Adrastea (moon)
Adrastea (/ædrəˈstiːə/), also known as Jupiter XV, is the second by distance, and the smallest of the four inner moons of Jupiter. It was discovered in photographs taken by Voyager 2 in 1979, making it the first natural satellite to be discovered from images taken by an interplanetary spacecraft, rather than through a telescope. It was officially named after the mythological Adrasteia, foster mother of the Greek god Zeus—the equivalent of the Roman god Jupiter.
Image of Adrastea taken by Galileo spacecraft between November 1996 and June 1997 | |
| Discovery | |
|---|---|
| Discovered by |
|
| Discovery date | 8 July 1979 |
| Designations | |
| Pronunciation | /ædrəˈstiːə/ |
Named after | Ἀδράστεια Adrasteia |
| Adjectives | Adrastean /ædrəˈstiːən/ |
| Orbital characteristics | |
Mean orbit radius | 129000 km |
| Eccentricity | 0.0015 |
Orbital period (sidereal) | 0.29826 d (7 h, 9.5 min) |
Average orbital speed | 31.378 km/s |
| Inclination | 0.03° (to Jupiter's equator) |
| Satellite of | Jupiter |
| Physical characteristics | |
| Dimensions | 20 × 16 × 14 km |
Mean radius | 8.2±2.0 km |
| Volume | ≈ 2345 km3 |
Synodic rotation period | synchronous |
| zero | |
| Albedo | 0.10±0.045 |
| Temperature | ≈ 122 K |
Adrastea is one of the few moons in the Solar System known to orbit its planet in less than the length of that planet's day. It orbits at the edge of Jupiter's main ring and is thought to be the main contributor of material to the rings of Jupiter. Despite observations made in the 1990s by the Galileo spacecraft, very little is known about the moon's physical characteristics other than its size and the fact that it is tidally locked to Jupiter.