It’s winter here on Earth for those who live in the northern hemisphere. That means snow, rain, colder temperatures, and all the other things we associate with “the holiday season.” 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 they can drop to -123°C (-190°F), as well as ice, snow, frost and the expanding polar caps – which are composed of both water ice and frozen carbon dioxide (“dry ice”).
Does it snow on Mars?
Although Mars does not experience snowfall the way Earth does, seasonal changes bring about some very interesting phenomena. Thanks to the many robotic explorers that NASA and other space agencies have sent to Mars over the past 50 years, scientists have been able to observe these phenomena up close. These include the Vikings orbiters and landers that studied the planet from the 1970s (with groundbreaking results) to the Mars Reconnaissance Orbiter (MRO), the Mars Exploration Rovers (Spirit and Opportunity), and Curiosity and the Perseverance rovers exploring the surface today.
Thanks to these dedicated orbiters, landers, and rovers, scientists have learned some salient facts about snow on Mars: there are two varieties (water ice and dry ice), and it snows only in the regions and periods most cold – at the poles, under cloud cover and at night. Because Mars’ atmosphere is so thin and its temperatures so extreme, water and carbon dioxide don’t freeze but sublimate, changing directly from gas to ice (and vice versa). On top of that, dry ice snowflakes are cubic, which means they have four sides instead of the familiar six-sided configuration we know.
As with water molecules, this is because the shape of a crystal depends on how the atoms arrange themselves. In the case of CO2, the molecules always bind together in groups of four. Also, snow never reaches the ground on Mars but sublimates as it falls from clouds to the surface. Since most orbiters can’t see through these clouds, and rovers can’t withstand the extreme cold, no images of snowfall have ever 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 the 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 scan cloud cover and detect CO2 snow falling to the ground. Sylvain Piqueux, planetary research scientist at NASA’s Jet Propulsion Laboratory, explained the intricacies of Martian snow in a recent interview with NASA’s Mars News Report (a series devoted to educating the public about exploration and study of the red planet). As he explained:
“Enough falls to be able to cross on snowshoes. If you were looking to ski, however, you would have to go to a crater or cliffside, where snow could accumulate on a sloping surface. Because carbon dioxide ice has a symmetry of four, we know that dry ice snowflakes would 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
Additionally, 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 station special meteorological sensor provided by the Canadian Space Agency (CSA) — to detect icy snow falling on the surface. The viking Landers have also detected frost at their landing sites, and NASA’s Odyssey orbiter has observed the formation and sublimation of frost at sunrise several times during its mission.
When the CO2 the ice sublimes towards the end of winter, resulting in the most iconic surface features of Mars. This includes the weird and beautiful shapes that scientists have dubbed “spiders”, “Dalmatian spots”, “fried eggs” and “Swiss cheese”. The “spring thaw” also causes geysers to erupt when sunlight passes through layers of translucent ice, heating the gas pockets below. This triggers eruptions that send dust to the surface, creating a feature known as “Spring Fans” that scientists are studying to learn more about which direction Martian winds are blowing.
As Piqueux explained, all of this data will be vital when it comes time to send manned 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 that formed 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 get there.
Many fascinating things come with seasonal changes on Mars, and we are fortunate to witness them through many generations of robotic missions. Soon, astronauts will witness Mars and its dynamic climate first-hand, and their research will fuel scientific breakthroughs and discoveries for generations to come!
This article was originally published on Universe today by Matt Williams. Read the original article here.