S/2003 J12 was discovered between Feb. 6 and Mar. 7, 2003 by Scott S. Sheppard and others from the University of Hawaii's Institute for Astronomy at the Mauna Kea Observatory in Hawaii.
At a distance of about 11 million miles (17.8 million kilometers) 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 less than a mile across ( about one kilometer), assuming an albedo of 0.04).
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.