The moon of Jupiter – S/2003 J17 – was discovered in April 2003 by B. Gladman. This discovery was achieved by the 3.6-m Canada-France-Hawaii telescope atop Mauna Kea (Hawaii). You can read additional details in The International Astronomical Union Circular (→IAU).
    S/2003 J17 is one of six new satellites discovered since the →Voyager-2 Jupiter system fly-by which occured 24 years ago (1979). With this moon, the astronomer discovered also: Cyllene, Kore, S/2003 J15, S/2003 J16 and S/2003 J18. 
    The moon is in elliptical retrograde orbit (→eccentricity e = 0.2381) with a →semimajor axis a = 22,983,000 km. At pericenter (closest to the planet) S/2003 J17 is separated from the Jupiter a distance of q = 17,510,748 km. At apocenter (furthest from the planet) this moon is separated from the Jupiter a distance of Q = 28,455,252 km. In future these parameters may vary due to a large orbital distance from Jupiter and the orbital motion being disturbed by the Sun and other factors. Perhaps it is a captured asteroid (with a microscopic mass: ~1.4987×10¹³ kg – it equals 490 times less than a mountain like Giewont!), and in future will possibly return to heliocentric orbit.

    The orbital period is almost 2 earthly years, which means that the average speed of its celestial motion is only 0°30'14'' per day. When this motion was detected and compared to the changes in Jupiter's position, this body was classified as a true planetary satellite (and not a distant celestial body with its position projected near the planet).
    Other obstacle in detecting this moon earlier was its brightness of only 23.4^m (over 9.1 million times fainter than the faintest stars visible to naked eye). For comparison: Jupiter's brightness is about –2.7^m, so S/2003 J17 is shining fainter by about 26.1^m. The corresponding difference in brightness is over 27.5 billion times!