May 24, 2082, Neptune’s moon Triton: The hero of one of my novels, Nick, tries to move a block of ice weighing 80 kg (176 lbs). But it’s damn hard, even with Triton’s low force of gravity. “On Earth, the ice would slide because its bottom would melt due to the pressure, like under the blade of a skate, but it’s too cold for that here,” Nick thinks. A mistake, a Swedish reader just wrote to me. The idea that ice skating works because ice melts under pressure and then forms a lubricating layer is old. Ice does in…