Unprepossessing the hab itself may have been, but it was situated in one of the Moon’s more remarkable locations. Unlike the Earth, the Moon’s axis has no significant tilt; there are no lunar seasons. And at the Moon’s South Pole the sun never rises high in the sky. There the shadows are always long—and, in some places, permanent. Thus the pool of darkness in which Mikhail stood had been unbroken for billions of years, save by humans.

Mikhail looked down the slope, beyond the low bulges of the Station domes. On Shackleton’s floor floodlights revealed a complex tangle of quarries and lumbering machines. Down there robots toiled over the real treasure of this place: water.

When the Apollo astronauts had brought home their first dusty Moon rocks, the geologists had been dumbfounded that the samples contained not a trace of water, not even bound chemically into the mineral structures. It took some decades to unravel the truth. The Moon was no sister world of Earth but a daughter, created in the early days of the solar system when a collision with another infant world had smashed apart a proto-Earth. The debris that had eventually coalesced into the Moon had been superheated until it glowed blue-white, in the process driving off every trace of water. Later, comets had splashed on the Moon’s surface. Out of the billions of tonnes of water delivered by these lesser impacts, most had been lost immediately. But a trace, just a trace, had found its way to the permanently shadowed floors of the polar craters, a gift of water to the Moon as if in recompense for the circumstances of its birth.

By Earth’s standards the Moon’s water was little enough—not much more than a respectably sized lake—but for human colonists it was a treasure beyond price, literally worth far more than its weight in gold. It was invaluable for the scientists too, as it bore a record of eons of cometary formation, and offered indirect clues to the formation of Earth’s oceans, which had also been bequeathed by cometary impacts.