|Discovered by||Charles Kowal (1975)|
|Discovery date||September 30, 1975|
November 21, 2000 rediscovered
|S/2000 J 1|
|Adjectives||Themistoan // Themistoian //|
|Orbital characteristics |
|Mass||6.89×1014 kg|
|2.6 g/cm3 (assumed)|
Themisto was first discovered by Charles T. Kowal and Elizabeth Roemer on September 30, 1975, reported on October 3, 1975, and designated S/1975 J 1. However, not enough observations were made to establish an orbit and it was subsequently lost. (See also lost minor planet.)
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 one observed in 1975. This observation was immediately correlated with an observation on August 6, 2000, 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, which was reported to the Minor Planet Center but not published as an IAU Circular (IAUC).
Themisto's orbit is unusual: unlike most of Jupiter's moons, which orbit in distinct groups, Themisto orbits alone. The moon is located midway between the Galilean moons and the first group of prograde irregular moons, called the Himalia group.