Noora Alsaeed has usually considered constructing a snowman on Mars.
Let’s go over that once more. A snowman on Mars? That desertlike, desolate planet over there? The one coated in sand? What an uncommon daydream.
However Alsaeed is aware of a couple of issues that the remainder of us don’t. She is a planetary scientist on the College of Colorado at Boulder whose work depends on information from a NASA spacecraft that orbits Mars. She research the crimson planet’s polar areas and the peculiar molecules suspended within the ambiance above them. She is aware of that on Mars, it snows.
Similar to Earth, Mars has seasons, and throughout the winter—about twice so long as ours—icy crystals cascade from the clouds and accumulate on the frigid floor. This sounds unbelievable, on condition that Mars is notoriously dry. However Mars will get round that little technicality by substituting intricate, six-sided water snow for one thing else. The Martian ambiance, many occasions thinner than Earth’s, is primarily composed of carbon dioxide. In probably the most bitter circumstances, the carbon dioxide transforms from a gasoline into small, cube-shaped crystals of ice—particularly dry ice, the type we earthlings use to set a spooky scene on Halloween. The ice is simply too heavy to stay within the Martian sky, so it flurries down, settling in shallow piles on the crimson planet.
Mars is the planet that, other than Earth, has possible made the biggest impression on the general public creativeness. We’re effectively acquainted with Mars because the planet with all of the rovers, the place the place Elon Musk desires folks to make a second dwelling, the apparent subsequent vacation spot now that people have been to the moon. However below all that hype are subtler, downright fascinating particulars concerning the fourth planet from the solar, equivalent to its mesmerizing soundscape and its richly textured rock formations, layered like mille-feuille. Carbon-dioxide snow is only one of Mars’s many curiosities.
Scientists started to suspect that Mars’s polar areas might develop into chilly sufficient to show carbon dioxide into snow as early because the 1800s, Paul Hayne, a planetary scientist at CU Boulder who research Martian snowfall, instructed me. A NASA mission within the Seventies made observations that will later be interpreted as the primary indicators of carbon-dioxide snowfall. In 2008, a spacecraft that landed in Mars’s northern plains detected proof of snow—the water-ice variety!—falling from the ambiance. However there was no proof that the water snow truly reached the bottom; the air on Mars is so skinny that the water sublimates right into a gasoline earlier than the crystals can contact the floor.
The Mars Reconnaissance Orbiter, which has been circling Mars for greater than 15 years, has captured carbon-dioxide snow reaching the floor, although. (Scientists don’t have photographic or video proof of carbon-dioxide snowfall, solely detections made with laser expertise and observations in wavelengths which can be invisible to our eyes. “Since a lot of the snow on Mars falls within the darkness of polar night time, we have to use wavelengths of radiation outdoors of the seen spectrum,” Hayne stated.) The snow even accumulates, principally close to sloped areas equivalent to cliff sides and crater edges, Sylvain Piqueux, a analysis scientist at NASA’s Jet Propulsion Laboratory who research Mars, instructed me. He stated that sufficient of it piles as much as—hypothetically—snowshoe in.
That concept tickles the creativeness. What would possibly or not it’s like to face on the Martian floor in the midst of winter, the temperatures lastly chilly sufficient to unfastened some molecules from the sky? Snowfall happens solely throughout the chilly Martian night time, so for those who introduced some night-vision goggles, you’d see that you simply have been enveloped in a brilliant haze. Carbon-dioxide snowflakes are tiny, smaller than the width of a strand of hair—a lot smaller than their six-sided, water-ice counterparts. “It wouldn’t look as magical because it does on Earth,” Alsaeed stated.
However a Martian blizzard could be pretty in its personal approach. “It could be terribly quiet,” Hayne stated. You would possibly even be capable to catch the sound of little carbon-dioxide snow-cubes falling onto the bottom. A gust of wind might kick up “an opaque column of glittering snow,” he stated. “Glittering” and “snow”—two phrases which will reshape your psychological image of Mars.
So if astronauts might, in principle, snowshoe on the crimson planet, what else might they do? Snowboarding is probably going out, Hayne stated. “A part of what makes snowboarding potential on Earth is {that a} skinny movie of liquid water types on the surfaces of the ice particles as your ski creates friction, lubricating your movement,” he stated. On Mars, that friction would trigger icy particles to show into vapor and billow away, which “would most likely make your skis a bit squirrelly.”
The specialists don’t actually know whether or not different traditional winter actions might happen on Mars. “The concept of coping with snow that’s made from CO2 is simply so alien to me,” Alsaeed stated. “It’s gonna be a totally totally different ball sport.” Piqueux isn’t certain whether or not carbon-dioxide snow would clump sufficient to kind a snowball, not to mention a snowman; dry ice shouldn’t be precisely a chemical enigma, however how the stuff behaves below Martian circumstances is extra mysterious, he stated. On the very least, you would possibly handle a snow angel. And as for opening your mouth large to catch a cube-shaped snowflake? “You’ll be able to’t stick your tongue out on Mars, ever!” Hayne stated. (Sorry, I needed to ask!)
There’s a lot to be taught. “Snow may be a common course of for [worlds] with an environment,” Piqueux stated. “Studying the way it works would possibly inform us fairly a bit about planets—what shapes their floor, how they evolve, and what they seem like.” Scientists theorize that Mars was extra like Earth a couple of billion years in the past—heat and balmy, with actual lakes and seas. Maybe it snowed extra again then too, with chunky flakes of frozen water, and the affect of that historic precipitation stays embedded on the planet’s poles.
Many a long time in the past, effectively earlier than any area robots arrived on Mars, scientists imagined the crimson planet to be a bustling place, believing that the floor markings they noticed by means of their telescopes have been proof of clever engineering. The astronomer Percival Lowell wrote at size about these markings, which he known as canals, in The Atlantic in 1895, sparking within the public creativeness the tantalizing promise of an inhabited Mars. That ended up not being the case: Any life which will have arisen on Mars is both lengthy lifeless or hiding out of view, buried away from the glare of the solar. The dissimilarity to Earth was nearly disappointing.
However nonetheless, there are acquainted echoes, as Lowell himself acknowledged. “If astronomy teaches something, it teaches that man is however a element within the evolution of the universe, and that resemblant although numerous particulars are inevitably to be anticipated within the host of orbs round him,” he wrote. “He learns that although he’ll most likely by no means discover his double wherever, he’s destined to find any variety of cousins scattered by means of area.” Cousins like Martian snow—maybe not sufficient to make a real snowman, however definitely sufficient to stir our creativeness from thousands and thousands of miles away.
