|Phoebe shape like planet almost spherical (NASA)|
- NASA Found Phoebe Has Planet-Like Qualities
Friday, April 27, 2012
The data obtained from NASA's Cassini revealed that Phoebe (moon of Saturn) has more planet-like qualities than previously thought by scientists. At first they did close-ups of Phoebe when Cassini crossed Saturn system in 2004.
"Unlike primitive bodies such as comets, Phoebe appears to have actively evolved for a time before it stalled out," said Julie Castillo-Rogez, a planetary scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. "Objects like Phoebe are thought to have condensed very quickly. Hence, they represent building blocks of planets. They give scientists clues about what conditions were like around the time of the birth of giant planets and their moons"
Cassini images suggest Phoebe originated in the far-off Kuiper Belt, the region of ancient, icy, rocky bodies beyond Neptune's orbit. Data show Phoebe was spherical and hot early in its history, and has denser rock-rich material concentrated near its center. Its average density is about the same as Pluto, another object in the Kuiper Belt. Phoebe likely was captured by Saturn's gravity when it somehow got close to the giant planet.
Saturn is surrounded by a cloud of irregular moons that circle the planet in orbits tilted from Saturn's orbit around the sun, the so-called equatorial plane. Phoebe is the largest of these irregular moons and also has the distinction of orbiting backward in relation to the other moons. By comparison, Saturn's large moons appear to have formed from gas and dust around the planet's equatorial plane and orbit in that same plane.
"By combining Cassini data with modeling techniques previously applied to other solar system bodies, we've been able to go back in time and clarify why Phoebe is so different from the rest of the Saturn system," said Jonathan Lunine, a co-author on the study and a Cassini team member at Cornell University.
Phoebe likely stayed warm for tens of millions of years before freezing up. The study suggests the heat also would have enabled the moon to host liquid water at one time. This could explain the signature of water-rich material on Phoebe's surface previously detected by Cassini.
The new study also is consistent with the idea that several hundred million years after Phoebe cooled, the moon drifted toward the inner solar system in a solar-system-wide rearrangement. Phoebe was large enough to survive this turbulence.
More than 60 moons are known to orbit Saturn, varying drastically in shape, size, surface age and origin. Scientists using both ground-based observatories and Cassini's cameras continue to search for others.
This story has edited by author of threelas