Ananke (moon)
Moon of Jupiter
From Wikipedia, the free encyclopedia
Ananke (/əˈnæŋki/), also known as Jupiter XII, is one of the larger retrograde irregular moons of Jupiter.
Ananke photographed by the Haute-Provence Observatory in August 1998 | |
| Discovery[1] | |
|---|---|
| Discovered by | Seth B. Nicholson |
| Discovery site | Mt. Wilson Observatory |
| Discovery date | 28 September 1951 |
| Designations | |
Designation | Jupiter XII |
| Pronunciation | /əˈnæŋkiː/[2] |
Named after | Ἀνάγκη Anagkē |
| Adjectives | Anankean /ænəŋˈkiːən/[3] |
| Orbital characteristics[4] | |
| Epoch 17 December 2020 (JD 2459200.5) | |
| Observation arc | 69.05 yr (24,338 days) |
| 0.1406602 AU (21,042,470 km) | |
| Eccentricity | 0.1747248 |
| –623.59 d | |
| 339.61045° | |
| 0° 34m 38.281s / day | |
| Inclination | 148.67482° (to ecliptic) |
| 86.44368° | |
| 135.63033° | |
| Satellite of | Jupiter |
| Group | Ananke group |
| Physical characteristics | |
| 29.1±0.6 km[5] | |
| Mass | 1.68×1016 kg (calculated) |
Mean density | 1.30 g/cm3 (assumed)[6] |
| 8.31±0.15 h[7] | |
| Albedo | 0.038±0.006[5] |
Spectral type | P[5] |
| 18.9[8] | |
| 11.7[4] | |
Discovery and naming
It was discovered by Seth Barnes Nicholson at Mount Wilson Observatory in 1951.[1]
It is named after the Greek mythological Ananke, the personification of necessity, and the mother of the Moirai (Fates) by Zeus. Ananke did not receive its present name[9] until 1975;[10] before then, it was simply known as Jupiter XII. It was sometimes called "Adrastea"[11] between 1955 and 1975 (Adrastea is now the name of another satellite of Jupiter).
Orbit
Ananke orbits Jupiter (on average 21,042,470 km) on a high-eccentricity (0.174) and high-inclination (149° to ecliptic) retrograde orbit. They are continuously changing due to solar and planetary perturbations.
Ananke gives its name to the Ananke group, a group of irregular retrograde moons orbiting Jupiter at a distance ranging between 19–22 million km, with inclinations between 144 and 156°, and eccentricities between 0.10 and 0.30.
Physical characteristics
From infrared thermal measurements by the WISE spacecraft, Ananke's albedo is measured at 3.8%, corresponding to a diameter of 29.1 kilometres.[5]
In the visible spectrum, Ananke appears neutral to light-red (colour indices B-V=0.90 V-R=0.38).[12] The infrared spectrum is similar to P-type asteroids but with a possible indication of water.[13]
The rotation period was determined to be approximately 8 hours and 18.6 minutes with a peak amplitude of about ~0.4 magnitudes.[7] This was regarded by a later paper as uncertain due to the short observation periods.[14]
Origin
Ananke probably did not form near Jupiter but was captured by Jupiter later. Given these orbital elements and the physical characteristics known so far, Ananke is thought to be the largest remnant[15] of an original break-up, forming the Ananke group.[16][12]
