Cosmic Winter Olympics: Moon Skiing and Mars Skating
In 1972 during the Apollo 17 mission, astronaut Harrison Schmitt runs on the moon. Astronauts learned that in the lower gravity, a skipping motion worked well.
CREDIT: Apollo 17 Crew, NASA
The Winter Olympics may showcase the best this world has to offer when it comes to winter sports, but how would such Olympians fare off this world? The idea of ice-skating on Mars or snowboarding on Europa might seem a little farfetched, but astronauts have actually skied on the moon.
The skiing that astronauts have tried on the moon was not on snow, but on moondust.
Apollo 17 geologist Harrison "Jack" Schmitt invented a no-gear method for a kind of lunar cross-country skiing. "In the moon's low gravity," he explained to NASA, "you can ski above the moondust ? and I did. Imagine swinging your arms and legs cross-country style. With each push of your toe, your body glides forward above ground. Swing, glide, swing, glide. The only marks you leave in the moondust are the toe-pushes."
"I think downhill techniques would work very well on the moon," Schmitt added. "You even have built-in moguls, the impact craters on the slopes. Lunar gravity would allow all kinds of jumps and hops that you might find difficult on Earth."
However, unlike true snow, moondust is very abrasive, far more so than sand. While typical grains of sand on Earth have rounded edges, moondust grains have very sharp edges "and scratch anything that comes in contact with them," Schmitt said, made as they are from rocks shattered by millennia of meteor bombardment. Any skiing or sledding on the moon would require very tough equipment.
Winter Olympians on Earth only contend with normal ice, frost and snow, but on Mars there are two kinds ? frozen water, and frozen carbon dioxide, commonly known as "dry ice."
"In the winter at the poles, when it's dark all the time, it is snowing carbon dioxide as it freezes out of the atmosphere, and that sticks to a depth of 1 to 3 meters (3 to 10 ft.) and then melts away ? actually, sublimes away, goes from solid to gas ? when the sun comes up again during polar spring," said Mike Caplinger, a senior scientist at Malin Space Science Systems in San Diego. "The residual north polar cap ? the part that's left in the summer ? is exposed water ice."
Any snow on the surface of Mars made of water "is more like frost than snow," Caplinger noted. In a similar way, the carbon dioxide snow on Mars "is more like ice than snow, so I'd question if skiing is really possible. Maybe the scenes of skating along the Martian canals in Heinlein's book 'Red Planet' were a little prescient."
However, skating on Mars would face challenges. Under ideal conditions, skaters glide on the ice because of a thin layer of water their skates create by friction and pressure. However, given the cold and extraordinarily thin air of the red planet, even if the water ice and dry ice got warm enough, instead of melting, both would sublime instead.
"You wouldn't get as much purchase with skates," said research astrophysicist Scott Sandford at NASA Ames Research Center in Moffett Field, Calif. Planetary geophysicist Steve Vance at the Jet Propulsion Laboratory in Pasadena, Calif., noted that one might instead want roller skates on Martian ice, "although one would have to be careful to choose wheels that wouldn't become brittle at those cold temperatures."
And just as snowstorms on Earth can shut down skiing, "you do have big dust storms occasionally on Mars, sometimes even global ones," Sandford noted.
The Jovian moon of Europa might at first seem a great place for ice-skating since its surface is covered in ice and seems extraordinarily flat.
However, "its surface isn't shiny and reflective, which means it's not smooth, clear ice, the kind you'd want to skate on," Vance said. "Most likely, there's what you'd think of as snow on the surface, the product of the breakdown of ice from radiation and from impacts."
The surface of Europa and other icy moons "are probably not so great for ice-skating but they might be good for cross-country and other skiing events," Vance noted. Moreover, "many have naturally occurring snowboard half-pipes that stretch for hundreds of miles." On Europa, these are most likely caused by gravitational tides that are constantly squeezing Europa and changing the shape of its surface.
Given the extraordinarily tenuous atmosphere on Europa ? with an atmospheric pressure a trillionth or so that of Earth's ? "you don't have to worry about things like aerodynamic drag, so there's no need to crouch if you're going downhill, and it may be easier to steer with a different posture," Sandford said.
Still, Caplinger noted "the radiation environment on Europa is so harsh that I wouldn't want to be doing anything there, certainly not skating!" Jupiter has the largest and most powerful of all the planetary magnetospheres in the solar system, resulting in dangerous belts of radiation.
Although radiation is less of an issue on Mars, Sandford noted that one danger there is how its thin atmosphere would provide virtually no protection against any bursts of energy from the sun.
At some level, even if sports in space don't involve ice or snow or frost, "they're still winter sports in the sense that you have to equip yourself against extreme cold," Sandford said.
Sandford noted one main difference when it comes to sports in space is the weaker gravity athletes would often find. On the moon, gravity is about one-sixth Earth's; on Mars; a little more than one-third; on Europa, a little less than one-seventh.
"That means your muscles feel stronger ? you're able to jump farther, but when it comes to skiing, you'd accelerate more slowly going down the hill," Sandford said. "You'd also have to adjust how you make turns, since you're not pushing off with the same strength as on Earth. Also, it might be more difficult to change direction, since you're not held to the ground as greatly. You might want to compensate by getting more contact with the ground ? maybe bigger skis would help you turn better. Of course, there would then be competing effects ? skis would be heavier, and it'd be harder for ankles to turn."
Ski jumping would be quite different under lower gravity ? "you might need much longer ramps since there would be less acceleration," Sandford said. "Also, without the presence of any air, you'd have the competing effects of having no air resistance, making for longer jump, but also no ability to lean forward to generate aerodynamic lift, making for shorter jumps. In any event, you really don't want to fall and do a face plant and maybe crack your helmet. You wouldn't just get a zero ? you'd be dead."
To deal with any radiation, especially on Europa, "one might consider lead suits," Sandford said. The additional mass of such a suit might also "provide a muscle workout more similar to what you would get for comparable exercise on Earth," Vance added.
The spacesuits that athletes would have to wear means that a great deal of their mass would be outside their bodies, and that fact coupled with the low gravity "means that astronauts had problems moving," Vance noted. "Normal walking didn't work so well on the moon, so they did skipping motions instead, and there would likely be similar issues when it came to sports."
Snowball fights: Only on Earth
Surprisingly, snowball fights are virtually impossible anyplace else in the solar system but Earth. The reason that snowballs hold together is because snow melts slightly when squeezed here. The combination of extreme cold and weak atmospheres found elsewhere in the solar system where ice exists means that any attempts to mold a snowball might only work if you brought along a heated hydraulic press, Sandford explained. "Of course, you could always hack out a lump of ice from the surface around you and throw that, but I think it's universally understood by kids everywhere that this is extremely bad form."
Instead, any would-be athletes in space might come up with new sports one could never do here.
"There are probably lots of opportunities," Sandford said. "One can imagine that if one ever got to Pluto, or the Neptunian satellite Triton, there are a lot of nitrogen ices out there, which sublime fairly rapidly at 30 Kelvin (-405 degrees F). One could imagine wearing heated shoes to generate an explosive puff of gas whenever one's foot touched the ground for launch jumping."
Although sports in space might simply be flights of fancy, "certainly if we go out to these bodies, we have to give thought to practical issues of traveling from one place to another, and might have to give thought to how machines or people would perform to work on snow or ice," Sandford said.
"In any case, people are people ? if they hang out long enough, they'll probably compete with each other after a while," Sandford said. "When the astronauts went up in Apollo, lo and behold, they brought golf clubs. Even if you go for totally scientific reasons, people will be monkeying around. While a classic snowball fight might be impossible, I'm sure they'd think of something to do."
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