An Neptune's Tiny Moon Hippocamp. Key Ring

An artist's concept of Neptune's tiny moon Hippocamp that was discovered by the Hubble Space Telescope in 2013. Only 20 miles across, it may actually be a broken-off fragment from a much larger neighbouring moon, Proteus, seen as a crescent in the background. This is the first evidence for a moon being an offshoot from a comet collision with a much larger parent body.