Thirsty moon settlers might enjoy a drink with the help of the sun. At sunrise, its warmth drives water molecules from the lunar soil - ripe for harvest with the right know-how. Since 2009, several lunar probes have found evidence of abundant water, especially at the moon's poles. But no one wants the hassle of mining through the dusty surface to drink it. The moon's gravity is so low and its atmosphere so tenuous that water molecules in the ground turn directly to vapour when heated. Free to bounce around at near the speed of sound, they condense again when they get cold, piling up as frost where temperatures are low. The greatest build-up is where the sun is just rising - the dawn terminator.
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