Floored of the Rings: Cassini Baffles Scientists at Saturn
For the past few months (02/28/2005), the Cassini spacecraft has had a ringside seat at Saturn, with high inclination orbits that have provided the best viewing angles since orbit insertion last year (07/01/2004). Cassini scored, as it soared around and around the horde of ring particles, and poured its stored data toward waiting scientists at Earth. They weren’t bored. News about the rings has just been announced by the American Astronomical Society Planetary Sciences Division at their meetings at Cambridge. The findings underscored a growing feeling that cannot be ignored: the rings are youthful and active.
- D is for Detached: The D ring (picture) shows dramatic changes since the Voyagers flew by in 1981. Parts have detached and migrated 125 miles toward Saturn (picture). It has also grown noticeably dimmer. See: MSNBC News.
- B is for Bumpy: Particles in the main B and A rings show a fluffy, airy appearance rather than being hard like ice cubes. This was determined from infrared thermal comparisons between lit and unlit sides of the rings, which showed a 15° K difference (diagram). Such a sharp thermal gradient implies that the particles spin slowly enough to cool off when in shadow – an unexpected result considering the density of particles and high probability of collisions. See: BBC News and News@Nature.
- A is for Animated: Ultraviolet measurements of the A ring revealed clumps of material continually forming and reforming (pictureEurekAlert.
- F is for Flimsy: The thin F-ring outside the main rings may be unstable or ephemeral, claim Cassini scientists. They found an unexpected spiral band wrapping around the planet (picture). This spiral forms by a different mechanism than the density waves and bending waves observed in the main rings (picture). It is apparently caused by small embedded moonlets (picture) that pass through the dense parts of the F-ring and pull material out, which follow spiral paths back to their resonant positions. It is unusual for a moonlet to be able to exist at this radial distance, near the Roche limit of Saturn, where tidal forces are strong enough to tear bodies apart. See: New Scientist and Science Daily.
- G is for Gossamer: The F and G rings contain particles the size of dust or smoke. The tenuous G ring, just outside the F ring, was found to contain a partial ring, or ring arc (picture), similar to those found at Neptune. See: EurekAlert.
- E is for Enceladus-Fed: It now appears fairly certain that at least some of the E-ring particles are being supplied from eruptions at the south pole of Enceladus (08/30/2005). See: Cassini press release.
The Cassini and Cassini Imaging websites are good sources for the latest images. See the Cassini multimedia page for latest press images and images by category. As the MSNBC article highlighted, scientists are “baffled” by many of these findings. They show Saturn’s rings to be highly dynamic, ephemeral structures that are undergoing rapid changes.
By scientific consensus now, Saturn’s rings are young. If so, how could they survive for anywhere near the assumed age of the solar system? Why should we be “lucky” enough to see them now, when humans just happen to be around to observe them? These findings have not dimmed such questions that were asked back in 1981, when Voyager 1 and 2 first provided glimpses into the dynamic processes at work. Rather, they have put these philosophical issues under the spotlight. If this were the only example of an apparently young phenomenon in a hoary old solar system, it would be one thing, but… keep reading.