WATER IN SPACE
Dear HIW,
We’re told Mars and the Moon had water but it disappeared into space. Why do the moons around other planets, and comets, have ice, as surely it too would evaporate?
Ralph Varney in Edmonton AB
Some bodies are exposed to much less ultraviolet radiation, responsible for breaking up water molecules and freeing hydrogen and oxygen. As gas is not very dense, it’s less affected by gravity and likely to escape. Other conditions play a part, too. Dust storms are thought to have swept water molecules up into the atmosphere of Mars, where they could escape more easily.