Noora Alsaeed has typically thought of 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.
But Alsaeed is aware of a couple of issues that the remainder of us don’t. She is a planetary scientist on the University of Colorado at Boulder whose work depends on information from a NASA spacecraft that orbits Mars. She research the pink planet’s polar areas and the peculiar molecules suspended within the ambiance above them. She is aware of that on Mars, it snows.
Just like Earth, Mars has seasons, and in the course of the winter—about twice so long as ours—icy crystals cascade from the clouds and accumulate on the frigid floor. This sounds unbelievable, provided that Mars is notoriously dry. But 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 essentially the most bitter circumstances, the carbon dioxide transforms from a fuel into small, cube-shaped crystals of ice—particularly dry ice, the sort 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 pink planet.
Mars is the planet that, other than Earth, has probably 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. But beneath all that hype are subtler, downright fascinating particulars in regards to the fourth planet from the solar, akin 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 turn out to be 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, advised me. A NASA mission within the Nineteen Seventies made observations that might 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 type!—falling from the ambiance. But 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 fuel 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 know-how and observations in wavelengths which can be invisible to our eyes. “Since most of the snow on Mars falls in the darkness of polar night, we need to use wavelengths of radiation outside of the visible spectrum,” Hayne mentioned.) The snow even accumulates, largely close to sloped areas akin to cliff sides and crater edges, Sylvain Piqueux, a analysis scientist at NASA’s Jet Propulsion Laboratory who research Mars, advised me. He mentioned that sufficient of it piles as much as—hypothetically—snowshoe in.
That thought tickles the creativeness. What would possibly it’s like to face on the Martian floor in the course of winter, the temperatures lastly chilly sufficient to free some molecules from the sky? Snowfall happens solely in the course of the chilly Martian night time, so should you introduced some night-vision goggles, you’d see that you simply have been enveloped in a vivid 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 as it does on Earth,” Alsaeed mentioned.
But a Martian blizzard could be pretty in its personal method. “It would be extraordinarily quiet,” Hayne mentioned. You would possibly even be capable of 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 mentioned. “Glittering” and “snow”—two phrases that will reshape your psychological image of Mars.
So if astronauts might, in idea, snowshoe on the pink planet, what else might they do? Skiing is probably going out, Hayne mentioned. “Part of what makes skiing possible on Earth is that a thin film of liquid water forms on the surfaces of the ice particles as your ski creates friction, lubricating your motion,” he mentioned. On Mars, that friction would trigger icy particles to show into vapor and billow away, which “would probably make your skis a bit squirrelly.”
The consultants don’t actually know whether or not different basic winter actions might happen on Mars. “The idea of dealing with snow that’s made of CO2 is just so alien to me,” Alsaeed mentioned. “It’s gonna be a completely different ball game.” Piqueux isn’t positive whether or not carbon-dioxide snow would clump sufficient to kind a snowball, not to mention a snowman; dry ice will not be precisely a chemical enigma, however how the stuff behaves beneath Martian circumstances is extra mysterious, he mentioned. At the very least, you would possibly handle a snow angel. And as for opening your mouth huge to catch a cube-shaped snowflake? “You can’t stick your tongue out on Mars, ever!” Hayne mentioned. (Sorry, I needed to ask!)
There is way to be taught. “Snow might be a universal process for [worlds] with an atmosphere,” Piqueux mentioned. “Learning how it works might tell us quite a bit about planets—what shapes their surface, how they evolve, and what they look 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. Perhaps it snowed extra again then too, with chunky flakes of frozen water, and the affect of that historical precipitation stays embedded on the planet’s poles.
Many a long time in the past, effectively earlier than any house robots arrived on Mars, scientists imagined the pink planet to be a bustling place, believing that the floor markings they noticed via their telescopes have been proof of clever engineering. The astronomer Percival Lowell wrote at size about these markings, which he referred to 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 that 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.
But nonetheless, there are acquainted echoes, as Lowell himself acknowledged. “If astronomy teaches anything, it teaches that man is but a detail in the evolution of the universe, and that resemblant though diverse details are inevitably to be expected in the host of orbs around him,” he wrote. “He learns that though he will probably never find his double anywhere, he is destined to discover any number of cousins scattered through space.” Cousins like Martian snow—maybe not sufficient to make a real snowman, however actually sufficient to stir our creativeness from hundreds of thousands of miles away.