Thebe (moon) - Physical Characteristics

Physical Characteristics

Thebe is irregularly shaped, with the closest ellipsoidal approximation being 116×98×84 km. Its surface area is probably between 31,000 and 59,000 (~45,000) km2. Its bulk density and mass are not known, but assuming that its mean density is like that of Amalthea (around 0.86 g/cm³), its mass can be estimated at roughly 4.3 × 1017 kg.

Similarly to all inner satellites of Jupiter, Thebe rotates synchronously with its orbital motion, thus keeping one face always looking toward the planet. Its orientation is such that the long axis always points to Jupiter. At the surface points closest to and furthest from Jupiter, the surface is thought to be near the edge of the Roche lobe, where Thebe's gravity is only slightly larger than the centrifugal force. As a result, the escape velocity in these two points is very small, thus allowing dust to escape easily after meteorite impacts, and ejecting it into the Thebe Gossamer Ring.

The surface of Thebe is dark and appears to be reddish in color. There is 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 (probably ice) from the interior of the moon. The surface of Thebe is heavily cratered and it appears that there are at least three or four impact craters that are very large, each being roughly comparable in size to Thebe itself. The largest (diameter about 40 km) crater is situated on the side that faces away from Jupiter, and is called Zethus (the only surface feature on Thebe to have received a name). There are several bright spots at the rim of this crater.