Most of the dwarf planets now have known moons
Beyond the orbit of Neptune lies a frigid, dark, vast frontier of countless icy bodies left over from the solar system's construction 4.6 billion years ago. This region, called the Kuiper Belt, was hypothesized by astronomer Gerard Kuiper in 1951. But it took another four decades for astronomers to confirm its existence. The largest bodies are called dwarf planets, with Pluto being the biggest member. Pluto is so big, in fact, that it was discovered 60 years before other Kuiper worlds were detected. Moons around dwarf planets are elusive, though. Pluto's moon Charon wasn't found until the mid-1970s.
Now, astronomers have uncovered a moon around another dwarf planet by using the combined power of three space observatories, including archival images from the Hubble Space Telescope. Called 2007 OR10, it is the third-largest dwarf planet in the Kuiper Belt. With this moon's discovery, most of the known dwarf planets in the Kuiper Belt larger than 600 miles across have companions. These bodies provide insight into how moons formed in the young solar system. In fact, there is an emerging view that collisions between planetary bodies can result in the formation of moons. Based on moon rock samples from NASA's Apollo mission, astronomers believe that Earth's only natural satellite was born out of a collision with a Mars-sized object 4.4 billion years ago.
via Hubble - News feed