S/2018 J 4

S/2018 J 4
Discovery
Discovered by	Scott S. Sheppard
Discovery site	Cerro Tololo Obs.
Discovery date	11 May 2018
Designations
Alternative names	S/2018 J 4
Orbital characteristics
	Epoch 1 January 2000 (JD 2451545.0)
Observation arc	4.55 yr (1,663 d)
Satellite of	Jupiter
Group	Carpo
Proper orbital elements
Proper semi-major axis	16,328,500 km (0.109149 AU) AU
Proper eccentricity	0.177
Proper inclination	50.2° (to ecliptic)
Proper mean motion	307.484673 deg / yr
Proper orbital period	1.17079 yr; (427.631 d)
Precession of perihelion	N/A arcsec / yr
Precession of the ascending node	6638.868 arcsec / yr
Physical characteristics
Mean diameter	≈2 km
Albedo	0.04 (assumed)
Apparent magnitude	23.5
Absolute magnitude (H)	16.7

S/2018 J 4 is a small outer natural satellite of Jupiter discovered by Scott S. Sheppard on 11 May 2018, using the 4.0-meter Víctor M. Blanco Telescope at Cerro Tololo Observatory, Chile. It was announced by the Minor Planet Center on 20 January 2023, after observations were collected over a long enough time span to confirm the satellite's orbit.^[1] The satellite has a diameter of about 2 km (1.2 mi) for an absolute magnitude of 16.7.^[4]

S/2018 J 4 is an irregular moon of Jupiter on an highly inclined prograde orbit at an angle of 53° with respect to the ecliptic plane. It belongs to the same group as the similarly-inclined moon Carpo, which was long thought to be an outlier until the discovery of S/2018 J 4.^[4] Like all irregular moons of Jupiter, S/2018 J 4's orbit is highly variable over time due to gravitational perturbations by the Sun and other planets.^[5] On average, S/2018 J 4's orbit has a semi-major axis of 16.3 million km (10.1 million mi), an eccentricity of 0.18, and a very high inclination of 50° with respect to the ecliptic.^[3]

Like Carpo, S/2018 J 4's very high inclination subjects it to the Lidov–Kozai resonance, where there is a periodic exchange between its orbital eccentricity and inclination while its argument of pericenter oscillates about a constant value without apsidally precessing.^[6] For example, the Lidov–Kozai resonance causes Carpo's eccentricity and inclination to fluctuate between 0.19–0.69 and 44–59°, respectively.^[5] S/2018 J 4's argument of pericenter oscillates about 270° with respect to the ecliptic, which keeps its perijove always above Jupiter and apojove below Jupiter.^[3]

References

^ ^a ^b ^c "MPEC 2023-B51 : S/2018 J 4". Minor Planet Electronic Circulars. Minor Planet Center. 20 January 2023. Retrieved 20 January 2023.
^ "Planetary Satellite Discovery Circumstances". JPL Solar System Dynamics. NASA. Retrieved 20 January 2023.
^ ^a ^b ^c "Planetary Satellite Mean Elements". JPL Solar System Dynamics. NASA. Retrieved 13 February 2023.
^ ^a ^b ^c ^d ^e Sheppard, Scott S. "Moons of Jupiter". Earth & Planets Laboratory. Carnegie Institution for Science. Retrieved 20 January 2023.
^ ^a ^b Brozović, Marina; Jacobson, Robert A. (March 2017). "The Orbits of Jupiter's Irregular Satellites". The Astronomical Journal. 153 (4): 10. Bibcode:2017AJ....153..147B. doi:10.3847/1538-3881/aa5e4d. S2CID 125571053. 147.
^ Nesvorný, David; Alvarellos, Jose L. A.; Dones, Luke; Levison, Harold F. (July 2003). "Orbital and Collisional Evolution of the Irregular Satellites". The Astronomical Journal. 126 (1): 398–429. Bibcode:2003AJ....126..398N. doi:10.1086/375461. S2CID 8502734.