 artist's impression | |
| Discovery | |
|---|---|
| Discovered by | Charles Kowal (1975) Elizabeth Roemer (1975) |
| Discovery date | September 30, 1975 November 21, 2000 rediscovered |
| Periapsis | 5,909,000 km (0.039 AU) |
| Apoapsis | 8,874,300 km (0.059 AU) |
| Mean orbit radius | 7,391,650 km (0.04941 AU) |
| Eccentricity | 0.2006 |
| Orbital period | 129.82761 d (0.3554 a) |
| Average orbital speed | 4.098 km/s |
| Inclination | 45.81° (to the ecliptic) 47.48° (to Jupiter's equator) |
| Satellite of | Jupiter |
| Physical characteristics | |
| Mean radius | 4 km[1] |
| Circumference | ~25 km |
| Surface area | ~200 km² |
| Volume | ~270 km³ |
| Mass | 6.89 × 1014 kg |
| Mean density | 2.6 g/cm3 assumed[2] |
| Equatorial surface gravity | ~0.0029 m/s2 (0.0003 g) |
| Escape velocity | ~0.0048 km/s |
| Albedo | 0.04 assumed[1] |
| Temperature | ~124 K |
| | |
Themisto (pronounced /θɨˈmɪstoʊ/ (from Greek: Θεμιστώ), also known as Jupiter XVIII, is a small prograde irregular satellite of Jupiter. It was discovered in 1975, lost, and then rediscovered in 2000.
Discovery and naming
Themisto was first discovered by Charles T. Kowal and Elizabeth Roemer on September 30, 1975, reported on October 3, 1975[3] and designated S/1975 J 1. However, not enough observations were made to establish an orbit and it was subsequently lost. (see also Lost asteroids)
Themisto appeared as a footnote in astronomy textbooks into the 1980s. Then, in 2000, a seemingly new satellite was discovered by Scott S. Sheppard, David C. Jewitt, Yanga R. Fernández and Eugene A. Magnier, and was designated S/2000 J 1. It was soon confirmed that this was the same as the 1975 object. The Sheppard et al. announcement[4] was immediately correlated with an August 6, 2000 observation by the team of Brett J. Gladman, John J. Kavelaars, Jean-Marc Petit, Hans Scholl, Matthew J. Holman, Brian G. Marsden, Philip D. Nicholson and Joseph A. Burns — an observation that was reported to the Minor Planet Center but not published as an IAU Circular (IAUC).[5]
In October 2002 it was officially named after Themisto[6], daughter of the river god Inachus by Zeus (Jupiter) in Greek mythology.
Characteristics
Themisto's orbit is unusual. Unlike most of Jupiter's moons, which orbit in distinct groups, Themisto orbits alone, midway between the Galilean moons and the first group of prograde irregulars.
Themisto is about 8 kilometers in diameter (assuming an albedo of 0.04)[1]
0 comments:
Post a Comment