Naiad (moon)
| Naiad | |
|---|---|
 |
|
| Naiad on an image from the Voyager 2 spacecraft | |
| Provisional or systematic name | S / 1989 N 6 |
| Central body | Neptune |
| Properties of the orbit | |
| Major semi-axis | 48,227 ± 1 km |
| Periapsis | 48,208 ± 16 km |
| Apoapsis | 48,246 ± 16 km |
| eccentricity | 0.0004 ± 0.0003 |
| Orbit inclination to the equator of the central body | (4.755 ± 0.03) ° |
| Orbit inclination to the Laplace plain | (4.746 ± 0.03) ° |
| Orbit inclination to the ecliptic | 33.15 ° |
| Orbital time | (0.2943958 ± 2 · 10 −8 ) d |
| Mean orbital velocity | 11.93 km / s |
| Physical Properties | |
| Albedo | 0.072 |
| Apparent brightness | 23.91 mag |
| Medium diameter | 66 ± 6 (96 × 60 × 52) km |
| Dimensions | ≈ 1.9 · 10 17 kg |
| Medium density | ≈ 1.20 g / cm 3 |
| Axis inclination | ≈ 0 ° |
| Acceleration of gravity on the surface | ≈ 0.012 m / s 2 |
| Escape speed | ≈ 28 m / s |
| Surface temperature | ≈ −222 ° C / 51 K |
| discovery | |
| Explorer | |
| Date of discovery | September 1989 |
| Remarks | Shortest orbital time of all planetary moons. |
Naiad or Naiad (also Neptune III ) is the innermost and one of the smaller moons of the planet Neptune . At seven hours and just under four minutes, it has the shortest orbital time of a planetary moon in the solar system .
Discovery and naming
Naiad was the last Neptune moon to be discovered by Richard John Terrile while the Voyager 2 spacecraft flew past in 1989, 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 6 .
On September 16, 1991, the moon was named by the International Astronomical Union (IAU) after the Naiads ( ancient Greek for "flowing" and "flowing water"), spring and water nymphs from Greek mythology .
The name "Naiad" is the English form of the name.
Track properties
Orbit
Naiad orbits Neptune on a prograde , almost perfectly circular orbit at an average distance of 48,227 km (approx. 1,947 Neptune radii) from its center, i.e. 23,463 km above its cloud ceiling. This means that it is closer to the Neptune surface than the center of Neptune itself. The orbit eccentricity is 0.0004, the orbit is inclined 4.775 ° to the equator of Neptune , which is relatively high compared to the other five prograde regular moons within the Triton orbit .
The orbit of the nearest outer moon Thalassa is only 1,840 km from Naiad's orbit. Naiad (and Thalassa and Despina ) are located in the middle of the two innermost rings of Neptune , the Galle Ring (1989 N3R), which is 6,300 km from the Naiad orbit, and the LeVerrier Ring (1989 N2R), 4,970 km away, where there are already the inside edge of the wide, dusty Lassell ring (1989 N4R).
Naiad orbits Neptune in 7 hours, 3 minutes and 55.8 seconds. This is the shortest orbital time of all known planetary moons, it even falls short of that of Jupiter's moon Metis by 33 seconds (Metis, on the other hand, exceeds Naiad due to its proximity to Jupiter, which is 1.792 Jupiter radii). Since this is faster than the rotation of Neptune, Naiad rises in the west and sets in the east as seen from Neptune.
Naiad moves at a critical distance, near the Roche limit , in a descending orbit around the planet and will at some point be torn apart as a result of tidal forces into a ring or fall or burn up in Neptune's atmosphere.
rotation
It is believed that Naiad rotates synchronously and that its axis has an inclination of 0 °. Of all the inner moons in the solar system, Naiad is likely to have the shortest rotation period. Even shorter rotations are known from the irregular Saturn moons Hati and Mundilfari .
Physical Properties
Naiad is a very dark, irregularly shaped body measuring 96 km × 60 km × 52 km in size. It is the smallest of the inner regular Neptune moons and the eighth largest in the Neptune system, but this could possibly be surpassed by the irregular moons Halimede and Neso , discovered in 2002 , if they are darker than expected. The mean surface temperature of the Naiad 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 Naiad 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 Naiad was only discovered during the Voyager 2 flyby, only smeared pictures of Naiad 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 . In 2002–2003, the Keck Observatory observed the system using adaptive optics . Although the four largest inner moons were found, Naiad, in contrast to the nearest outer Thalassa, could not be located. Despite Hubble's ability to find all known moons and perhaps discover new ones that are even fainter than Voyager 2, Naiad was still not found. It is suspected that this is due to errors in Naiad's ephemeris .
In October 2013, the SETI institute announced the rediscovery of the moon after 24 years. The scientists were able to identify Naiad by superimposing archive images from the Hubble telescope from 2004, simulating a longer exposure time.
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: Naiad description and further links (English)
- Satellite Viewer Orbit simulation of the innermost six Neptune moons
Individual evidence
- ↑ T. Denk, S. Mottola (2013): Irregular Saturnian Moon Lightcurves from Cassini-ISS Observations: Update. DPS Conference 2013 , Denver (Colorado) , bibcode : 2013DPS .... 4540608D .
- ^ Archival Hubble Images Reveal Neptune's "Lost" Inner Moon. (No longer available online.) SETI Institute , archived from the original on October 12, 2013 ; Retrieved October 11, 2013 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
