Scientists zero in on the origins of Saturns moons

Images of Saturns moons orbiting near he planets outer rings, taken by NASA, have shed light on their rigin.

Washington, Dec 7 : Images of Saturn's moons orbiting near he planet's outer rings, taken by NASA, have shed light on their rigin.

It has long been suspected that Saturn's rings formed in the isintegration of one or several large icy bodies, perhaps pre-xisting moons, by giant impacts.

The resulting debris quickly spread and settled into the quatorial plane to form a thin disk surrounding the planet. And he small, irregularly shaped ring-region moons were believed to e the leftover pieces from this breakup.

Now, several years' worth of images of Saturn's 14 known small oons have been used to derive the sizes and shapes of most of hem, and in about half the cases, even masses and densities.

Evidence for the theory regarding the origin of the moons comes rom the very low density of the inner moons, about half of that f pure water ice, and sizes and shapes that suggest they have rown by the accumulation of ring material.

But the contradiction here is that these moons are within and ear the rings, where it is not possible for small particles to ravitationally fuse together.

"We think the only way these moons could have reached the sizes hey are now, in the ring environment, was to start off with a assive core to which the smaller, more porous ring particles ould easily become bound," said Carolyn Porco, Cassini imaging eam leader from the Space Science Institute in Boulder.

Simple calculations and more complicated computer simulations ave shown that ring particles will readily become bound to a arger seed having the density of water ice. By this process, a oon will grow even if it is relatively close to Saturn. The esult is a ring-region moon about two to three times the size of ts dense ice core, covered with a thick shell of porous, icy ing material."The core may in fact be one of the remnants from the original ing-forming event," said co-author Derek Richardson, professor f astronomy at the University of Maryland, College Park. "It ight have been left intact all this time and protected from dditional collisional breakup by the mantle of ring particles round it," he added."Just exactly when the rings formed is not known. But it is not ut of the question that the moons date back to the time of ring ormation," said Porco.

ANI