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A tiny moon of Jupiter, averaging just 4km in diameter, which pursues an eccentric and highly inclined orbit around the giant planet. The moon's semi-major axis is 24,037,000 km, but because of its high orbital eccentricity its distance from Jupiter varies considerably over the course of its two-year orbit. It is inclined to Jupiter's orbital plane by -152.7°.*
Autonoe did not originally form as part of the Jovian system, but represents a fragment of an asteroid captured and broken apart by Jupiter's gravity. The most significant surviving element of this ancient asteroid is the moon Pasiphae (from which the entire set of related moons take their name, the Pasiphae Group). Within this group, only Pasiphae itself and the smaller Sinope exceeed 10 km in diameter.
The remaining moons in the group, including Autonoe, are all small pieces of the original asteroid. Autonoe is not in fact the smallest of these, and its fellow moonlets such as Eurydome and Sponde represent even smaller objects of the same kind.
* Inclination figures are calculated relative to the rotation of the primary planet (Jupiter in this case). Because Autonoe follows a retrograde orbit (that is, in the opposite direction to Jupiter's own rotation) its inclination value is negative. Leaving this factor aside, the moon's orbital plane is inclined at 27.1° to the equatorial plane of Jupiter.
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