Larissa (moon)

Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky, David J. Tholen

Larissa ( Neptune VII ) is the fünftinnerste moon of the planet Neptune.

Discovery and designation

Larissa was first discovered by astronomers Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky and David James Tholen in the evaluation of an occultation by a slight drop in brightness of the star on May 24, 1981. Since Neptune passed the star to a different time itself, it had to be a new object. Larissa was initially mistaken for a ring arc of the Adams ring. This only the third known Neptune Moon received the temporary designation S/1981 N 1 This discovery was made by the International Astronomical Union ( IAU) announced on 29 May 1981 but Larissa could not be observed since then.

At the flyby of the Voyager 2 spacecraft in the summer of 1989, photographic images were sent to Earth and confirmed Larissa only object in its orbit. The official ( re) discovery by Stephen P. Synnott was on July 28, 1989, on 2 August came the moon to the additional designation S/1989 N 2

On September 16, the moon of the IAU was named after the nymph Larissa, a daughter of the King Pelasgos and lover of Poseidon in Greek mythology, who refused to be the mistress of Zeus. She pleaded Pallas Athene for help and was transformed by it into a crow in order to escape.

The eponymous nymph is named after the eponymous city in Thessaly and the castle in the Peloponnese; the name is probably Pelasgian origin. In contrast to the moon the same asteroid was not named after the nymph, but according to the Greek city.

Web properties

Orbit

Larissa orbiting Neptune on a prograde, nearly perfectly circular orbit at an average distance of 73,548 kilometers (about 2,970 Neptune radii ) from its center, ie 48.8 thousand kilometers above the cloud tops. The orbital eccentricity is 0.001393, the orbit is inclined 0.251 degrees from the equator of Neptune.

The orbit of the next inner moon Galatea is 11.6 thousand km of Larissa's orbit removed, the next outermost moon S/2004 N 1 31,735 km. Larissa is the first moon outside of Neptune's ring system whose extreme and most conspicuous Adams ring is removed at least 10.5 thousand kilometers from the Larissa train.

Larissa goes around Neptune in about 13 hours, 18 minutes and 42.0 seconds. Since this is faster than the rotation of Neptune, as seen from Neptune Larissa goes from the west, and set in the east.

The moon moves within a critical distance, near the Roche limit, in a descending orbit around the planet and is strong tidal forces exposed. The moon will eventually be torn and train as a ring or crash or burn on the surface of Neptune.

Rotation

It is believed that Larissa synchronously rotates and its axis having an inclination of 0 °.

Physical Properties

Larissa is a dark, irregular body with dimensions of 216 × 204 × 168 km and the fourth largest of the known moons of Neptune. The average surface temperature is set at -222 ° C ( ~ 51 K ) is estimated. The surface is heavily cratered and has to have some large craters. Apparently, the moon was formed by no geological processes after its creation. It is likely that Larissa is one of the Rubble Piles that have loosely assembled from fragments of the original moons that are broken apart after Neptune 's largest moon Triton was forced by Neptune on an initially very eccentric orbit.

Research

Although the existence of Larissa was already suspected eight years before the Voyager 2 flyby, there was no Naherkundung based on the priority of a nearby Triton Passage. The probe was happening in Larissa 60,180 km distance, which was, after all the zweitnaheste flyby of a moon of Neptune.

Since the flyby of the Neptune system ground-based observations as well as the Hubble Space Telescope has been studied intensively. 2002 - 2003 the Keck Observatory observed the system by means of adaptive optics, where Larissa was again observed.

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