Adrastea (moon) facts for kids

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Adrastea
Adrastea
Image of Adrastea taken by Galileo's solid state imaging system between November 1996 and June 1997.
Discovery
Discovered by David C. Jewitt
G. Edward Danielson
Discovery date July 8, 1979
Names
Orbit
Avgdistance from the center of its orbital path 129,000 km
How long it takes to complete an orbit 0.29826 d (7 h 9.5 min)
Average speed 31.378 km/s
Angle above the reference plane
("inclination")
0.03° (to Jupiter's equator)
What it orbits Jupiter
Size and other qualities
Measurements 20×16×14 km
Average radius 8.2 ± 2.0 km
Volume ~2,345 km³
Mass ~2×1015 kg
Average density 0.86 g/cm³ (assumed)
Surface gravity ~0.002 m/s² (0.0004 g)
Escape velocity ~0.008 km/s
Rotation period synchronous
Angle at which it turns
(in relation to its orbit)
zero
How much light it reflects ~0.1 ± 0.045
Avg. surface temp. ~122 K

Adrastea or Jupiter XV, is the second closest moon to Jupiter. It was found by David C. Jewitt and G. Edward Danielson in Voyager 2 probe photographs taken in 1979 and received the designation S/1979 J 1. In 1983, it was named after the mythological Adrastea, who was a daughter of Jupiter and Ananke.

Adrastea was the first moon to be found from images taken by an interplanetary spacecraft, rather than through telescopic photography.

Physical characteristics

Adrastea is non-spherical and measures 20x16x14 km³ across. What Adrastea is made of and the mass of Adrastea are not known, but assuming that its mean density is like that of Amalthea (~0.86 g/cm³) its mass can be estimated at ~2×1015 kg. Amalthea's density implies that moon is composed of water ice with a porosity of 10-15%, and Adrastea may be similar.

No surface details of Adrastea are known, due to the low resolution of available images.

Adrastée FDS 20630
Discovery image of Adrastea, taken on July 8, 1979 by Voyager 2. Adrastea is the dot in the very middle, straddling the line of the Jovian rings.

Orbit

Adrastea is the smallest and second closest member of the closer moons to Jupiter. It orbits Jupiter at ~129,000 km (1.806 Jupiter radii) within the planet's Main Ring. The orbital eccentricity of ~0.0015 and inclination of ~ 0.03° relative to the equator of Jupiter are very small.

Exploration

Adrastea was found in Voyager 1 and 2 images, but appeared only as a dot. The Galileo spacecraft was able to see its shape, but the images remain poor.


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