THE first complete images of Neptune鈥檚 outer rings to be taken in over a decade show that some parts of them have dramatically deteriorated and one section is close to disappearing altogether.
The Voyager 2 spacecraft first photographed the rings in 1989. The images showed four bright arcs in the faint outermost 鈥淎dams鈥� ring. These arcs spanned only about one-ninth of the ring in total. In 2002 and 2003, Imke de Pater of the University of California, Berkeley, and colleagues used the 10-metre Keck telescope in Hawaii to look at the ring again. They have now analysed the images and found that all the arcs seem to have decayed, while one arc, called Libert茅, has faded considerably since the Voyager observations (Icarus, vol 174, p 263).
Team member Eugene Chiang says that if the trend continues, Libert茅 will be gone in a century. The results suggest that whatever is causing the arcs to deteriorate is acting faster than any mechanism regenerating them. 鈥淭he system is not in equilibrium,鈥� says Chiang. 鈥淥ur whole understanding is up in the air.鈥�
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