For the first time, astronomers have discovered what could be an exomoon, a moon outside our solar system. The exomoon was found around the gas giant exoplanet Kepler-1625b, which orbits a star 8,000 light-years from Earth.

Although moons are common in our solar system, which has nearly 200 natural satellites, the long search for interstellar moons has been an empty one. Astronomers have had success locating exoplanets around stars outside our solar system, but exomoons are harder to pinpoint because of their smaller size.