At a distance of about 17.8 million km from Jupiter, S/2003 J12 is the innermost of the known retrograde satellites (those which orbit Jupiter in the opposite direction from the planet's rotation). It takes almost 490 Earth days to complete one orbit, and its orbit is highly inclined with respect to Jupiter's equatorial plane. S/2003 J12 is only about one kilometer across (assuming an albedo of 0.04).
S/2003 J12 was discovered between February 6 and March 7 2003 by Scott S. Sheppard and others from the University of Hawaii's Institute for Astronomy at the Mauna Kea Observatory in Hawaii.
How S/2003 J12 Got its Name:
The name "S/2003 J12" means that it is a satellite (S) that was discovered in 2003 orbiting Jupiter (J), and that it was the 12th satellite of Jupiter discovered that year. The International Astronomical Union's Planetary Nomenclature Commission has not yet given this satellite its more permanent name.