S/2021 J 4

S/2021 J 4
Discovery
Discovered by	Scott S. Sheppard
Discovery site	Las Campanas Obs.
Discovery date	14 August 2021
Orbital characteristics
	Epoch 25 February 2023 (JD 2460000.5)
Observation arc	1.17 yr (427 d)
Semi-major axis	0.1533891 AU (22,946,680 km)
Eccentricity	0.1585459
Orbital period (sidereal)	–1.94 yr (–710.13 days)
Mean anomaly	102.76481°
Mean motion	0° 30m 25.027s / day
Inclination	164.54657° (to ecliptic)
Longitude of ascending node	218.88401°
Argument of perihelion	217.30730°
Satellite of	Jupiter
Group	Carme group
Physical characteristics
Mean diameter	≈1 km
Apparent magnitude	24.0
Absolute magnitude (H)	17.4

Last updated December 29, 2025

S/2021 J 4 is a small outer natural satellite of Jupiter discovered by Scott S. Sheppard on 14 August 2021, using the 6.5-meter Magellan-Baade Telescope at Las Campanas Observatory, Chile. It was announced by the Minor Planet Center on 19 January 2023, after observations were collected over a long enough time span to confirm the satellite's orbit.^[1]

S/2021 J 4 is part of the Carme group, a tight cluster of retrograde irregular moons of Jupiter that follow similar orbits to Carme at semi-major axes between 22–24 million km (14–15 million mi), orbital eccentricities between 0.2 and 0.3, and inclinations between 163 and 166°.^[3] It has a diameter of about 1 km (0.62 mi) for an absolute magnitude of 17.4, making it one of Jupiter's smallest known moons.^[3]

References

1 2 3 4 "MPEC 2023-B40 : S/2021 J 4". Minor Planet Electronic Circulars. Minor Planet Center. 19 January 2023. Retrieved 20 January 2023.
↑ "Planetary Satellite Discovery Circumstances". JPL Solar System Dynamics. NASA. Retrieved 10 January 2023.
1 2 3 4 Sheppard, Scott S. "Moons of Jupiter". Earth & Planets Laboratory. Carnegie Institution for Science. Retrieved 10 January 2023.

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[MPEC-2023-B40-1] 1 2 3 4 "MPEC 2023-B40 : S/2021 J 4". Minor Planet Electronic Circulars. Minor Planet Center. 19 January 2023. Retrieved 20 January 2023.

[jplsats-disc-2] "Planetary Satellite Discovery Circumstances". JPL Solar System Dynamics. NASA. Retrieved 10 January 2023.

[SheppardMoons-3] 1 2 3 4 Sheppard, Scott S. "Moons of Jupiter". Earth & Planets Laboratory. Carnegie Institution for Science. Retrieved 10 January 2023.

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v t e Moons of Jupiter
Listed in increasing approximate distance from Jupiter
Inner moons	Metis Adrastea Amalthea Thebe
Galilean moons	Io Europa Ganymede Callisto
Themisto	Themisto
Himalia group (9)	Leda Ersa S/2018 J 2 Himalia Pandia Lysithea Elara S/2011 J 3 Dia
Carpo group (2)	S/2018 J 4 Carpo
Valetudo	Valetudo
Ananke group (27)	Euporie Jupiter LV Eupheme S/2021 J 3 Jupiter LII Jupiter LIV Mneme Euanthe S/2003 J 16 Harpalyke Orthosie Helike S/2021 J 2 Praxidike Jupiter LXIV S/2021 J 1 S/2003 J 12 Jupiter LXVIII Thelxinoe Thyone S/2003 J 2 S/2022 J 3 Ananke Iocaste S/2017 J 10 Hermippe Jupiter LXX
Carme group (31)	S/2016 J 3 S/2022 J 1 Jupiter LXIX Pasithee S/2021 J 6 S/2003 J 24 Chaldene Jupiter LXIII Isonoe S/2017 J 11 Kallichore S/2021 J 4 Erinome Kale Eirene Aitne Eukelade S/2022 J 2 Arche Taygete Jupiter LXXII Carme Herse Jupiter LXI Jupiter LI S/2003 J 9 Jupiter LXVI Kalyke S/2003 J 10 S/2018 J 3 S/2021 J 5
Pasiphae group (18)	Philophrosyne Eurydome Jupiter LVI S/2003 J 4 S/2016 J 4 Jupiter LXVII Hegemone Pasiphae Sponde Megaclite Cyllene Sinope Jupiter LIX Aoede Autonoe Callirrhoe S/2003 J 23 Kore
See also	Rings of Jupiter Jupiter's moons in fiction
Category