Thalassa (moon)
| Thalassa | |
|---|---|
| Provisional or systematic name | S / 1989 N 5 |
| Central body | Neptune |
| Properties of the orbit | |
| Major semi-axis | (50,075 ± 1) km |
| Periapsis | (50,065 ± 1) km |
| Apoapsis | (50,085 ± 1) km |
| eccentricity | approx. 0.0002 |
| Orbit inclination to the equator of the central body | (0.209 ± 0.02) ° |
| Orbit inclination to the Laplace plain | 0.209 ° |
| Orbit inclination to the ecliptic | 28.40 ° |
| Orbital time | (0.31148444 ± 6 · 10 −8 ) d |
| Mean orbital velocity | 11.71 km / s |
| Physical Properties | |
| Albedo | 0.091 |
| Apparent brightness | 23.32 mag |
| Medium diameter | 82 ± 6 (108 × 100 × 52) km |
| Dimensions | ≈ 3.7 · 10 17 kg |
| Medium density | ≈ 1.30 g / cm 3 |
| Axis inclination | ≈ 0 ° |
| Acceleration of gravity on the surface | 0.015 m / s 2 |
| Escape speed | 35.0 m / s |
| Surface temperature | ≈ −222 ° C / 51 K |
| discovery | |
| Explorer | |
| Date of discovery | September 1989 |
Thalassa (also Neptune IV ) is the second innermost moon on the planet Neptune .
Discovery and naming
Thalassa was discovered by Richard John Terrile in September 1989 on photographs taken by the Voyager 2 spacecraft , probably on or shortly before September 18. The discovery was announced on September 29, 1989; the moon was given the provisional designation S / 1989 N 5 .
On September 16, the moon was named by the International Astronomical Union (IAU) after Thalassa , a sea goddess from Greek mythology .
Track properties
Orbit
Thalassa orbits Neptune on a prograde , almost perfectly circular orbit at an average distance of 50,075 km (approx. 2,022 Neptune radii) from its center, i.e. 25,311 km above its cloud ceiling. The orbital eccentricity is 0.0002, the web is 0.209 ° relative to the equator of Neptune inclined .
The orbit of the innermost moon Naiad is only 1,840 km from Thalassa's orbit, that of the next outer moon Despina is 2,450 km. Thalassa (as well as Naiad and Despina) is located in the middle of the two innermost rings of Neptune, the Galle Ring (1989 N3R), which is 8,100 km from the Naiad orbit, and the LeVerrier Ring (1989 N2R) at 3,130 km, where there is already the inside edge of the wide, dusty Lassell ring (1989 N4R).
Thalassa orbits Neptune in around 7 hours, 28 minutes and 32.3 seconds. Since this is faster than the rotation of Neptune, Thalassa rises in the west and sets in the east as seen from Neptune.
The moon moves within a critical distance, near the Roche limit , in a descending orbit around the planet and is exposed to strong tidal forces. The moon will eventually be torn apart and form a ring or fall into the gas layers of Neptune or burn up. In the former case it is possible that the fragments will be thrown up to Despina's orbit.
rotation
It is believed that Thalassa rotates synchronously and that its axis has an incline of 0 °.
Physical Properties
Thalassa is a dark, irregularly shaped body with an area of 104 × 100 × 52 km that gives the moon an unusually lenticular structure. It is the seventh largest of the known Neptune moons . The mean surface temperature is estimated at −222 ° C (~ 51 K). Apparently the moon was not shaped by any geological processes after its formation. It is likely that Thalassa is one of the Rubble Piles , loosely composed of fragments of original moons that broke apart after Neptune's largest moon Triton was forced onto an initially very eccentric orbit by Neptune.
exploration
Since Thalassa was only discovered during the Voyager 2 flyby, only smeared images of Thalassa could be made - caused by the movement of the probe. Since the flyby, the Neptune system has been studied intensively by earth-based observations as well as the Hubble space telescope . From 2002–2003 the Keck Observatory observed the system using adaptive optics , whereby Thalassa could be localized and observed again in image processes.
Web links
- IAUC 4867: Neptune September 29, 1989 (discovery)
- IAUC 5347: Satellites of Saturn and Neptune September 16, 1991 (designation)
- NASA: Planetary Satellite Physical Parameters NASA: Physical Parameters (English)
- NASA: Planetary Satellite Mean Orbital Parameters NASA: Orbital Parameters (English)
- NASA: Neptunian Satellite Fact Sheet NASA: List of Parameters
- Scott S. Sheppard: Neptune's Known Satellites List with parameters of the Neptune system (English)
- USGS: Planet and Satellite Names and Discoverers Names of planets and satellites
- Polish moon page: Thalassa description and related links (English)
- Satellite Viewer Orbit simulation of the innermost six Neptune moons