S/2003 J2 was discovered in February or March 2003 at the Mauna Kea Observatory in Hawaii by Scott S. Sheppard, David C. Jewitt, Jan T. Kleyna, Yanga R. Fernandez, and Henry H. Hsieh.
S/2003 J2 orbits Jupiter in the opposite direction from the planet's rotation. The orbit is eccentric (elliptical rather than circular) and highly inclined with respect to Jupiter's equatorial plane. All of these characteristics support the idea that S/2003 J2 is a captured asteroid, rather than having formed as part of the original Jupiter system.
This satellite has a mean radius of 1 km, assuming an albedo of 0.04. At a mean distance of about 18 million miles (28.3 million kilometers) from Jupiter, the satellite takes about 979 Earth days to complete one orbit.
S/2003 J2 was so designated because it is a satellite (S) that was discovered in 2003, and was the 2nd satellite of Jupiter (J) to be found that year.