S/2003 J 2

S/2003 J 2 is a retrograde irregular satellite of Jupiter. The moon was discovered on 5 February 2003 by a team of astronomers from the University of Hawaii led by Scott S. Sheppard and David C. Jewitt, and was later announced on 4 March 2003.^[4][5] It was initially thought to be Jupiter's outermost known moon until recovery observations disproved this in 2020.^[6]

S/2003 J 2

S/2003 J 2 imaged by the Canada-France-Hawaii Telescope during follow-up observations in February 2003
Discovery [1]
Discovered by	Scott S. Sheppard et al.
Discovery site	Mauna Kea Obs.
Discovery date	5 February 2003
Orbital characteristics [2]
Epoch 17 December 2020 (JD 2459200.5)
Observation arc	16.42 yr (5,996 d)
Earliest precovery date	11 December 2001
Semi-major axis	0.1373976 AU (20,554,390 km)
Eccentricity	0.2776569
Orbital period (sidereal)	–1.65 yr (–602.02 d)
Mean anomaly	114.43587°
Mean motion	0° 35m 52.742s / day
Inclination	149.20392° (to ecliptic)
Longitude of ascending node	50.46976°
Argument of perihelion	224.95527°
Satellite of	Jupiter
Group	Ananke group
Physical characteristics
Mean diameter	≈2 km[3]
Albedo	0.04 (assumed)[3]
Apparent magnitude	23.2[3]
Absolute magnitude (H)	16.7[2]

S/2003 J 2 is about 2 km (1.2 mi) in diameter, and orbits Jupiter at an average distance of about 20,600,000 kilometers (20.6 gigametres (0.138 AU)) in roughly 600 days, at an inclination of around 149° to the ecliptic and with an eccentricity of 0.28. The moon was initially assumed to be part of the Pasiphae group, but is now known to be part of the Ananke group after it was recovered in 2020.^[1][6]

S/2003 J 2 and several bright background stars and galaxies imaged by the CFHT in April 2003

The moon was considered lost^{[7][8][9][10]} until 2020, when it was recovered by Sheppard and independently by amateur astronomer Kai Ly.^[6] The recovery of the moon was announced by the Minor Planet Center on 26 January 2021.^[2]