Themisto (moon)

Themisto or , is a small prograde non-spherical moon of Jupiter. It was found in 1975, lost, and then refound in 2000.

 Discovery and naming 

Themisto was first found by Charles T. Kowal and Elizabeth Roemer on September 30, 1975, reported on October 3, 1975IAUC 2845: Probable New Satellite of Jupiter 1975 October 3 (discovery) and designated . However, not enough observations were made to establish an orbit and it was subsequently lost.

Themisto appeared as a footnote in astronomy textbooks into the 1980s. Then, in 2000, a seemingly new moon was found by Scott S. Sheppard, David C. Jewitt, Yanga R. Fernández and Eugene A. Magnier, and was designated . It was soon confirmed that this was the same as the 1975 object. The Sheppard et al. announcementIAUC 7525: S/1975 J 1 = S/2000 J 1 2000 November 25 (recovery) 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).MPEC 2000-Y16: S/1975 J 1 = S/2000 J 1, S/1999 J 1 2000 December 19 (recovery and ephemeris)

In October 2002 it was officially named after Themisto,IAUC 7998: Satellites of Jupiter 2002 October 22 (naming the moon) 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 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)

 References 

 Ephemeris IAU-MPC NSES
 Mean orbital parameters NASA JPL

 Other websites 
 David Jewitt's pages
 Scott Sheppard's pages

Category:Jupiter's moons