An artist’s concept of the expansive “Phoebe ring” circling Saturn.
Saturn’s faint outermost ring cuts a massive swath as it circles around its home planet, spanning an area of sky nearly 7,000 times larger than Saturn itself, new research shows.
Analysis of images taken by NASA’s infrared sky-mapping WISE telescope also show that the ring, discovered in 2009, is comprised mostly of small particles. Rocks about as big as soccer balls make up only a small fraction of the ring’s population. It’s an unusual mix, scientists write in an article in this week’s Nature, prompting a new look at the physics behind ring assembly and longevity.
Saturn’s tenuous, outermost ring, called the “Phoebe ring,” is believed to contain dust and ice particles ejected from Saturn’s outer moon, Phoebe, after micrometeoroid and other impacts.
The ring is tilted at an angle of 27 degrees, relative to the other seven known rings, and like Phoebe, orbits Saturn in a backwards, or retrograde, direction.
NASA’s infrared Spitzer space telescope caught sight of the ring in 2009 and scientists using images from the Saturn-orbiting Cassini spacecraft ferreted out the first optical view in 2012.
The new research shows the Phoebe ring begins about 3.7 million miles away from Saturn and fans out a “surprisingly” distant 10 million miles, with a vertical expanse of about 1.5 million miles, making it well over 10 times larger than what was previously believed to be Saturn’s largest ring, the E ring, astronomer Douglas Hamilton, with the University of Maryland, and colleagues write in this week’s Nature.
“New observations of this ring provide a detailed view of the full disk and enable the structure and composition of the ring to be determined, which may give clues about how the ring formed,” notes Nature in a summary of the research.