Hubble solves puzzle of Neptune mystery moon

earthsky.org | 3/2/2019 | Paul Scott Anderson
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Click For Photo: https://en.es-static.us/upl/2019/02/Hippocamp-Neptune-HST-2019-300x180.jpg




Artist’s illustration of Neptune and its smallest known moon, Hippocamp. Image via ESA/Hubble/NASA/L. Calçada.

The origin of Neptune’s smallest known moon – Hippocamp – has been a mystery since this moon was first discovered in 2013. It orbits close to a larger Neptune moon, whose presence should have knocked Hippocamp out of orbit. That’s why astronomers have referred to it as “the moon that shouldn’t be there.” Now a new study – published February 20, 2019 in the peer-reviewed journal Nature – describes a possible solution to the mystery.

Study - Scientists - Ideas - Moon - Data

The study discusses scientists’ most recent ideas about where the moon came from, and why we still see it where we see it. Data for the study came from both the Hubble Space Telescope and the Voyager 2 spacecraft, which sped past Neptune in 1989.

Mark Showalter of the SETI Institute led the research team.

Illustration - Location - Hippocamp - Moons - Rings

Illustration of the location of Hippocamp, along with some of the other inner moons and rings of Neptune. Image via NASA/ESA/M. Showalter (SETI Institute).

Hippocamp is very tiny, only about 20 miles (34 km) in diameter. Its orbit is very close to that of Proteus, Neptune’s second-largest moon and the outermost of the planet’s inner moons. Proteus is 260 miles (418 kilometers) in diameter.

Orbits - Hippocamp - Proteus - Miles - Km

The orbits of Hippocamp and Proteus are only 7,456 miles (12,000 km) apart, which didn’t make sense, since normally it would be expected that the much larger moon would knock the much smaller one out of orbit, or the smaller one would collide with the larger one. But, apparently, that didn’t happen with Hippocamp. As noted by Showalter:

The first thing we realised was that you wouldn’t expect to find such a tiny moon right next to Neptune’s biggest inner moon. In the distant past, given the slow migration outward of the larger moon, Proteus was once where Hippocamp...
(Excerpt) Read more at: earthsky.org
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