Rings of Jupiter

The planet Jupiter has a system of rings known as the rings of Jupiter or the Jovian ring system. It was the third ring system to be discovered in the Solar System, after those of Saturn and Uranus. It was first observed in 1979 by the Voyager 1 space probe and thoroughly investigated in the 1990s by the Galileo orbiter. It has also been observed by the Hubble Space Telescope and from Earth for several years. Ground-based observation of the rings requires the largest available telescopes. The planet Jupiter has a system of rings known as the rings of Jupiter or the Jovian ring system. It was the third ring system to be discovered in the Solar System, after those of Saturn and Uranus. It was first observed in 1979 by the Voyager 1 space probe and thoroughly investigated in the 1990s by the Galileo orbiter. It has also been observed by the Hubble Space Telescope and from Earth for several years. Ground-based observation of the rings requires the largest available telescopes. The Jovian ring system is faint and consists mainly of dust. It has four main components: a thick inner torus of particles known as the 'halo ring'; a relatively bright, exceptionally thin 'main ring'; and two wide, thick and faint outer 'gossamer rings', named for the moons of whose material they are composed: Amalthea and Thebe. The main and halo rings consist of dust ejected from the moons Metis, Adrastea, and other unobserved parent bodies as the result of high-velocity impacts. High-resolution images obtained in February and March 2007 by the New Horizons spacecraft revealed a rich fine structure in the main ring. In visible and near-infrared light, the rings have a reddish color, except the halo ring, which is neutral or blue in color. The size of the dust in the rings varies, but the cross-sectional area is greatest for nonspherical particles of radius about 15 μm in all rings except the halo. The halo ring is probably dominated by submicrometre dust. The total mass of the ring system (including unresolved parent bodies) is poorly known, but is probably in the range of 1011 to 1016 kg. The age of the ring system is not known, but it may have existed since the formation of Jupiter. A ring could possibly exist in Himalia's orbit. One possible explanation is that a small moon had crashed into Himalia and the force of the impact caused material to blast off Himalia. Jupiter's ring system was the third to be discovered in the Solar System, after those of Saturn and Uranus. It was first observed in 1979 by the Voyager 1 space probe. It is composed of four main components: a thick inner torus of particles known as the 'halo ring'; a relatively bright, exceptionally thin 'main ring'; and two wide, thick and faint outer 'gossamer rings', named after the moons of whose material they are composed: Amalthea and Thebe. The principal attributes of the known Jovian Rings are listed in the table. The narrow and relatively thin main ring is the brightest part of Jupiter's ring system. Its outer edge is located at a radius of about 129000 km (1.806 RJ;RJ = equatorial radius of Jupiter or 71398 km) and coincides with the orbit of Jupiter's smallest inner satellite, Adrastea. Its inner edge is not marked by any satellite and is located at about 122500 km (1.72 RJ). Thus the width of the main ring is around 6500 km. The appearance of the main ring depends on the viewing geometry. In forward-scattered light the brightness of the main ring begins to decrease steeply at 128600 km (just inward of the Adrastean orbit) and reaches the background level at 129300 km—just outward of the Adrastean orbit. Therefore, Adrastea at 129000 km clearly shepherds the ring. The brightness continues to increase in the direction of Jupiter and has a maximum near the ring's center at 126000 km, although there is a pronounced gap (notch) near the Metidian orbit at 128000 km. The inner boundary of the main ring, in contrast, appears to fade off slowly from 124000 to 120000 km, merging into the halo ring. In forward-scattered light all Jovian rings are especially bright. In back-scattered light the situation is different. The outer boundary of the main ring, located at 129100 km, or slightly beyond the orbit of Adrastea, is very steep. The orbit of the moon is marked by a gap in the ring so there is a thin ringlet just outside its orbit. There is another ringlet just inside Adrastean orbit followed by a gap of unknown origin located at about 128500 km. The third ringlet is found inward of the central gap, outside the orbit of Metis. The ring's brightness drops sharply just outward of the Metidian orbit, forming the Metis notch. Inward of the orbit of Metis, the brightness of the ring rises much less than in forward-scattered light. So in the back-scattered geometry the main ring appears to consist of two different parts: a narrow outer part extending from 128000 to 129000 km, which itself includes three narrow ringlets separated by notches, and a fainter inner part from 122500 to 128000 km, which lacks any visible structure like in the forward-scattering geometry. The Metis notch serves as their boundary. The fine structure of the main ring was discovered in data from the Galileo orbiter and is clearly visible in back-scattered images obtained from New Horizons in February–March 2007. The early observations by Hubble Space Telescope (HST), Keck and the Cassini spacecraft failed to detect it, probably due to insufficient spatial resolution. However the fine structure was observed by the Keck telescope using adaptive optics in 2002–2003.