Astronomers have found plenty of Earth-like planets out there in deep space, but so far they haven't found a moon orbiting one of them. Until now, maybe. Scientists might have detected one in orbit around a planet in the constellation Sagittarius, reports Nature. If so, it's the first so-called exomoon to be spotted around an exoplanet. The catch: They made the discovery during a unique "microlensing event," and it's all but impossible to repeat the observation. (Discovery has more details on the phenomenon, in which a celestial object drifts into perfect alignment between the Earth and another more distant star, and "the space-time bending gravitational field of the closest object" brightens the light of the more distant one.)
After logging the microlensing event in June 2011 and analyzing it, astronomers believe the "closest object" could be a small star orbited by a Neptune-size planet, or a good-sized planet with its own moon. "It’s kind of a shame because we’ll probably never know what the answer is," says one astronomer not involved with the research. Still, "the exomoon evidence is tantalizing," writes Ian O'Neill at Discovery.