CAPE CANAVERAL, Fla. (AP) — Neptune's newest and tiniest moon is probably an ancient piece of a much larger moon orbiting unusually close.

In the journal Nature on Wednesday, California astronomers shine a light on the 21-mile-diameter (34-kilometer-diameter) moon Hippocamp, named after the mythological sea horse.

The SETI Institute's Mark Showalter discovered Neptune's 14th moon in 2013, using Hubble Space Telescope images. Showalter and his research team theorize Hippocamp was formed from debris created billions of years ago when a comet slammed into Proteus, the largest of Neptune's inner m...