New Horizons obtained 400 ring images of the Jovian ring system using the Long Range Reconnaissance Imager (LORRI). This camera has a broad bandpass spanning wavelengths λ = 0.35 to 0.85 µm. The ring was imaged at phase angles 7°-159°. In addition, one sequence of near-IR spectra (λ = 1.25 to 2.5 µm) was obtained by the Linear Etalon Imaging Spectral Array (LEISA) for compositional studies. Two ring rotation movies during Jupiter approach were used to search for small moons embedded within the system. These bodies might serve as source bodies for the prevalent ring dust. No moons were detected down to a threshold of 500 m radius, suggesting a sharp cutoff in the population of inner Jovian moons below 8-km Adrastea. Although this search focused on the main Jovian ring, any 1-km moons from orbital radius r = 100,000 km to beyond the orbit of Amalthea (r = 181,000 km) should have been detected multiple times. More surprisingly, the ring revealed two clusters of tiny clumps, one pair and one set of three. These are definitively not moons because they have longitudinal extents of a few tenths of a degree. Separations between clumps are 2 to 4° but are not uniform. These clump families both orbit within a brightness peak just interior to the orbit of Adrastea, at r = 128,740 km. Their origin is unknown. They are not visible at high phase angles, indicating that they are composed primarily of larger "parent” bodies, not dust. They are definitely not related to a clump detected in Cassini images of the Jovian ring from December 2000, indicating that at least some ring clumps are transient. The large quadrant asymmetries reported in earlier images from Voyager and Galileo are completely absent in the new data.
AAS/Division for Planetary Sciences Meeting Abstracts #39
- Pub Date:
- October 2007