| S/2018 J 4 | |
| Discoverer: | Scott S. Sheppard |
| Discovery Site: | Cerro Tololo Obs. |
| Discovered: | 11 May 2018 |
| Alt Names: | S/2018 J 4 |
| Epoch: | 1 January 2000 (JD 2451545.0) |
| Observation Arc: | 4.55 yr (1,663 d) |
| P Eccentricity: | 0.177 |
| P Period: | +427.631071d--> |
| P Mean Motion: | 307.484673 |
| P Inclination: | 50.2° (to ecliptic) |
| Perihelion Rate: | N/A |
| Node Rate: | 6638.868 |
| Apsis: | jove |
| Satellite Of: | Jupiter |
| Group: | Carpo |
| Mean Diameter: | ≈ |
| Albedo: | 0.04 |
| Magnitude: | 23.5 |
| Abs Magnitude: | 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. The satellite has a diameter of about for an absolute magnitude of 16.7.
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. 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. On average, S/2018 J 4's orbit has a semi-major axis of 16.3e6km, an eccentricity of 0.18, and a very high inclination of 50° with respect to the ecliptic.
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. For example, the Lidov–Kozai resonance causes Carpo's eccentricity and inclination to fluctuate between 0.19–0.69 and 44–59°, respectively. 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.