The gas giant may have stripped away a long-lost moon to create its famous rings .

THE GIST

Saturn could have robbed a large but doomed Titan-sized moon of its ice to form the rings.

Measurements taken by NASA's Cassini spacecraft should have solve riddle of how Saturn got its rings.

Rival theories contend the rings formed along with planets or resulted from the smash-up of a comet or inner moon.

Ices stripped off a long-lost moon may have provided the raw materials for Saturn's rings and inner satellites before the Titan-twin slammed into its mother planet, new research shows.

A sophisticated computer model demonstrates how tidal forces on Saturn could have peeled away the icy outer layers of a large moon that occupied an unfortunate piece of real estate. After pulling off the ices, the gravity of Saturn would have doomed the moon's silicate core, tugging it closer and closer until it smashed into the planet, the simulation shows.

The theory neatly accounts for why Saturn's rings are nearly pure ice, while most objects in that part of the solar system are more an ice-rock blend.

Planetary scientist Aurélien Crida, with the Université de Nice Sophia-Antipolis, France, notes that the stripped-off ice would have swirled in rings about 1,000 times more massive than what exist today..

"This elegant model could provide the missing links between a suite of observational and theoretical results that have changed our understanding of Saturn's rings," Crida writes in a review of the research in this week's Nature.

The research may not stay purely theoretical for long. NASA's Saturn-orbiting Cassini spacecraft, which has been studying the planet and its rings and moons since 2004, will spend the last phase of its life orbiting inside the main ring belt.

"We think there is about a 3,000-kilometer-wide (1,864-mile-wide) gap between the planet's atmosphere and the D-ring," Saturn's inner-most ring, Cassini project scientist Linda Spilker, with NASA's Jet Propulsion Laboratory in Pasadena, Calif., told Discovery News.

From that perspective, Cassini would be able to make unprecedented measurements of the rings' density, information that could then be used to refute or buttress the computer model developed by planetary scientist Robin Canup, with the Southwest Research Institute in Boulder, Colo.

Her theory is the latest on how Saturn got its rings, which, in turn, are believed to have formed the inner moons. Other hypotheses: The rings are the remains of a inner moon that was struck by a meteor or other object; The rings formed from the remains of a destroyed comet; The rings formed at the same time as Saturn and the other planets in the solar system.

Knowing how much material is in the rings will be a significant step to figuring out the puzzle, Spilker said.

"Cassini will be able to measure the mass of the rings to a few percent," added NASA planetary scientist Jeff Cuzzi, with the Ames Research Center in Moffett Field, Calif. "There will be no question about the mass of the rings. We will know."

Canup's research appears in this week's Nature.