Jovian moon Europa's icy surface is pretty flat and let's say astronauts would wear ice skates attached to their spacesuits, what would ice-skating be like on Europa? Due to Europa's very low gravity (1/7.5 that of Earth) it would probably be easy to make figures in the "air" and many of them, right? Would the lack of an atmosphere change something? How would it be different from ice-skating on Earth?
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1$\begingroup$ I think it would be too cold for the ice to be slippery, but I'm not sure $\endgroup$– Steve LintonCommented Jun 8, 2020 at 16:18
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1$\begingroup$ @SteveLinton Isn't ice always slippery? $\endgroup$– LoveForChristCommented Jun 8, 2020 at 16:28
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3$\begingroup$ @LoveForChild the best source I can find quickly says that it becomes significantly less slippery below -30C. Europa rarely if ever gets above -100. Also at that temperature ice behaves like a rock -- there may be bumps, pebbles or sand lying around, so it might not be smooth on a small scale. $\endgroup$– Steve LintonCommented Jun 8, 2020 at 16:39
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3$\begingroup$ Temperatures can be too cold for ice skating. The pressure of a skate on ice causes a bit of melting, providing "lubrication" for the skate. If the cold is severe enough, the pressure will not melt the ice and you don't slip-slide-away. $\endgroup$– fred_dot_uCommented Jun 8, 2020 at 16:41
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3$\begingroup$ If it wouldn't work, write that as an answer. $\endgroup$– Organic MarbleCommented Jun 8, 2020 at 17:27
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2 Answers
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Why Is Ice Slippery? That's a surprisingly involved question. The main takeaways:
The common explanations of "pressure melting" and "frictional heating" are indeed true to some degree, but they can't fully explain why ice is as slippery as it is. In addition, they only apply relatively close to the melting point of ice, which is far from the case in the bitter -160 °C equator temperature of Europa. And in 0.134 g gravity, your weight isn't providing nearly as much pressure as on Earth.
Above -33 °C, a thin film of water starts forming on top of ice. While a great deal more can be said about this phenomenon, it suffices to note that this too is far too hot for the conditions on Europa.
When it comes to texture, ice generally also has less friction because it is very smooth, on Earth forming on top of bodies of water that are the very definition of "level".
By contrast, ice is more of a geological thing on Europa. New material is occasionally brought up from the levels below, in what is more analogue to volcanism. Ice is rock and terrain there.
From this, I can't see how skates will be any more useful than on our Moon.
"Jovian moon Europa's icy surface is pretty flat", you say, but we actually don't know that! We know that its very flat in respect to large scale features. In the relatively low resolution images and measurements we currently have, anything "ice rink-sized" wouldn't even be visible.
There's speculation, for sure, a search on the internet for what texture Europa may have will not miss the possibility of extremely non-smooth ice spikes!
Wikipedia image of ice spikes (not skating friendly) in Argentina for illustration:
Mission control will also like to note that they do not approve of "unlimited speed!", "no air resistance!" and "extremely cool figures in the air!" for meatbags on this multi-trillion expedition.
answered Jun 9, 2020 at 1:08
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1$\begingroup$ I've just asked Do predicted Penitentes on Europa only apply to snow-covered areas and not bare ice? in Earth Science SE $\endgroup$– uhohCommented Jun 9, 2020 at 3:51
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1$\begingroup$ Thank you. It's actually calming to learn that the ice on the icy moons is more like rock rather than slippery. Astronauts can walk more easy there without having to be careful not to slip, and that would be in the moons' low gravities. $\endgroup$ Commented Jun 9, 2020 at 5:06
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$\begingroup$ Guess we'll have to switch to rollerblades, then :-) $\endgroup$ Commented Jun 9, 2020 at 12:56
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$\begingroup$ Why would the astronauts actually have meatbags with them? They can't put off their suit when outside, so I guess they'd let their nutrition bags in the lander craft. $\endgroup$ Commented Jul 9, 2020 at 9:30
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To complement:
There is the highest resolution photo of Europa surface by Galileo probe. Resolution is 6 meter per pixel.
We can see the surface is no so flat, more suited for alpine skiing than ice skating. :)
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$\begingroup$ One should finally send a lander there to bring light into the dark. $\endgroup$ Commented Jun 9, 2020 at 8:34