Meet Hippocamp: Neptune’s smallest moon has a name (and a violent past)


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A faint and frigid little moon would not must go by “Neptune XIV” anymore.

Astronomers have given a reputation — “Hippocamp” — to essentially the most just lately found moon of Neptune, which additionally previously glided by S/2004 N1. They’ve found out how large the satellite tv for pc is as effectively, and teased out some attention-grabbing particulars about its previous, a brand new research experiences.

A group led by Mark Showalter, of the SETI (Seek for Extraterrestrial Intelligence) Institute in Mountain View, California, introduced the existence of S/2004 N1 in 2013. The scientists did so after analyzing photographs taken by NASA’s Hubble Area Telescope between 2004 and 2009. [See Photos of Neptune, The Mysterious Blue Planet]

Again then, the group decided that S/2004 N1 lies about 65,400 miles (105,250 kilometers) from its mother or father planet and completes one orbit each 23 hours or so. For comparability, Earth’s personal moon — at 2,160 miles huge (three,475 km) a large in contrast with the Neptune satellite tv for pc — orbits our planet at a median distance of about 239,000 miles (384,600 km).

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And the researchers pegged S/2004 N1 because the smallest of Neptune’s 14 identified moons, estimating its diameter to be no better than 12 miles (19 km).

However issues have modified a bit since then, as the brand new research — additionally led by Showalter — experiences. The group has up to date its evaluation of the moon, after incorporating new Hubble observations made in 2016.

However let’s discuss in regards to the new identify first. “Hippocamp” is a horse-headed, fish-tailed creature in Greek mythology. The moniker, which has been accredited by the Worldwide Astronomical Union, is consistent with naming conventions for the Neptune system, which demand an affiliation with Greco-Roman mythology and the ocean. (Neptune, in fact, is the Roman god of the ocean, the equal of the Greek Poseidon.)

However Hippocampus can also be the genus identify for real-life seahorses. And Showalter is a scuba diver who loves these lovely and weird little creatures.

“So, formally, it is named after this mythological creature,” Showalter advised “However partly, in my thoughts, it is named after seahorses, as a result of I feel they’re cool.”

Within the new Hippocamp evaluation, which was printed immediately (Feb. 20) within the journal Nature, Showalter and his group employed a intelligent method they devised just a few years again (which allowed them to find the moon within the first place). The scientists “remodeled” eight sequential 5-minute Hubble exposures of the Neptune system, rearranging pixels so they might “stack” pictures of Hippocamp on prime of one another regardless of the moon’s orbital movement.

Basically, the researchers turned the eight particular person exposures right into a single 40-minute publicity.

“We got here actually near lacking it completely,” Showalter mentioned of Hippocamp. “It is too faint to see in a single Hubble [exposure].” [The Moons of Neptune Unmasked! (Infographic)]

This system is highly effective; making use of it broadly “would possibly end result within the detection of different small moons round large planets, and even planets that orbit distant stars ,” astronomer Anne Verbiscer of the College of Virginia, who was not a part of Showalter’s group, wrote in an accompanying “Information and Views” piece in the identical situation of Nature.

The brand new evaluation describes a barely bigger world than beforehand thought: Hippocamp is now believed to have a diameter of about 21 miles (34 km), the researchers report. That is about the identical measurement as Ultima Thule, the bizarre and distant object that NASA’s New Horizons spacecraft flew by on New Yr’s Day.

Hippocamp circles in the identical basic neighborhood as six moons found by NASA’s Voyager 2 spacecraft in the course of the probe’s flyby of Neptune in 1989. Hippocamp is simply 7,450 miles (12,000 km) inside to the biggest and outermost of those different six, the 260-mile-wide (420 km) Proteus.

Like Earth’s personal moon, Proteus has been slowly spiraling away from its mother or father planet for eons — and so has Hippocamp, although at a a lot slower charge. About four billion years in the past, Proteus was in all probability proper subsequent to Hippocamp and would due to this fact have devoured the smaller moon up, Showalter mentioned.

So, he and his colleagues suspect that Hippocamp is youthful than Proteus. Actually, they imagine the smaller moon was as soon as a part of its bigger neighbor: Hippocamp seemingly coalesced from items of Proteus that have been blasted into area by a long-ago comet influence, the researchers wrote within the new Nature paper.

Certainly, Hippocamp might hint its origin to the smashup that created Proteus’ large Pharos Crater. Hippocamp’s whole quantity is about 2 % of that ejected in the course of the Pharos influence. It isn’t exhausting to think about this small quantity of fabric coalescing to type a moon, Showalter mentioned.

Within the 1980s and ’90s, astronomers started to posit that the moons of the enormous planets endured quite a few comet collisions, which triggered most of the satellites to interrupt aside. The inferred origin of Hippocamp helps this view of the early photo voltaic system, mentioned Showalter, who has performed a key position within the discovery of many pure satellites over time, together with Saturn’s “ravioli moon” Pan within the early 1990s.

“That is the primary actually nice instance of a moon that bought created on account of an influence,” he mentioned.

Showalter and his group additionally used the transformation-stacking method to identify the Neptune moon Naiad, which hadn’t been seen since its discovery by Voyager 2 in 1989. And the researchers set some limits on the opportunity of discovering different moons of the ice large: Their analyses recommend there are not any moons wider than 15 miles (24 km) inside to Proteus, and none no less than 12.four miles (20 km) huge past that very same satellite tv for pc, Verbiscer famous.

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