Round and round it goes, and if it will ever give up its secrets, nobody knows. Saturn’s magnificent ring system continues to puzzle astronomers, with new observations by NASA’s Cassini spacecraft revealing dust rings that always point at the Sun and extra mass hiding in one of the brightest rings, which may be much older than previously thought.
The observations, discussed last week at a meeting of the American Astronomical Society’s Division of Planetary Sciences, include observations of propeller-shaped disturbances in the A ring, one of the planet’s two brightest rings (see image at right).
The first four of these features were found in 2006 and now a team led by Matthew Tiscareno of Cornell University in Ithaca, New York, US, has found many dozens more.
They are caused by moonlets as large as the Great Pyramid. Because the planet’s strong gravitational pull would have prevented smaller objects from sticking together to form moonlets so large, they are probably fragments of a kilometre-sized moon, says Joe Burns, also of Cornell.
Surprisingly, the propellers only show up in specific regions of the A ring. "My gut feeling is that there has been a recent break-up event," Burns told New Scientist.
In research led by Matthew Hedman, the Cornell team also discovered a number of narrow, slightly elongated rings whose longest axes always point at the Sun.
Apparently, the tiny particles in these ‘sunflower’ rings are somehow pushed around by sunlight, says Burns. However, he says he suspects that electrical charges in the surrounding rings also play a role.
The most surprising new ring result, however, is the obesity of Saturn’s brightest ring, the B ring. Researchers led by Glen Stewart of the University of Colorado in Boulder, US, studied how a star’s brightness varied when the ring passed in front of it. The observations revealed the existence of very dense dust clumps, implying that the ring is three times more massive than expected.
If the ring formed through the break-up of a solid body, this object must have been hundreds of kilometres across to account for the observed mass.
Such massive collisions were more probable in the early days of the solar system, suggesting that the B ring could be very old, says CU Boulder colleague Larry Esposito. "The origin of planetary rings is one of the big, unanswered questions of planetary science," he told New Scientist.
"If rings are young, it is only by good luck that we see them now. If they are ancient, rings probably always encircled the giant planets, as they do at the present time," he says. "Ancient rings would indicate rings are likely around giant planets detected around other stars."
However, Esposito notes that not all of Saturn’s rings are likely to be so primordial. "A moon or other B ring material could have been recently shattered to make the A ring," he adds.
"It’s an exciting find," says Burns. "But it now becomes much more difficult to explain the brightness of the ring particles," which are expected to be coated by dark meteoritic material over time. "The jury is still out on how the rings formed."
Via: New Scientist