Themisto was first discovered by Charles T. Kowal and Elizabeth Roemer on 30 September 1975, reported on 3 October 1975,[1] and designated S/1975 J 1.

[citation needed] 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.

[2] This observation was immediately correlated with an observation on 6 August 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).

[8] In October 2002 it was officially named after Themisto,[9] daughter of the river god Inachus and lover of Zeus (Jupiter) in Greek mythology.

[6] While its true albedo could not be measured by NEOWISE due to poor timing of observations,[10] it is known to have color index B−V=0.83, V−R=0.46, and V−I=0.94.