Proteus (moon)
| Proteus | |
|---|---|
.jpg) |
|
| Proteus on an image of the Voyager 2 spacecraft | |
| Provisional or systematic name | S / 1989 N 1 |
| Central body | Neptune |
| Properties of the orbit | |
| Major semi-axis | (117,647 ± 1) km |
| Periapsis | (117,584 ± 10) km |
| Apoapsis | (117,709 ± 10) km |
| eccentricity | (0.00053 ± 0.00009) |
| Orbit inclination to the equator of the central body | 0.524 ° |
| Orbit inclination to the Laplace plain | (0.026 ± 0.007 °) ° |
| Orbit inclination to the ecliptic | 28.92 ° |
| Orbital time | (1.12231477 ± 2 · 10 −8 ) d |
| Mean orbital velocity | 7.623 km / s |
| Physical Properties | |
| Albedo | 0.096 |
| Apparent brightness | 19.75 likes |
| Medium diameter | 420 ± 7 (436 × 416 × 404 (± ~ 15)) km |
| Dimensions | ≈ 5.0 · 10 19 kg |
| Medium density | ≈ 1.3 g / cm 3 |
| Sidereal rotation | (1.12231477 ± 2 · 10 −8 ) |
| Axis inclination | 0 ° |
| Acceleration of gravity on the surface | 0.075 m / s 2 |
| Escape speed | 180 m / s |
| Surface temperature | ≈ −222 ° C / 51 K |
| discovery | |
| Explorer |
Voyager 2 |
| Date of discovery | June 1989 |
| Remarks | Considered the largest non-spherical natural satellite |
Proteus (also Neptune VIII ) is the seventh innermost and second largest moon on the planet Neptune . It is considered to be the largest non-spherical natural satellite of any planet in the solar system .
Discovery and naming
Proteus was discovered around June 16, 1989 by Stephen P. Synnott and Bradford A. Smith in images of the Voyager 2 spacecraft that passed through Proteus in August 1989. The new discovery was announced on July 7, 1989 by the International Astronomical Union (IAU); the moon was given the provisional designation S / 1989 N 1 .
Although Proteus is the second largest Neptune moon and therefore larger than the Nereid , it was not discovered from Earth. As it moves very close to Neptune, it is outshone by its reflected sunlight. That is why it was only discovered 40 years after Nereid and 143 years after Triton .
On September 16 the moon was named by the IAU after Proteus (the "old man from the sea"), a sea god from Greek mythology .
Track properties
Orbit
Proteus orbits Neptune on a prograde , almost perfectly circular orbit at an average distance of 117,647 km (approx. 4,751 Neptune radii) from its center, that is, 92,900 km above its cloud ceiling. The orbital eccentricity is 0.00053, the web is 0.524 ° relative to the equator of Neptune inclined .
The orbit of the closest inner moon Hippocamp is 12,364 km from Proteus' orbit, that of the next outer moon Triton is at 237,100 km more than five times the distance.
Proteus orbits Neptune in 26 hours, 56 minutes and 8.0 seconds.
rotation
The rotation time is the same as the orbital time and Proteus, like the Earth's moon , shows a synchronous rotation .
Physical Properties
Proteus is an irregularly shaped body with dimensions of 436 km × 416 km × 404 km. Many scientists believe that Proteus has the maximum size of a non-round body in relation to its density . It is just big enough that its own gravity does not yet force it into a spherical shape. The slightly smaller Saturn moon Mimas has a rounder shape, although it has a little less mass than Proteus, which may be due to the slightly lower density and higher temperature of Mimas. The somewhat larger Saturn moon Enceladus has more mass and a higher density and, like the equally large Uranus moon Miranda , is more spherical than Proteus.
Proteus has a dark surface with an albedo of 0.096, which means that only ten percent of the incident sunlight is reflected . This makes it one of the darkest large to medium-sized moons in the solar system. The total area is 550,000 km 2 , which roughly corresponds to the area of metropolitan France . The mean surface temperature is estimated at −222 ° C (≈51 K ).
Its surface is heavily cratered and, in addition to some larger craters, also has linear, trench-like structures. The largest crater, which spans about half the diameter of the moon, was named Pharos . Apparently the moon was not shaped by any geological processes after its formation.
exploration
Although close-up reconnaissance was not possible during the Voyager 2 flyby due to the priority of a nearby Triton passage, Proteus was able to pass at a distance of 97,860 km and images were taken with a resolution of up to 1.35 km / pixel. Proteus was big enough and discovered early enough that it was the only one of the six Neptune moons newly discovered by the probe that could still be included in the observation program. In order to avoid smearing the images due to the movement of the probe , they were produced in only six gray levels due to the reduction in the amount of data.
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 , and Proteus could be observed again.
Web links
- IAUC 4806: 1989 N 1 July 7, 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
- Proteus with Bill Arnett on The Nine Planets
- Proteus, A Moon Of Neptune on Views of the Solar System
- Ted Stryk: Page about Proteus (English)
- Polish moon page: Proteus description and further links (English)
- Satellite Viewer Orbit simulation of the innermost six Neptune moons