One of the rings of Saturn is illuminated and off in strange ways. When "Voyager 1" visited the planet in 1980, the ring was dim, but it occasionally flashed bright spots. By the time when the place came "Cassini" (in 2004), the spots are gone, but the brightness of the rings has doubled.
The first F-ring discovered the "Pioneer 11" in 1979. While the larger part of the inner rings have a clear edge, the ring F — the outermost of the key — consists of a thin central band, surrounded by a diffuse haze of tiny particles of ice that curls around her.
Most curls explains the influence of Prometheus, a satellite that travels just inside the ring F. Moving in an elliptical orbit, Prometheus is coming to the ring, it is deleted from it. Sometimes he even takes away the material in the latter.
Despite these changes sometimes hourly, it was thought that the whole ring is stable. Therefore, comparison of images obtained "Voyager" and "Cassini" has led experts puzzled. Robert French Institute of SETI (USA) and his colleagues found that almost a quarter of a century, the ring was not only brighter, but also three times as wide, and in addition, to halve its transparency.
"All of this means that today there is much more dust than before", — said Mr. French. Tiny particles scatter more sunlight, so the ring and seems brighter.
The first thought that visited scientists, was the fact that once again blame Prometheus. However, during the time when the satellite was near the ring (in the first five years of being "Cassini" in the Saturn system), it has not changed.
Stranger still looks the fact that the ring has a dimmer for the nine months between visits Saturn first and second "Voyager."
As for the bright spots, the "Hubble" saw similar scenes back in 1995. By 2004, they were, as already mentioned, have largely disappeared. But in December 2006, one very bright spot appeared. It would increase the average brightness of the ring by 84% and lasted for more than two years. Further study showed that it broke out, when the central part of the F ring hit mini-satellite S/2004S6. Perhaps the other spots have a similar origin?
Group Mr. Frencha offers the following explanation. When Prometheus comes very close, its gravity accelerates particles of ice. As a result of clots, which managed to form a ring, broken, and it glows brightly. Once Prometheus receding ring calms down. Particles begin to clump together again, turning into giant snowballs that grow under its own gravity. Prometheus can pull some of these mini-satellites outside the ring. After some time they again fall into the ring and explode, turning into bright clouds.
This process saw the "Voyager" in 1980 and 1981. The next time a meeting was held with a ring of Prometheus in 1990 — hence those spots that he had seen "Hubble" in 1995. When arrived at Saturn "Cassini", Prometheus had just approached the ring, increasing its brightness, but to form a mini-satellite deal is not reached.
The truth of the hypothesis can be established in the year 2017, when Prometheus will be in the same position relative to the ring, as in the days of "Voyager." "Cassini" at that time still to remain in service.