similar. No surface details of Adrastea are known, due to the low resolution of available images. Orbit Adrastea is the smallest and second-closest member of the inner Jovian satellite family. It orbits Jupiter at a radius of about (1.806 Jupiter radii) at the exterior edge of the planet's main ring. 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. Adrastea is the second-fastest-moving of Jupiter's moons, with an orbital speed of 31.378 km/s. Relationship with Jupiter's rings Adrastea is the largest contributor to material in Jupiter's rings. This appears to consist primarily of material that is ejected from the surfaces of Jupiter's four small inner satellites by meteorite impacts. It is easy for the impact ejecta to be lost from these satellites into space. This is due to the satellites' low density and their surfaces lying close to the edge of their Hill spheres. It seems that Adrastea is the most copious source of this ring material, as evidenced by the densest ring (the main ring) being located at and within Adrastea's orbit. More precisely, the orbit of Adrastea lies near the outer edge of Jupiter's main ring. The exact extent of visible ring material depends on the phase angle of the images: in forward-scattered light Adrastea is firmly outside the main ring, but in back-scattered light (which reveals much bigger particles) there appears to also be a narrow ringlet outside Adrastea's orbit. Notes References Cited sources (discovery) (naming the moon) External links Adrastea Profile by NASA's Solar System Exploration Moons of Jupiter 19790708 Discoveries by David C. Jewitt Discoveries by G. Edward Danielson Moons with a prograde orbit