University and University of Maryland researchers have discovered Saturn's largest ring, potentially solving a 300-year-old astronomical mystery.
Researchers were able to confirm the existence of the ring using the Spitzer Space Telescope, which includes an infrared instrument, University Astronomy research scientist Anne Verbiscer said.
The search for the ring began after observing unusual light reflected from Phoebe, a distant outer moon of Saturn, Verbiscer said. She and University Astronomy Prof. Mike Skrutskie theorized that something may have been hitting the moon, throwing dust and other particles, confirming the ring's existence.
It also helps to solve a mystery that has surrounded another of Saturn's moons, Verbiscer said. Iapetus, a closer moon discovered in the late 17th century, was noted for its "particularly strange appearance," she said. Called the "yin yang moon," Iapetus is extremely bright on one side and dark on the other.
For centuries, astronomers were unable to account for the appearance, though in the past few decades some had theorized a connection between Phoebe and Iapetus, Verbiscer said. The ring provides a critical link between the two moons, she said.
"The ring itself is generated from debris that's launched from Phoebe by impacts," Skrutskie said, and its existence supports the theory that debris from Phoebe has been working its way in and coating a side of Iapetus, in the same way bugs collect on a windshield.
"That's been a theory," Skrutskie said, "The discovery of this ring shows the source of that material is actually there."
Throughout the history of the solar system, several centimeters, perhaps even meters, of debris may have been deposited on the surface of Iapetus, he said.
The ring is also notable for its unique properties, including its size.
"It's huge," Verbiscer said. "If you could see the ring, it would be the width of two full moons, one moon wide on either side of Saturn."
She added that one would have to stack up a billion Earths to occupy the same amount of volume, and the ring's thickness is equal to that of 20 Saturns stacked on top of each other.
Its radius is 200 to 300 times Saturn's, Skrutskie said, and unlike Saturn's other rings, which rotate equatorially, the ring is tilted at a 27 degree angle.
"The ghostly nature of it is quite interesting," he added. Though the ring is described as smoky, it is actually about a million times lower in optical depth than smoke, he said.
The ring, however, may not entirely solve the age-old mystery, Verbiscer said. She explained that there is a slight difference in color between Iapetus and Phoebe, leading some people to question the theory. Skrutskie suggested that the change in coloration could be attributed to the speed at which debris hits the surface of Iapetus, which might chemically modify the particles.
"The ring has been described as being the smoking gun between those two moons," Verbiscer said. "It's not absolute confirmation or truth that that is what's going on ... [but] it's certainly a very major, major piece of the puzzle."
The discovery was published online in Nature earlier this week, Verbiscer said. The ring will not have a name until the International Astronomical Union officially names it, she said.
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