New Moon Discovered Orbiting Around Neptune

Scientists reveal Neptune's tiny new moon, Hippocamp

Scientists reveal Neptune's tiny new moon, Hippocamp

While there are three Hubble programmes dedicated to studying Neptune's rings, arcs and small inner moons, the study's authors had to develop their own specialised image processing techniques to focus on the inner satellites, including Hippocamp, because of their speedy orbits.

"The first thing we realized 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.

The orbits of the two moons are now about 12,070 kilometres apart.

Until recently, Neptune's newly found moon was named S/2004 N1 (S for satellite, 2004 from the year the astronomers sighted the moon for the first time, and N from Neptune). Its new name is Hippocamp. Showalter is an avid scuba diver who enjoys watching seahorses in their native habitat, so he was naturally "delighted" when the IAU approved his recommendation. It's only about 21 miles in diameter; by comparison, Neptune is 30,599 miles in diameter.

The moon is so tiny and dim that most images of the Neptune system don't reveal it at all. They have also concluded that based on its orbit, it was once much closer to Neptune's much larger moon Proteus, which has been slowly spiraling away from its host planet.

Neptune, named after the Roman god of the sea, is the third most massive planet by after Jupiter and Saturn. What's more, in addition to the long distance and the small size of the object, the astronomers were challenged by the moon's rapid orbital speed, which made it hard to combine multiple images and prevent smearing. "In 1989, we thought the crater was the end of the story", said Showalter. The debris from shattered moons re-coalesced into the second generation of natural satellites that we see today. But it showed up when Showalter and his colleagues stacked a sequence of images on top of each other.

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"There is a lot each of these systems can tell us that we don't know because we haven't had the opportunity to visit and stay long enough to see it", she said. And when we did that this extra dot showed up.

Showalter was "elated" when the image appeared, but there was still plenty of work to do. Mark Showalter of the SETI Institute discovered Hippocamp in July 2013 when analysing over 150 archival images of Neptune taken by Hubble from 2004 to 2009.

According to the researchers, Hippocamp's size and orbital placement suggest that it may be an ancient fragment of Proteus. This makes Hippocamp the seventh inner moon found around Neptune, bringing the planet's total moons to 14. Given the amount of debris in that region of the solar system, Showalter estimates that a body the size of Hippocamp would have been struck by a large impactor something like nine times in the past 4 billion years, with each strike breaking the tiny moon apart and leaving it to reform.

And in fact, Proteus has a very big crater, which suggests it experienced a significant impact at some point in its history.

Above you'll see the relative sizes of the various moons of Neptune as calculated and processed by Ted Stryk. The moniker, which has been approved by the International Astronomical Union, is in keeping with naming conventions for the Neptune system, which demand an association with Greco-Roman mythology and the sea.

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