rings of Saturn
This mosaic of Saturn and its rings was taken close to equinox, when the Sun crosses the planet's equator. The images were captured on 12 August 2009 by the Cassini spacecraft. Source: NASA/JPL/Space Science Institute).
Saturn's rings and their shadow, imaged by the Cassini spacecraft.
Artist's concept of the giant infrared ring around Saturn.
|The main rings and divisions
|Artwork of the rings
Composed of swarms of ice-rock particles ranging in size from a centimeter to several meters across (and possibly even as large as a kilometer), Saturn's rings are much brighter (with an albedo of up to 0.6) than any other known planetary rings. Though some 170,000 kilometers wide (more if the tenuous outer portion of the E-ring is included), the rings are only about a kilometer or so thick and have a total mass of about 0.01 that of the Moon. When Earth occasionally moves through the same angle as the rings, which are slanted at 27°, they almost completely disappear from view. The rest of the time, only the outer A-ring, the brighter B-ring and the bluish inner C-ring are clearly visible through telescopes on Earth, together with several dark gaps, including the Cassini Division and the Encke Division, in which ring material is much sparser.
Four additional faint rings together with a wealth of other complex and puzzling features were discovered or confirmed by the Voyager probes. Among these features are puzzling radial inhomogeneities called spokes, first reported by amateur astronomers, that may be an effect caused by Saturn's magnetic field. The F-ring, a narrow, wavy structure just outside the A ring, is confined by two small satellites and consists of at least five individual strands with embedded knots that may be clumps of ring material or mini moons. Voyager 1 images (but not those of Voyager 2) also showed the F ring to have strange braided appearance. Complex tidal resonances exist between a number of Saturn's moons and the ring system. Some of the moons – the so-called shepherd moons, Atlas, Pandora, and Prometheus – are important in keeping the rings in place; Mimas seems to be responsible for the paucity of material in the Cassini division; while Pandora is located inside the Encke Division.
|Saturn's rings and divisions|
|D-ring||67,000||74,500||7,500||Very tenuous. Discovered in 1969|
|C-ring (Crepe ring)||74,500||92,000||17,500||Gauzy appearance. Discovered
by Bond in 1850
|Lyot (Maxwell) division||87,500||88,000||500|
|B-ring||92,000||117,500||25,500||The brightest ring|
|Cassini division||115,800||120,600||4,800||Discovered by Cassini in 1675|
Saturn's super-sized ring
In October 2009 the discovery was announced of a colossal new ring around Saturn. The ring only shows up in the infrared part of the spectrum and was found using NASA's Spitzer Space Telescope. The new ring, or belt, is so large that if it were visible in the night sky, it would span the width of two full Moons. The bulk of its material starts about 6 million kilometers (3.7 million miles) away from the planet and extends outward roughly another 12 million kilometers (7.4 million miles); its orbit is tilted 27° from the main ring plane. One of Saturn's farthest moons, Phoebe, circles within the ring, and is likely the source of its material.
The ring is tenuous, consisting of widely-dispersed particles of ice and dust. Spitzer's infrared eyes were able to spot the glow of the cool dust, which has a temperature of only about 80 kelvin (-193°C, -316°F).
The discovery may help solve an age-old riddle of one of Saturn's moons. Iapetus has a strange appearance – one side is bright and the other is really dark, in a pattern that resembles the yin-yang symbol. The astronomer Giovanni Cassini first spotted the moon in 1671, and years later figured out it has a dark side, now named Cassini Regio in his honor.
Saturn's supersized ring could explain how Cassini Regio came to be so dark. The ring is circling in the same direction as Phoebe, while Iapetus, the other rings and most of Saturn's moons are all going the opposite way. According to the scientists, some of the dark and dusty material from the outer ring moves inward toward Iapetus, slamming the icy moon like bugs on a windshield.