Nasa craft flies by dark moon of Saturn

Phoebe's true nature is revealed in startling clarity in this NASA mosaic of two images released on June 14, 2004, taken during Cassini's flyby on June 11. PHOTO: AFP

Cassini captured data on Phoebe on its way to a four-year orbital mission around the ringed planet, scientists said in a statement. The craft's closest pass to Phoebe took place at 4:56 p.m. EDT on Friday.

Phoebe is a bit of an eccentric among Saturn's 31 known moons, orbiting the planet in the opposite direction from most of the planet's other large satellites, at a 30-degree tilt when compared to Saturn's equatorial plane.

"That means it's really odd," said Bonnie Buratti, who has studied Phoebe for 20 years and is a lead scientist on the Cassini mission.

Last observed from space in images snapped by the Voyager probe in 1981, Phoebe is known to be rough and craggy, so uneven that there may be a huge mountain or crater, Buratti said in a telephone interview from the Jet Propulsion Laboratory in Pasadena, California.

Cassini took pictures from a much closer vantage point -- 1,240 miles as opposed to 1.4 million miles with Voyager -- and shed some light on what Phoebe's uneven surface is made of and where it originated.

Earlier observations indicate that the darkness may indicate the presence of carbon on Phoebe, an important finding since carbon is one of the building blocks of life, Buratti said.

There is also frozen water on Phoebe, another finding of potential interest to astronomers looking for clues to how life came to Earth.

Cassini flew by Phoebe on its way to an orbital path around Saturn. The spacecraft is expected to enter Saturn's orbit on June 30.

The Cassini mission is a joint project of Nasa, the European Space Agency and the Italian Space Agency.