It’s winter here on earth for those who live in the northern hemisphere. This means snow, rain, colder temperatures and all the other things we associate with “the holidays”. Much the same is true for Mars (aka “Earth’s twin”), which is also experiencing winter in its northern hemisphere right now. This means colder temperatures, especially around the polar regions where it can get as low as -123 °C (-190 °F), as well as ice, snow, frost and the expansion of polar ice sheets – which are made up of both water ice and frozen carbon dioxide (“dry ice”) ).
Does it snow on Mars?
While Mars does not experience snowfall in the same way that Earth does, seasonal changes result in some very interesting phenomena. Thanks to the many robotic explorers NASA and other space agencies have sent to Mars over the past 50 years, scientists have been able to see these phenomena up close. These include Viking orbiters and landers that studied the planet in the 1970s (with groundbreaking results) to the Mars Reconnaissance Orbiter (MRO), Mars Exploration Rovers (Spirit) and Opportunity), and Curiosity and Perseverance rovers exploring the surface today.
Thanks to these dedicated orbiters, landers, and rovers, scientists have learned a few salient facts about snow on Mars: it comes in two varieties (water ice and dry ice), and it only snows in the coldest areas and times—on poles, under cloud cover, and about the night. Because Mars’ atmosphere is so thin and its temperatures so extreme, water and carbon dioxide do not freeze, but sublimate, transforming from a gas directly to ice (and back again). On top of that, dry ice snowflakes are cubic, meaning they have four sides instead of the familiar six-sided configuration we’re familiar with.
As with water molecules, this is because a crystal’s shape depends on how atoms arrange themselves. In the case of CO2, molecules always bond in groups of four. Also, snow never reaches the ground on Mars, but sublimates as it falls from the clouds to the surface. Since most orbiters cannot see through these clouds, and rovers cannot withstand extreme cold, images of falling snow have never been taken. But scientists do know that Mars experiences snowfall, thanks to a handful of dedicated instruments.
These include the Mars Climate Sounder (MCS) on board MRO, which observes the Martian atmosphere in visible and infrared light to measure the temperature, humidity and dust content of the Martian atmosphere. This allows science teams to see through cloud cover and detect CO2 snow falls to the ground. Sylvain Piqueux, a planetary scientist at NASA’s Jet Propulsion Laboratory, explained the difficulties with Martian snow in a recent interview with NASA’s Mars News Report (a series dedicated to educating the public about the exploration and study of the Red Planet). As he explained:
“Fall enough that you could snowshoe over it. If you were after skiing, however, you had to enter a crater or cliff face, where snow could build up on a sloping surface. Because carbon dioxide ice has a symmetry of four, we know that dry ice snowflakes will be cube-shaped. Thanks to the Mars Climate Sounder, we can tell that these snowflakes would be smaller than the width of a human hair.”
Frost on Mars
In addition comes NASA’s Phoenix mission landed within 1,000 miles (about 1,600 kilometers) of Mars’ north pole in 2008. As part of its science operations, the lander used a laser-based atmospheric sensor — part of a special meteorological station provided by the Canadian Space Agency (CSA) — to detect water snow falling to the surface. The Viking Landers also detected water frost at their landing sites, and NASA’s Odyssey orbiter observed frost formed and sublimated at sunrise many times during the mission.
When CO2 the ice sublimates towards the end of winter, the result of the most iconic surface features on Mars. This includes the strange and beautiful shapes that scientists have called “spiders”, “Dalmatian spots”, “fried egg” and “Swiss cheese”. “Vårtine” also causes geysers to erupt when sunlight passes through layers of transparent ice and heats the pockets of gas beneath it. This triggers eruptions that send dust onto the surface, creating a feature known as “Spring Fans” that scientists are studying to learn more about the direction the Martian winds blow.
As Piqueux explained, all of this data will be crucial when it comes time to send crewed missions to Mars, which NASA hopes to do by the 2030s:
“[T]The Pheonix lander, the NASA mission that arrived on Mars in 2008, observed beautiful frost landscapes forming around it. The Pheonix lander was also able to scrape the surface and for the first time see this water ice just below the ground. This is the kind of water ice that astronauts could potentially use in the future when we go there.”
Many fascinating things accompany seasonal changes on Mars, and we are lucky to be able to witness these things thanks to many generations of robotic missions. Soon enough, astronauts will witness Mars and its dynamic climate, and their research will fuel scientific breakthroughs and discoveries for generations to come!
This article was originally published on The universe today by Matt Williams. Read the original article here.