Much of the moon’s ice, which lurks beneath the surface, is found in an area 5.5° away from poles. The data suggest that the moon’s axis of rotation shifted in the past.
“It turns out these enhanced concentrations are exactly opposite each other—they’re antipodal,” says Matthew Siegler, a planetary scientist at the Planetary Science Institute who is based in Dallas, Texas. “The easiest explanation is: There used to be poles there.” Siegler and his colleagues have suggested a cause for the “polar wander”: a 3.5-billion-year-old hot spot beneath the moon’s surface. If the story holds up, it means the moon’s water is nearly as ancient as the orb itself.