Larissa (moon)
| Larissa | |
|---|---|
 |
|
| Larissa on a recording of the Voyager 2 spacecraft | |
| Provisional or systematic name | S / 1981 N 1, S / 1989 N 2 |
| Central body | Neptune |
| Properties of the orbit | |
| Major semi-axis | (73,548 ± 1) km |
| Periapsis | 73,445 ± 6 km |
| Apoapsis | 73,650 ± 6 km |
| eccentricity | (0.001393 ± 0.00008) |
| Orbit inclination to the equator of the central body | (0.251 ± 0.009) ° |
| Orbit inclination to the Laplace plain | 0.205 ° |
| Orbit inclination to the ecliptic | 28.63 ° |
| Orbital time | (0.55465332 ± 1 · 10 −8 ) d |
| Mean orbital velocity | 9.63 km / s |
| Physical Properties | |
| Albedo | 0.091 |
| Apparent brightness | 21.49 likes |
| Medium diameter | (194 ± 6) (216 × 204 × 168 (± ~ 10)) km |
| Dimensions | ≈ 4.20 · 10 18 kg |
| Medium density | ≈ 1.2 g / cm 3 |
| Acceleration of gravity on the surface | 0.0355 m / s 2 |
| Escape speed | 82.5 m / s |
| Surface temperature | ≈ −222 ° C / 51 K |
| discovery | |
| Explorer |
Harold J. Reitsema , |
| Date of discovery | May 24, 1981 |
Larissa (also Neptune VII ) is the fifth innermost moon on the planet Neptune .
Discovery and naming
Larissa was first discovered by the astronomers Harold J. Reitsema , William B. Hubbard , Larry A. Lebofsky and David J. Tholen when evaluating a star eclipse due to a slight decrease in brightness of the star on May 24, 1981. Since Neptune itself passed the star at a different time, it had to be a new object. Larissa was initially mistaken for an arch of the Adam's ring. This only third known Neptune moon was given the temporary designation S / 1981 N 1 . This discovery was announced by the International Astronomical Union (IAU) on May 29, 1981, but Larissa has not been observed since then.
During the flyby of the Voyager 2 spacecraft in the summer of 1989, photographs were sent to Earth and Larissa was confirmed as the only object in its orbit. The official (re) discovery by Stephen P. Synnott took place around July 28, 1989, on August 2 the moon was given the additional designation S / 1989 N 2 .
On September 16, the moon was named by the IAU after the nymph Larissa , after the Greek mythology of a daughter of King Pelasgos and lover of Poseidon .
The eponymous nymph is the namesake of the city of the same name in Thessaly and the castle on the Peloponnese peninsula ; the name is probably of Pelasgian origin. In contrast to the moon, the asteroid of the same name was not named after the nymph, but after the Greek city.
Track properties
Orbit
Larissa orbits Neptune on a prograde , almost perfectly circular orbit at an average distance of 73,548 km (approx. 2,970 Neptune radii) from its center, i.e. 48,800 km above its cloud ceiling. The orbital eccentricity is 0.001393, the web is 0.251 ° relative to the equator of Neptune inclined .
The orbit of the nearest inner moon Galatea is 11,600 km from Larissa's orbit, that of the nearest outer moon Hippocamp 31,735 km. Larissa is the first moon outside of Neptune's ring system , the outermost and most conspicuous Adams ring of which is at least 10,500 km away from Larissa's orbit.
Larissa orbits Neptune in around 13 hours, 18 minutes and 42.0 seconds. Since this is faster than the rotation of Neptune, Larissa 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. At some point the moon will be torn apart and form a ring or fall or burn up on the surface of Neptune.
rotation
It is believed that Larissa rotates synchronously and that her axis has an inclination of 0 °.
Physical Properties
Larissa is a dark, irregular body measuring 216 km × 204 km × 168 km, making it the fourth largest of the known Neptune moons . The mean surface temperature is estimated at −222 ° C (~ 51 K ). The surface is heavily cratered and has some larger craters. Apparently the moon was not shaped by any geological processes after its formation. It is likely that Larissa 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
Although the existence of Larissa was suspected eight years before the Voyager 2 flyby, there was no close-up reconnaissance due to the priority of a nearby Triton passage. The probe passed Larissa at a distance of 60,180 km, which was after all the second closest flyby to a Neptune moon.
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 , and Larissa could be observed again.
Web links
- IAUC 3608: 1981 N 1 May 29, 1981 (first discovery)
- 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: Larissa description and further links (English)
- Satellite Viewer Orbit simulation of the innermost six Neptune moons