Hubble solves puzzle of Neptune mystery moon (earthsky.org)

[eppur_se_muova]

By Paul Scott Anderson in Space | March 2, 2019

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.

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.
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So what is the explanation? The research team concluded that rather than being two moons that formed separately, Hippocamp is instead a “chip” knocked off of Proteus by an asteroid or comet billions of years ago. When Voyager 2 looked at Proteus with its cameras in 1989, it saw a large impact crater, which earthly astronomers call Pharos. If this scenario is correct, the rocky object that hit Proteus almost destroyed it, but instead, a smaller piece was broken off that became Hippocamp. According to Showalter:

In 1989, we thought the crater was the end of the story. With Hubble, now we know that a little piece of Proteus got left behind and we see it today as Hippocamp.

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more: https://earthsky.org/space/hubble-solves-mystery-neptune-moon-hippocamp
abstract: https://www.nature.com/articles/s41586-019-0909-9 full paper behind paywall

[procon]

1. I can just imagine how excited those scientists

we're in making that discovery. I am always in awe of the intellectual capacity for mankind to suss out even the most unlikely explanation and methodically lay out their rationale in clear and precise terms. Thanks to the Hubble's remarkable capabilities, even a non genius like me is gobsmacked that they could reach their conclusion from such a great distance.