Ersa (moon)
Ersa /ˈɜːrsə/, also designated Jupiter LXXI, 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 alongside nine other Jovian moons on 17 July 2018 and it provisionally designated S/2018 J 1 by the Minor Planet Center, after observations were collected over a long enough time span to confirm the satellite's orbit. The satellite has been found in precovery observations as early as 6 August 2000.
Precovery image of Ersa taken by the Canada-France-Hawaii Telescope in February 2003 | |
| Discovery | |
|---|---|
| Discovered by | Scott S. Sheppard |
| Discovery site | Cerro Tololo Obs. |
| Discovery date | 11 May 2018 |
| Designations | |
Designation | Jupiter LXXI |
| Pronunciation | /ˈɜːrsə/ |
Named after | Ἔρσα Ersa |
Alternative names | S/2018 J 1 |
| Orbital characteristics | |
| Epoch 1 January 2000 (JD 2451545.0) | |
| Observation arc | 21.08 yr (7,701 d) |
| Earliest precovery date | 6 August 2000 |
| Satellite of | Jupiter |
| Group | Himalia group |
| Proper orbital elements | |
Proper semi-major axis | 11,401,000 km (0.07621 AU) AU |
Proper eccentricity | 0.116 |
Proper inclination | 29.1° (to ecliptic) |
Proper mean motion | 527.587231 deg / yr |
Proper orbital period | 0.68235 yr (249.229 d) |
Precession of perihelion | 8994.503 arcsec / yr |
Precession of the ascending node | 4232.058 arcsec / yr |
| Physical characteristics | |
Mean diameter | ≈3 km |
| Albedo | 0.04 (assumed) |
| 22.9 | |
| 15.9 | |
Ersa is part of the Himalia group, a tight cluster of prograde irregular moons of Jupiter that follow similar orbits to Himalia at semi-major axes between 11–12 million km (6.8–7.5 million mi) and inclinations between 26–31°. With an estimated diameter of 3 km (1.9 mi) for an absolute magnitude of 15.9, it is one of the smallest known members of the Himalia group.