Probe sheds light on Saturn’s dark moon

A SPACECRAFT heading for Saturn has returned the first close-up pictures of the planet’s oddball moon, Phoebe.

The images sent back by the Cassini probe reveal a surface heavily potholed with craters and scarred by linear structures such as grooves, ridges and chains of pits.

Bright streaks and rays can be seen in and around craters, indicating the presence of ice.

Phoebe, which is about 220 kilometres in diameter, is unusual in that it orbits in the opposite direction from Saturn’s other moons.

Scientists had speculated that it might be a captured asteroid or a comet-like body dragged from the outer limits of the solar system when Saturn was forming.

The new data seem to be lending weight to the theory that Phoebe began life in the distant Kuiper Belt, the home of icy comets.

Dr Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, Colorado, US, said: “The imaging team is in hot debate at the moment on the interpretations of our findings.

“Based on our images, some of us are leaning towards the view that has been promoted recently, that Phoebe is probably ice-rich and may be an object originating in the outer solar system, more related to comets and Kuiper Belt objects than to asteroids.”

“This has been an impressive whirlwind fly-by and it’s only a curtain-raiser on the events about to begin,” said Dr Porco.

The truck-sized probe is the first man-made object to orbit Saturn. Over the next four years, Cassini will execute 52 close encounters with seven of Saturn’s 31 known moons and gather data on the planet, its rings and magnetic environment. On December 25, a wok-shaped probe, Huygens, will land by parachute on the largest moon, Titan.