S/2003 J 12

S/2003 J 12 is a natural satellite of Jupiter, and is one of the smallest known natural satellites in the Solar System. It was discovered by a team of astronomers from the University of Hawaii led by Scott S. Sheppard in 2003.^[5][1]

S/2003 J 12

S/2003 J 12 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	8 February 2003
Orbital characteristics[2]
Epoch 17 December 2020 (JD 2459200.5)
Observation arc	9.65 yr (3,525 d)
Earliest precovery date	10 December 2001
Semi-major axis	0.1441046 AU (21,557,740 km)
Eccentricity	0.3657005
Orbital period (sidereal)	–1.77 yr (–646.64 d)
Mean anomaly	295.36521°
Mean motion	0° 33m 24.215s / day
Inclination	154.69036° (to ecliptic)
Longitude of ascending node	127.52296°
Argument of perihelion	86.84711°
Satellite of	Jupiter
Group	Ananke group
Physical characteristics[3]
Mean radius	1.2 km
Mass	1.9×1013 kg
Mean density	2.6 g/cm3 (assumed)
Albedo	0.04 (assumed)[4]
Apparent magnitude	23.9[4]
Absolute magnitude (H)	17.0[2] 16.81±0.19 (R)[3]

S/2003 J 12 is about 2.4 km (1.5 mi) in diameter, and orbits Jupiter at an average distance of 21,600 Mm in 647 days, at an inclination of 155° to the ecliptic, in a retrograde direction and with an eccentricity of 0.366.^[2] It was initially thought to the innermost of the retrograde satellites of Jupiter, but recovery observations have shown that it is an ordinary member of the Ananke group.^[6]

Blink animation of S/2003 J 12 in CFHT precovery images from December 2001

Recovery images of S/2003 J 12 taken by the CFHT in August 2011

This moon was considered lost^{[7][8][9][10]} until late 2020, when it was recovered in archival CFHT images from 2001-2011 by amateur astronomer Kai Ly.^[6] The recovery of the moon was announced by the Minor Planet Center on 13 January 2021.^[2]