Letters

E Ring (Saturn)

How It's Used

“After passing through the ‘E-ring,’ the outermost of the concentric hoops of ice and rock debris that orbit Saturn, Cassini is to circle the planet at least six dozen times, using additional assists from the gravity of Titan to adjust its path. Cassini's agenda of 27 scientific investigations includes transmission of up to 500,000 images, studies of the ring system and of suspected features such as ice-spewing water volcanoes on the moon Enceladus, one of Saturn's 18 moons.”

“It is not known for sure if the rings of Saturn date from very early in the history of the solar system or are comparatively recent, but NASA suggests that they formed at different times and in different processes.

“For example, Cassini found what NASA describes as ‘a great plume of icy material blasting from the moon Enceladus,’ believed to be a major source of material for the E ring. Moreover, NASA says, ‘most of the planet's small, inner moons appear to orbit within partial or complete rings formed from particles blasted off their surfaces by impacts of micrometeoroids.’”

“Previously, the largest-known planetary rings were Jupiter's ‘gossamer rings’ and Saturn's E ring—broad sheets of dust which extend to five to ten times the radius of their planets. The newly discovered ring [around Saturn], which contains ice particles as well as dust, is very faint. In a cubic kilometre of space there are about 20 particles. 'It's very, very tenuous. If you were standing in the ring itself, you wouldn't even know it,' said Dr [Anne] Verbiscer.

“The ring was discovered with Nasa's Spitzer Space Telescope, which has an infrared camera that can pick up longwavelength light that is invisible to the naked eye. The telescope, which is currently 66 million miles from Earth in orbit around the Sun, picked up a faint glow from the ring's cool dust particles. ‘We were not expecting to find rings associated with moons,’ said Professor Carl Murray, from the Astronomy Unit at Queen Mary, University of London. ‘Now we think if you've got a moon that's being continually bombarded with debris, it's likely that a ring will form.’”

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