Evidence points to existence moon of Saturn ring

The second largest moon of Saturn, Rhea, could have a small ring around him, reported Thursday a team of international researchers. This was the first time you find rings in a satellite instead of a planet. The findings of the Cassini spacecraft, published in the journal Science, will help scientists better understand how planets form, said Geraint Jones, who worked on the study while at the Max Planck Institute in Germany.

The four largest planets in the solar system, Jupiter, Neptune, Saturn and Uranus have rings, and Earth probably had one for billions of years before the moon existed, Jones said in a telephone interview"All planets when they were forming probably had rings at different times," explained the expert. "It's fascinating to find one possibly around a small body like Rhea, who is still with us today."

The Cassini spacecraft was launched in 1997 to examine Saturn. Last month scientists said evidence gathered by the European and U.S. joint mission indicates the presence of water beneath the frozen surface of another moon of Saturn, Enceladus.

Researchers believe that the latest data point to the existence of a ring because when Cassini recently flew past Rhea they detected a surprising lack of electrons around the moon. Rhea lies within a magnetized bubble that surrounds Saturn and contains trapped ions and electrons. Because of this, the researchers expected to see electrons trailing off closer to the surface as the moon absorbed.

Instead of this, the electrons disappeared much earlier-as if something was blocked, leaving a ring of debris as the most likely explanation, Jones said."There is evidence that something is absorbing electrons around this moon," said Jones. "A debris disk around the moon is the simplest explanation we can offer that would fit with the data we have."

The ring probably formed when a smaller body smashed into Rhea and threw a series of fragments that began orbiting the moon, said Iannis Dandouras, a planetary scientist at the National Center for Scientific Research in France who also collaborated in the study. The evidence of a ring is also interesting because it shows that the material was not incorporated into Rhea but launched into orbit, said Dandouras.

"For the first time we find a system of planetary rings around a satellite instead of a planet," said Dandouras. "A planetary ring tells the story about the historical formation of moons and planets."