Thalassa (moon)
Voyager 2 Richard John Terrile
Thalassa ( Neptune IV ) is the second innermost moon of the planet Neptune.
Discovery and designation
Thalassa was discovered in September 1989 by Richard John Terrile on photographic images of the Voyager 2 spacecraft, probably on or shortly before 18 September. The discovery was announced on 29 September 1989; the moon got the provisional designation S/1989 N 5
On September 16, the moon of the International Astronomical Union ( IAU) was named after Thalassa, a sea goddess in Greek mythology, daughter of Aether and Hemera. Furthermore, " Thalassa ", the Greek word for " sea "; Thalassa was regarded by the ancient Greeks as the personification of the Mediterranean Sea.
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Orbit
Thalassa orbiting Neptune on a prograde, nearly perfectly circular orbit at an average distance of 50,075 kilometers (about 2,022 Neptune radii ) from its center, ie 25,311 km above the cloud tops. The orbital eccentricity is 0.0002, the orbit is inclined 0.209 degrees from the equator of Neptune.
The orbit of the innermost moon Naiad is only 1840 km of Thalassa's orbit removed, the next outermost moon Despina 2450 km. Thalassa ( and Naiad and Despina ) is in the midst of the two innermost Neptune Rings, bile - ring (1989 N3R ), which is 8100 km away from the Naiad orbit and the LeVerrier - ring (1989 N2R ) in 3130 km away, where already be the inner edge of the wide dusty Lassell ring (1989 N4R ) is located.
Thalassa orbits Neptune in about 7 hours, 28 minutes and 32.3 seconds. Since this is faster than the rotation of Neptune, as seen from Neptune Thalassa is 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 be at some point torn and train as a ring or crash or burn up in the gas layers of Neptune. In the former case, it is possible that the fragments are hurled to the path of Despina.
Rotation
It is believed that Thalassa synchronously rotates and its axis having an inclination of 0 °.
Physical Properties
Thalassa is a dark, irregularly shaped body with dimensions of 104 × 100 × 52 km, which gives the moon an unusual lenticular structure. He is the seventh largest of the known moons of Neptune. The average surface temperature is set at -222 ° C ( ~ 51 K ) is estimated. Apparently, the moon was formed by no geological processes after its creation. It is likely that Thalassa 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
Since Thalassa was only discovered during the Voyager 2 flyby, could - caused by the movement of the probe - only smeared images of Thalassa be made. 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, which Thalassa could be located and observed in image processes again.