This is what scientists imagine a moon village would look like. It would be built from the moon’s own resources: its metals, minerals and water ice. Access to water would be essential for those living on the moon. Scientists think there is frozen water trapped in craters at the moon’s south-pole but there are many unanswered questions about it. Recently, clues to the moon’s watery poles have been found far away, beyond Mars, in the asteroid belt. NASA’s Dawn spacecraft has spent several years flying through this crowded region of space. Since March 2015 it’s been orbiting the largest asteroid there, Ceres, and sending back images. This is Ceres’ northern polar region. Like the moon, its surface is pockmarked with craters. And like the moon, some areas are permanently in the shadows. Without sunlight, these dark corners are very cold, below 60 degrees Kelvin, or -200 degrees Celsius. They are some of the coldest, darkest places in the Solar System. Intriguingly, scientists have detected water ice in a few of these cold areas. You can see it here: the white spot. It took some clever image processing by the research team to pick out the ice from the surrounding dusty surface; although it’s dark, the ice reflects a tiny amount of indirect sunlight. This is not the first time that signs of water have been seen on Ceres. In March 2015, the Dawn spacecraft spotted two bright spots near the equator. They’re thought to be salt, left behind when ice turned to water vapour. At this latitude, ice doesn’t stick around for long. But in the northern craters the ice gets trapped, and that’s what makes this finding significant. Now, scientists want to understand how the ice gets to the northern craters in the first place. Ceres is thought to be one quarter frozen water, most of it just below the surface. One possibility is that this ice below the surface is ejected by huge cryovolcanos and then lands in the polar craters. This pyramid-shaped mountain was spotted earlier this year and rises 4 kilometres above the surface of Ceres, roughly half the height of Mount Everest. The ice could also come from asteroids that smash into Ceres, throwing up icy debris from the asteroids themselves or from the icy layer below the surface of Ceres. Cold, dark traps for water have now been seen on three planetary bodies: on Ceres, on the moon, and a few years ago on Mercury. This suggests that they are not one-off phenomena but general processes that can happen on any object without an atmosphere, telling scientists where to look if they want to find water on other airless bodies in our Solar System. Puzzlingly, the bright spots that tell us there’s water on Ceres have not been seen on the moon. The Lunar Reconnaissance Orbiter has detected hydrogen, a key ingredient of water, but we haven’t yet actually seen the water. Maybe it’s is mixed with frozen soil so it doesn’t reflect light in the same way as the ice on Ceres. That’s one possibility. The hope is that by understanding water ice on Ceres we could learn more about ice much closer to home, on the moon, enabling us, one day, to live there!