Neptune has a new moon, and it’s also the gas giant’s smallest to date — only a little over 20 miles across. The brand new satellite is called Hippocamp.

Astronomers led by Mark Showalter of the SETI Institute discovered it using the Hubble Space Telescope combined with an innovative method to track dim and tiny objects as they orbit.

Because the object is so tiny, there’s still a lot astronomers don’t know about Hippocamp, named after a Greek sea monster in keeping with Neptune’s nautical theme. But the moon does offer some clues about its history.

Hippocamp is a chip off the block

For one, it orbits quite close to one of Neptune’s larger moons, Proteus. That, combined with its tiny size, makes astronomers think it may be a fragment of the larger moon. In fact, something like 4 billion years ago, an asteroid struck Proteus, leaving behind a crater that covers most of the moon’s surface. If Hippocamp is a product of this impact, as Showalter speculates, then it’s just a tiny piece of the total wreckage, about 2% of the total mass excavated from Proteus during the shattering collision.

Whether the moon comes from that particular impact or not, scientists still think it’s likely that Proteus and Hippocamp share a past. Like our own moon and Earth, Proteus is slowly spiraling away from Neptune due to tidal forces. Hippocamp, being so much smaller, isn’t subject to the same forces – and it’s orbiting just where Proteus used to a long time ago.