Orbit
Adrastea is the smallest and second closest member of the inner Jovian satellite family. It orbits Jupiter at a radius of about 129,000 km (1.806 Jupiter radii) at the exterior edge of the planet's Main Ring. Adrastea is one of only three moons in the Solar System known to orbit its planet in less than the length of that planet's day—the other two being Jupiter's innermost moon Metis, and Mars' moon Phobos. The orbit has very small eccentricity and inclination—around 0.0015 and 0.03°, respectively. Inclination is relative to the equator of Jupiter.
Due to tidal locking, Adrastea rotates synchronously with its orbital period, keeping one face always looking toward the planet. Its long axis is aligned towards Jupiter, this being the lowest energy configuration.
The orbit of Adrastea lies inside Jupiter's synchronous orbit radius (as does Metis’s), and as a result, tidal forces are slowly causing its orbit to decay so that it will one day impact Jupiter. If its density is similar to Amalthea's then its orbit would actually lie within the fluid Roche limit. However, since it is not breaking up, it must still lie outside its rigid Roche limit.
Read more about this topic: Adrastea (moon)
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