Galatea (moon)
| Galatea | |
|---|---|
 |
|
| Galatea on an image from the Voyager 2 spacecraft | |
| Provisional or systematic name | S / 1989 N 4 |
| Central body | Neptune |
| Properties of the orbit | |
| Major semi-axis | (61,953 ± 1) km |
| Periapsis | (61,951 ± 6) km |
| Apoapsis | (61,955 ± 6) km |
| eccentricity | (0.00004 ± 0.00009) |
| Orbit inclination to the equator of the central body | (0.052 ± 0.011) ° |
| Orbit inclination to the Laplace plain | 0.062 ° |
| Orbit inclination to the ecliptic | 28.50 ° |
| Orbital time | (0.42874431 ± 1⋅ 10 −8 ) d |
| Mean orbital velocity | 10.51 km / s |
| Physical Properties | |
| Albedo | 0.079 |
| Apparent brightness | 21.85 mag |
| Medium diameter | (176 ± 8) (204 × 184 × 144 (± ~ 10)) km |
| Dimensions | (2.12 ± 0.08) 10 18 kg |
| Medium density | (0.75 ± 0.1) g / cm 3 |
| Axis inclination | ≈ 0 ° |
| Acceleration of gravity on the surface | 0.0136 to 0.0273 m / s 2 |
| Escape speed | 52.67 to 62.69 m / s |
| Surface temperature | ≈ −222 ° C / 51 K |
| discovery | |
| Explorer | |
| Date of discovery | July 1989 |
| Remarks | Resonances with Neptune's Adam's ring |
Galatea (also Neptune VI ) is the fourth innermost moon on the planet Neptune . He is responsible for the lumpy structures in Neptune's brightest ring.
Discovery and naming
Galatea was discovered on July 28, 1989 by Stephen P. Synnott on photographs taken by the Voyager 2 spacecraft . The discovery was announced on August 2, 1989 by the International Astronomical Union (IAU); the moon was given the provisional designation S / 1989 N 4 .
On September 16, the moon was named by the IAU after Galateia (from the Greek word for "the milk white"), a daughter of Nereus and Doris and one of about 50 Nereids (sea nymphs ) from Greek mythology . The Greeks often chose Galateia as the figurehead for their ships, as Galateia fled in the form of an ever-changing wave from the Cyclops Polyphemus , who wanted to marry her and, out of jealousy, killed her true love Akis with a boulder, whereupon Galateia his blood into a cold river transformed.
Track properties
Orbit
Galatea orbits Neptune on a prograde , almost perfectly circular orbit at an average distance of 61,953 km (approx. 2,502 Neptune radii) from its center, i.e. 37,189 km above its cloud ceiling. The orbital eccentricity is 0.00004, the web is 0.052 ° relative to the equator of Neptune inclined .
The orbit of the next inner moon Despina is 9,430 km from Galatea's orbit, that of the next outer moon Larissa 11,600 km. Embedded on the orbit of Galatea there is a weak, very narrow as yet unnamed ring , in which Galatea itself is possibly the source due to the impact of micrometeorites .
In addition, Galatea appears to be the first shepherd moon of the Neptune ring system , namely the brightest Adam's ring (1989 N1R), which is almost 1,000 km outside of Galatea's orbit. It is assumed that a 42:43 orbit resonance with Galatea is responsible for the unique structure of the arches. Since this moon is also responsible for the 42 radial entanglements with an amplitude of 30 km of the Adam’s ring, it was possible to determine the mass of Galatea as the only one of Neptune’s moons (with the exception of Triton ) with high accuracy.
Galatea orbits Neptune in around 10 hours, 17 minutes and 23.5 seconds. Since this is faster than the rotation of Neptune, Galatea 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 or burn up on the surface of Neptune.
rotation
It is believed that Galatea rotates synchronously and that its axis has an inclination of 0 °.
Physical Properties
Galatea is a dark, irregularly shaped body with a size of 204 × 184 × 144 km and thus the fifth 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 Galatea 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.
exploration
Since Galatea was only discovered during the Voyager 2 flyby, only smeared pictures of Galatea 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 . 2002–2003 the Keck Observatory observed the system using adaptive optics . Galatea could be observed again.
Web links
- IAUC 4824: Satellites of Neptune Aug 2, 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: Galatea description and further links (English)
- Satellite Viewer Orbit simulation of the innermost six Neptune moons