Saturn has the most magnificent set of rings of any planet in the Solar System. This network of thousands of ringlets are separated by gaps, the largest of which is the Cassini Division.
Astronomers have now found that the largest of Saturn's rings is significantly larger than once believed, stretching for 7,000 times the diameter of the planet itself.
The Phoebe ring surrounding Saturn was discovered by astronomers using the Spitzer Space Telescope, who noticed the massive structure in infrared data. New examination, using the Wide-field Infrared Survey Explorer, reveals this feature is composed of dust, reaching to between 3.75 and 10 million miles away from its parent planet. Initial estimates placed the size of the Phoebe Ring between 4.8 and 7.7 million miles. Here, the dust is heated by energy from the distant sun, causing the material in glow in infrared wavelengths seen by astronomers.
"If Saturn were the size of a basketball, the ring from one side of the planet to the other would span two-thirds the length of a football field. Although the ring is huge, its dust particles are tiny," Ken Croswell wrote for Science magazine.
Researchers believe this faint ring may be formed from collisions between comets and far-flung satellites in the Saturnian system, such as Phoebe. This irregular moon, with a diameter of just 125 miles, is itself believed to be a former member of the distant Kuiper Belt of objects, captured by the gravitational forces of Saturn. Particles and debris released from these collisions could form a massive, faint ring such as the one examined in the latest study, researchers report.
"It's fascinating that this ring can exist. We're told in science textbooks that planetary rings are small and close to their parent planets — if they're too far away from their planets, moons form rather than rings. This discovery just turns that idea on its head — the universe is a more interesting and surprising place than we thought," Douglas Hamilton from the University of Maryland, College Park said.
Iapetus, one of the moons of Saturn, gave evidence of the existence of the ring before that structure was seen by astronomers. This satellite, covered in ice, is in a tidal lock with Saturn. Like our own moon, Iapetus always has one side facing its home planet. As it orbits Saturn, astronomers found the side that leads is covered in dark material, while the trailing side is white, as would be expected from ice. This suggested to researchers that the moon was traveling through a field of dust, which was collecting on the leading face.
Jupiter, the largest gas planet in our Solar System, may also possess a similar massive outer ring, researchers speculate.
Analysis of the Pheobe Ring of Saturn was published in the journal Nature.
