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Neptune's new moon given Greek mythological name Hippocamp

The moon was spotted by astronomers using the Hubble space telescope in 2013, and immediately prompted confusion from scientists.

Thursday 21 February 2019 14:26, UK

This is an artist's concept of the tiny moon Hippocamp that was discovered by the Hubble Space Telescope in 2013. Only 20 miles across, it may actually be a broken-off fragment from a much larger neighboring moon, Proteus, seen as a smaller crescent in the upper right. This is the first evidence for a moon being an offshoot from a comet collision with a much larger parent body. Credit: NASA, ESA and J. Olmsted (STScI)
Image: An artist's concept of Hippocamp, discovered in 2013. Pic: NASA/ESA and J Olmsted
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A tiny moon of Neptune discovered in 2013 has finally been named after scientists have finished puzzling over its origins.

It was named Hippocamp after a mythical monster from Greek mythology which has a horse's body and fish's tail, and the new moon takes the tally of Neptunian satellites to 14.

The rules of the International Astronomical Union require that the moons of Neptune are named after Greek and Roman mythology of the undersea world, so Moony McMoonface was never on the cards.

Hippocamp was spotted by astronomers using the Hubble space telescope in 2013, and immediately prompted confusion from scientists.

"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," said Mark Showalter of the SETI Institute in Mountain View, California.

Typically such a small object would have been subsumed by the gravity of the larger inner moon Proteus, but the researchers have seen that it is in a stable orbit.

The scientists believe that the tiny moon - only 20 miles (34km) across - probably began life after a comet collided with the larger moon Proteus billions of years ago.

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Diagram shows Neptune's moons. Pic: NASA/ESA and A Feild
Image: A diagram showing Neptune's moons. Pic: NASA/ESA and A Feild

Images captured by the Voyager 2 probe support this hypothesis, showing a large impact crater on Proteus - almost large enough to have shattered the large moon.

"In 1989, [when the Voyager image was taken] we thought the crater was the end of the story," said Mr Showalter.

"With Hubble, now we know that a little piece of Proteus got left behind and we see it today as Hippocamp."

The orbits of the two moons are now 7,500 miles (about 12,000km) apart.

"In the distant past, given the slow migration outward of the larger moon, Proteus was once where Hippocamp is now," said Mr Showalter.

The name and the origin of the moon will be confirmed in a paper published in the journal Nature.

It was written by astronomers from the SETI Institute and NASA.