Proteus (moon)
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- There is also an asteroid called 9313 Protea.
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| Discovery | |
|---|---|
| Discovered by | Voyager 2 Stephen P. Synnott |
| Discovered on | ~June 16, 1989 |
| Orbital characteristics [1] | |
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| Semi-major axis | 117,647 ± 1 km (0.00079 AU) |
| Eccentricity | 0.00053 ± 0.00009 |
| Periapsis | 117,584 ± 10 km |
| Apoapsis | 117,709 ± 10 km |
| Orbital period | 1.12231477 ± 0.00000002 d |
| Orbital circumference | 739,200 km (0.005 AU) |
| Orbital velocity | max: 7.627 km/s mean: 7.623 km/s min: 7.619 km/s |
| Inclination | 0.524° (to Neptune equator) 0.026 ± 0.007° (to local Laplace plane) |
| Satellite of | Neptune |
| Physical characteristics | |
| Dimensions | 440×416×404 km (± ~15 km) [2] |
| Volume | 3.4 ± 0.3 ×107km³ [3] |
| Mass | ~4.4×1019 kg (estimate) |
| Mean density | ~1.3 g/cm³ (estimate) |
| Surface gravity | ~0.06 m/s2 (0.006 g) |
| Escape velocity | ~0.16 km/s |
| Rotation period | synchronous |
| Axial tilt | zero |
| Albedo (geometric) | 0.096 [2] |
| Surface temp. | ~51 K mean (estimate) |
| Atmosphere | none |
Proteus (proe'-tee-əs, IPA: [ˈprɔʊtiəs], Greek Πρωτέας), or Neptune VIII, is the second largest Neptunian moon, and its largest inner satellite. It is named after Proteus, the shape-changing sea god of Greek mythology.
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[edit] Discovery
Proteus was discovered from the images taken by Voyager 2 probe during the Neptune flyby in 1989. It received the temporary designation S/1989 N 1. Stephen P. Synnott and Bradford A. Smith announced (IAUC 4806) its discovery on July 7, 1989, speaking only of “17 frames taken over 21 days”, which gives a discovery date of sometime before June 16.
[edit] Physical characteristics
Proteus is more than 400 kilometres in diameter, larger than Nereid, another moon of Neptune. However, it was not discovered by Earth-based telescopes because it is so close to the planet that it is lost in the glare of reflected sunlight. Proteus is one of the darkest objects in the solar system, as dark as soot; like Saturn's moon Phoebe, it reflects only 6 percent of the sunlight that strikes it. Proteus is very cratered showing no sign of any geological modification. It is also irregularly shaped; scientists believe Proteus is about as large as a body of its density can be without being pulled into a spherical shape by its own gravity. Saturn's moon Mimas has much more regular shape despite being less massive than Proteus.
[edit] See also
[edit] External links
- IAU Circular 4806 describing the discovery of S/1989 N 1
- The Nine Planets – Proteus
- Views of the Solar System – Proteus, A Moon Of Neptune
[edit] References
- ^ R.A. Jacobson and W.M. Owen Jr. (2004). "The orbits of the inner Neptunian satellites from Voyager, Earthbased, and Hubble Space Telescope observations". Astronomical Journal 128: 1412.
- ^ a b E. Karkoschka (2003). "Sizes, shapes, and albedos of the inner satellites of Neptune". Icarus 162: 400.
- ^ P.J. Stooke (1994). "The surfaces of Larissa and Proteus". Earth, Moon ad Planets 65: 31.
| Moons of Neptune | |
|---|---|
| Naiad · Thalassa · Despina · Galatea · Larissa · Proteus · Triton · Nereid · S/2002 N 1 · S/2002 N 2 · S/2002 N 3 · Psamathe · S/2002 N 4 | |
| Neptune Trojans • Rings of Neptune |
