow on Mars. One is the kind we experience on Earth, made of frozen water. The thin Martian air and subzero temperatures mean that traditional snow sublimates, or transitions from a solid directly to a gas, before touching the ground on Mars.

The other type of Martian snow is carbon dioxide-based, or dry ice, and it can land on the surface. A few feet of snow tend to fall on Mars in its flat regions near the poles.

“Enough falls that you could snowshoe across it,” said Sylvain Piqueux, a Mars scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, in a statement from a NASA release. “If you were looking for skiing, though, you’d have to go into a crater or cliffside, where snow could build up on a sloped surface.”

So far, no orbiters or rovers have been able to see snow fall on the red planet because the weather phenomenon only occurs at the poles beneath cloud cover at night. The cameras on the orbiters can’t peer through the clouds, and no robotic explorers have been developed that could survive the freezing temperatures at the poles.

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However, the Mars Climate Sounder instrument on the Mars Reconnaissance Orbiter can detect light that’s invisible to the human eye. It has made detections of carbon dioxide snow falling at the Martian poles. The Phoenix lander, which arrived on Mars in 2008, also used one of its laser instruments to detect water-ice snow from its spot about 1,000 miles (1,609 kilometers) away from the Martian north pole.

Thanks to photographers, we know snowflakes on Earth are unique and six-sided. Beneath a microscope, Martian snowflakes would likely look a little different.

“Because carbon dioxide ice has a symmetry of four, we know dry-ice snowflakes would be cube-shaped,” Piqueux said. “Thanks to the Mars Climate Sounder, we can tell these snowflakes would be smaller than the width of a human hair.”

Ice and carbon dioxide-based frosts also form on Mars, and they can occur farther away from the poles. The Odyssey orbiter (which entered Mars’ orbit in 2001) has watched frost forming and turning to a gas in the sunlight, while the Viking landers spotted icy frost on Mars when they arrived in the 1970s.

At the end of winter, the season’s buildup of ice can thaw and turn into gas, creating unique shapes that have reminded NASA scientists of Swiss cheese, Dalmatian spots, fried eggs, spiders and other unusual formations.

During winter in Jezero Crater, recent high temperatures have been about 8 F (minus 13 C), while lows been about minus 120 F (minus 84 C).

Meanwhile, at Gale Crater in the Southern Hemisphere near the Martian equator, the Curiosity rover, which landed on Mars in 2012, has been experiencing highs of 5 F (minus 15 C) and lows of minus 105 F (minus 76 C).

Seasons on Mars tend to last longer because the planet’s oval-shaped orbit around the sun means that a single Martian year is 687 days, or nearly two Earth years.

NASA scientists celebrated the Mars new year on December 26, which coincided with the arrival of the spring equinox in the Northern Hemisphere.

“Scientists count Mars years starting from the planet’s northern spring equinox that occurred in 1955 — an arbitrary point to begin, but it’s useful to have a system,” according to a post on the NASA Mars Facebook page. “Numbering Mars years helps scientists keep track of long term observations, like weather data collected by NASA spacecraft over the decades.”

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