Despina (moon)
| Despina | |
|---|---|
 |
|
| Despina on an image of the Voyager 2 spacecraft | |
| Provisional or systematic name | S / 1989 N 3 |
| Central body | Neptune |
| Properties of the orbit | |
| Major semi-axis | (52,526 ± 1) km |
| Periapsis | (52,515 ± 1) km |
| Apoapsis | (52,537 ± 1) km |
| eccentricity | approx. 0.0002 |
| Orbit inclination to the equator of the central body | (0.216 ± 0.014) ° |
| Orbit inclination to the Laplace plain | 0.064 ° |
| Orbit inclination to the ecliptic | 28.56 ° |
| Orbital time | (0.33465551 ± 1⋅ 10 −8 ) d |
| Mean orbital velocity | 11.40 km / s |
| Physical Properties | |
| Albedo | 0.090 |
| Apparent brightness | 22.00 likes |
| Medium diameter | 150 ± 6 (180 × 148 × 128) km |
| Dimensions | ≈ 2.1 · 10 18 kg |
| Medium density | ≈ 1.2 g / cm 3 |
| Axis inclination | ≈ 0 ° |
| Acceleration of gravity on the surface | ≈ 0.027 m / s 2 |
| Escape speed | ≈ 64 m / s |
| Surface temperature | ≈ −222 ° C / 51 K |
| discovery | |
| Explorer | |
| Date of discovery | July 1989 |
Despina (also Neptune V ) is the third innermost moon on the planet Neptune .
Discovery and naming
Despina was discovered by Stephen Synnott around July 28, 1989 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 3 .
On September 16, the moon was named by the IAU after the nymph Despoina , a daughter of the goddess Demeter and her brother Poseidon in Greek mythology . "Despina" is based on the Greek word for "mistress, mistress" and is an epithet whose true name was only known to the initiated.
Track properties
Orbit
Despina orbits Neptune on a prograde , almost perfectly circular orbit at an average distance of 52,526 km (approx. 2,121 Neptune radii) from its center, i.e. 27,762 km above its cloud ceiling. The orbit eccentricity is 0.0002, the orbit is inclined 0.216 ° to the equator of Neptune .
The orbit of the nearest inner moon Thalassa is only 2,450 km from Despina's orbit, that of the next outer moon Galatea 9,430 km. Despina (and Naiad as well as Thalassa) is located in the middle of the two innermost Neptune rings, the Galle Ring (1989 N3R), which is 10,600 km away from Despina orbit, and the narrow LeVerrier ring (1989 N2R) only 670 km away, where the inner edge of the wide, dusty Lassell ring (1989 N4R) is already in place.
Despina orbits Neptune in around 8 hours, 1 minute and 54.2 seconds. Since this is faster than the rotation of Neptune, Despina rises in the west and sets in the east as seen from Neptune. Since the rotation time of Neptune is hardly more than twice as long at 0.6713 days, it follows that Despina needs 0.994 Neptune days for a complete apparent orbit from Neptune, i.e. almost as long as the sun . As a result, after the end of a Neptune day, it is almost in the same place in the Neptune sky as at the beginning of the day, namely a little more than two degrees further east.
Despina moves within a critical distance, near the Roche limit , in a descending orbit around the planet and is exposed to strong tidal forces. At some point it will be torn apart and form a ring or fall into the gas layers of Neptune or burn up.
rotation
It is believed that Despina rotates synchronously and that its axis is inclined by 0 °.
Physical Properties
Despina is a dark, irregular body with an extension of 180 × 148 × 128 km and thus the sixth largest of the known Neptune moons . The mean surface temperature is estimated to be −222 ° C (51 K). Apparently the moon was not shaped by any geological processes after its formation. It is likely that Despina is one of the Rubble Piles , loosely assembled from fragments of original moons that broke apart after Neptune's largest moon, Triton, was forced onto an initially very eccentric orbit.
exploration
Despina, like five other inner moons, was discovered during the Voyager 2 flyby. Low-resolution images could be made that, in contrast to those of Naiad, Thalassa and Galatea, were not smeared. Since the flyby, the Neptune system has been intensively studied through earth-based observations as well as with the Hubble space telescope . From 2002–2003 the Keck Observatory observed the system using adaptive optics , whereby Despina could be localized and observed again in image processes. In September 2009, NASA published images from 1989 that showed Despina and the shadows she cast on Neptune's cloud cover.
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: Despina description and further links (English)
- Satellite Viewer Orbit simulation of the innermost six Neptune moons
- Despina, Neptune Moon - Astronomy Picture of the Day of September 3, 2009.