B, V photometry of Thebe (JXIV)

Abstract

Thebe (JXIV), a small inner moon of Jupiter, was discovered by Synnott in 1980 from Voyager images. It orbits in a severe environment of bombardment by high-energy charged particles trapped in Jupiter's magnetosphere and other contaminants originating on Io. Since Thebe is too small for its surface to be affected by endogenic processes, Thebe's surface is useful as a probe for the remote sensing of this environment. B and V photometry of Thebe was obtained relative to Amalthea (JV). A TI 800 × 800 CCD chip was used with the USNO 61-in. astrometric reflector at Flagstaff. The results show Thebe to be 0.5 mag brighter in V on the leading side, near the eastern elongation, than on the trailing side, near the western elongation, suggesting synchronous rotation. A mean opposition magnitude, V = 15.7, is obtained when combining these results with Millis' photometry of JV. The average albedo in V, 0.04, is similar to that of JV and agrees with Synnott's discovery observations. A ( B - V) of 1.3 makes Thebe one of the reddest moons in the Solar System and suggests that it too has been resurfaced by sulfur from Io. Contrary to expectations, Thebe is found to be 0.2 mag bluer than Amalthea, suggesting other contaminants. Thebe also shares several photometric patterns with the Galileans and, thus, links the inner satellite system with the Galilean system. This suggests that the magnetospheric processes which have modified the surfaces of the Galileans have also modified the surfaces of the inner satellites. An implication of this conclusion is that the leading faces of the innermost satellites, Adrastea (JXV) and Metis (JXVI), should be darkened and reddened.