Neptune’s smallest moon may be a chip off another moon
The tiny object has been given the official name Hippocamp
Neptune’s smallest moon may be a chunk of a neighboring moon that was knocked off by a comet.
One of seven moons that orbit closer to Neptune than the planet’s largest moon, Triton, the newly dubbed Hippocamp is just roughly 34 kilometers across, researchers report in the Feb. 21 Nature. The second-largest moon, Proteus, is Hippocamp’s nearest neighbor, orbiting about 12,000 kilometers away.
“Why would such a small moon be so close to such a big moon?” wondered astronomer Mark Showalter of the SETI Institute in Mountain View, Calif. He and his colleagues used more than a decade’s worth of observations with the Hubble Space Telescope to find the new moon, which was first reported in 2013 (SN Online: 7/16/13). Bigger moons tend to gobble up small ones as the moons form. Stranger still, the pair was probably even closer in the past, because the physics of their orbits suggests that Proteus is slowly migrating away from Neptune.