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Raindrops on ice
When water droplets land on ice, what happens?
If the ice is at least several degrees below zero (celcius), the drops freeze quickly, and build up a whitish, bumpy surface.
When the ice surface is heated to melting, the droplets vanish into the melt.
When the ice is instead very close to zero, the droplet spreads out, but not completely. You can still see the boundary of the droplet.
In the early 90s, there was some scientific debate about the ice surface near zero. Some said it had a thin, liquid-water surface, a layer that allowed us to ice-skate and make snowballs. Others said that if that were the case, then a droplet placed on the ice would spread out and vanish. Experiments showed the droplets didn't vanish. The jury is still out on the nature of the ice surface.
-JN