7th Largest Moon of Jupiter - Thebe (4th Moon outwards from Jupiter)

Thebe is the second largest of the inner satellites of Jupiter and the seventh largest moon overall in size. Thebe is the 46th largest moon in the Solar System currently known.

Discovery

Thebe was discovered by Stephen P. Synnott in images from the Voyager 1 space probe taken on March 5, 1979, while orbiting around Jupiter.

After its discovery by Voyager 1, Thebe was photographed by Voyager 2 space probe in 1980. And later, in more detail, by the Galileo orbiter in the 1990s.

Naming

Thebe was initially given the provisional designation S/1979 J2.

In 1983 the moon was officially named after the mythological nymph Thebe who was a lover of Zeus — the Greek equivalent of Jupiter.

Stats

Diameter (mean): 99 km

Semi-major axis: 221,889 km

Orbital Period: 0.675 days

Rotation Period: Synchronous

Orbit

Thebe is the outermost of the inner Jovian moons.

The orbit of Thebe lies near the outer edge of the Thebe Gossamer Ring, which is composed of the dust ejected from the satellite. After ejection the dust drifts in the direction of the planet under the action of Poynting-Robertson drag forming a ring inward of the moon.

Similarly to all inner satellites of Jupiter, Thebe rotates synchronously with its orbital motion, thus keeping one face always looking toward Jupiter.

Thebe's 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.

Physical characteristics

Thebe is irregularly shaped, with the closest ellipsoidal approximation being 116×98×84 km.

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).