have excited its inclination and eccentricity (in a mean-motion resonance the ratio of orbital periods of two bodies is a rational number like m:n). Amalthea's orbit lies near the outer edge of the Amalthea Gossamer Ring, which is composed of the dust ejected from the satellite. Physical characteristics The surface of Amalthea is very red. This color may be due to sulfur originating from Io or some other non-ice material. Bright patches of less red tint appear on the major slopes of Amalthea, but the nature of this color is currently unknown. The surface of Amalthea is slightly brighter than surfaces of other inner satellites of Jupiter. There is also a substantial asymmetry between leading and trailing hemispheres: the leading hemisphere is 1.3 times brighter than the trailing one. The asymmetry is probably caused by the higher velocity and frequency of impacts on the leading hemisphere, which excavate a bright material—presumably ice—from the interior of the moon. Amalthea is irregularly shaped, with the best ellipsoidal approximation being . From this, Amalthea's surface area is likely between 88,000 and 170,000 square kilometers, or somewhere near 130,000. Like all other inner moons of Jupiter it is tidally locked with the planet, the long axis pointing towards Jupiter at all times. Its surface is heavily scarred by craters, some of which are extremely large relative to the size of the moon: Pan, the largest crater, measures 100 km across and is at least 8 km deep. Another crater, Gaea, measures 80 km across and is likely twice as deep as Pan. Amalthea has several prominent bright spots, two of which are named. They are Lyctos Facula and Ida Facula, with width reaching up to 25 km. They are located on the edge of ridges. Amalthea's irregular shape and large size led in the past to a conclusion that it is a fairly strong, rigid body, where it was argued that a body composed of ices or other weak materials would have been pulled into a more spherical shape by its own gravity. However, on 5 November 2002, the Galileo orbiter made a targeted flyby that came within 160 km of Amalthea and the deflection of its orbit was used to compute the moon's mass (its volume had been calculated previously—to within 10% or so—from a careful analysis of all extant images). In the end, Amalthea's density was found to be as low as