When, exactly, Saturn acquired its iconic ring-system is a longstanding point of debate among planetary scientists. Some maintain the structures formed relatively recently, while others argue they formed long ago. Now, newly collected data suggest the rings likely formed 4.4-billion years ago, lending strong support to the latter camp.
Above: Saturn, as photographed by Cassini (and composited by Gordan Ugarkovic) earlier this year from a rare overhead vantage point.
The findings, presented by Sascha Kempf and his colleagues this week at the annual meeting of the American Geophysical Union, are based on measurements made by NASA's Cassini spacecraft. SPACE.com's Mike Wall has the details:
Kempf and his colleagues used Cassini's Cosmic Dust Analyzer instrument to measure just how frequently [tiny particles of rocky material, contributed by micrometeor bombardment] cruise through the Saturn system.
They found that a surprisingly small amount of dusty material comes into contact with the rings. On average, just 0.0000000000000000001 grams — or, in scientific notation, 10^-19 g — of dust per square centimeter zooms through space every second at a distance of five to 50 Saturn radii from the planet.
Having measured this low rate of dust recruitment, the team then calculated that the rings have likely existed for about 4.4 billion years.
"It would be consistent with an old ring system," Kempf said.
Kempf and his colleagues were also able to reconstruct the orbits of many of these particles, finding that the lion's share likely come from the Kuiper Belt, the ring of icy bodies beyond Neptune's orbit. However, some of the dust probably hails from the even more distant Oort Cloud and some from interstellar space, Kempf said.