Unraveling the Enigma of Saturnâ€™s Huge, Ghostly Halo
J Thoendell stashed this in Space
Rings around planets are supposed to stay close to home, as any Astro 101 textbook will tell you. Once they venture too far afield from their gravitational overlord, conventional astronomical wisdom dictates that they will collapse and form new satellites.
â€śThat does a really good job of explaining ringsâ€”except for this one,â€ť says Douglas Hamilton, an astrophysicist at the University of Maryland. Hamilton and colleagues describe Saturnâ€™s biggest, strangest, most recently-discovered ring in a study published today in Nature.Â The so-called Phoebe ring isÂ not only bigger than the researchersÂ thought, it appears to be made of unusually fine particlesâ€”particles that continually collide with Saturnâ€™s moon Iapetus as it circles the planet, turningÂ the moonâ€™s leading face black.
Stashed in: Space!
â€śYou can imagine something big smashed into Phoebe a billion years ago, and all of this debris was flung out,â€ť Hamilton says. When he calculated how long it would take for this debris to be cleaned up (either by collapsing into a new satellite or to fall to Saturn) he found that it would take a shockingly long time: about 10 billion years. Thatâ€™s longer than the solar system has existed. â€śWe realized that all of the debris coating the face of Iapetus, that didnâ€™t happen long ago. Itâ€™s going on now,â€ť he says. So his team started searching for the source of the material painting the moon black. â€śFinding it was really gratifying.â€ť
That was six years ago. Back then, when his team first wrote about theirÂ findings, the only available data on this vanishingly faint ring came in the form of a small cross-section. For Hamilton the picture felt â€śnot much bigger than a postage stamp.â€ťÂ Now, using data from NASAâ€™sÂ Wide-field Infrared Survey ExplorerÂ spacecraft launched in 2009, theyâ€™ve gathered a complete view of Phoebeâ€™s enormous ring. â€śIt was immense beforehand, and we just made it even bigger,â€ť Hamilton says.