Adrastea (moon) No surface details of Adrastea are known, due to the low resolution of available images. 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
Stability of the Solar System essentially the distance from sun to earth). These are now known as the Kirkwood gaps. Some asteroids were later discovered to orbit in these gaps, but their orbits are unstable and they will eventually break out of the resonance due to close encounters with a major planet. Another common form of resonance in the Solar System is spin–orbit resonance, where the period of spin (the time it takes the planet or moon to rotate once about its axis) has a simple numerical relationship with its orbital period. An example is our own Moon, which is in a 1:1 spin–orbit resonance