Psamathe (moon)

Scott S. Sheppard, David C. Jewitt, January Kleyna, Matthew J. Holman John J. Kavelaars

Psamathe ( Neptune X ) is the second outermost moon of the planet Neptune. He is one of Neptune's outer retrograde irregular moons.

Discovery and designation

Psamathe was on 29 August 2003 by a team consisting of Scott S. Sheppard, David C. Jewitt Jan Kleyna and John J. Kavelaars on recordings from 4 July to 30 August 2003 and from 11 August 2001 and 14 discovered. till 16 August 2002. The recordings were made by the 8.2 -meter Subaru telescope at Mauna Kea Observatory in Hawaii. Several recordings were digitally combined until the moon is in contrast to the line-shaped stars appeared point-like. Almost simultaneously, the team led by Matthew J. Holman discovered at the 4.0 -meter Blanco telescope at the Cerro Tololo Inter- American Observatory in Chile the moon. The discovery was announced on 3 September 2003; the moon first received the provisional designation S/2003 N 1 He was until 2013 the last moon of Neptune discovered.

On 3 February 2007, the moon was then Psamathe (Greek for "sand" ), one of about 50 Nereids, sea nymphs of Greek mythology, named. They are the beautiful daughters of the wise old man Nereus, the prophecy and constant transformation have been rumored, and his wife, Doris Oceanid. Psamathe was the wife of Proteus.

Web properties

Psamathe orbits Neptune in a retrograde, highly elliptical orbit 25687000-67703000 km Distance to the center ( large semi-major axis 46.695 million km or 1885.600 Neptune radii ). The orbital eccentricity is 0.4499, the orbit is inclined 146,60 ° relative to the equator of Neptune. It is likely that by the sun, these parameters are variable due to perturbations, as the eccentricity, and even with 0.2430713 and 0.3809, the orbital inclination ( with respect to the ecliptic ) with 124.4634 and 126.312 ° and the Great semi-major axis between 46.695 49.393 million km is specified. Psamathes distance to Neptune is almost equal to the distance of the planet Mercury to the sun.

The orbit of the next inner prograde moon Laomedeia is removed an average of about 25.9 million km of Psamathes orbit, the distance of the path of the next outer retrograde Neso moon is on average only about 2.59 million km.

Since the two outermost retrograde moons Psamathe and Neso due to the similar inclinations and semi-major axes form a group, this is named after the moon erstentdeckten Neso group. They probably originated from a single asteroid that was captured by Neptune and broke. The orbits of the two moons are close to the theoretical extreme stable distance to Neptune for body with retrograde orbit. The gravitational zone of influence of a planet is defined by its Hill sphere, which in the case of Neptune about 116 million kilometers; this is the greatest of all bodies in the solar system. It is assumed that satellite orbits to 67% (corresponding to 76.3 million km ) of this range are stable.

Psamathe orbits Neptune in about 9115 days, 21 hours and 36 minutes or about 24.975 Earth years, so needed for almost as long as Saturn for its revolution around the sun. Also exist differing data from 9074.3 to 9654.93 days for the round trip time.

Physical Properties

Psamathe has a diameter of 38 km estimated, based on the assumed for them albedo of 16%. The surface is thus relatively dark. Based on this estimated Psamathe seems to be the second smallest previously known moon of Neptune. Their density is estimated to be 1.5 g/cm3. So the moon is likely to be composed predominantly of water ice.

Research

Because of the great distance to Neptune and weak brightness of 24.6 like the 1:5.250.000 is opposite to the central planet, Psamathe was not found during the flyby of Voyager 2 in 1989. Since the discovery in 2003 Psamathe could only be observed by ground-based telescopes, while their orbital elements and their brightness can be determined.