The Cassini-Huygens probe, which was launched October 15, 1997, is to start orbiting Saturn on June 30. It passed within 2,068 kilometers (1,285 miles) of the moon Phoebe on Friday, the National Aeronautics and Space Administration said.

Cassini-Huygens is a three-billion-dollar joint mission between NASA and the European Space Agency (ESA).

"What spectacular images. So sharp and clear and showing a great many geological features, large and small," said Carolyn Porco, Cassini Imaging Team leader at the Space Science Institute in Boulder, Colorado.

Phoebe, discovered in 1898 by the American astronomer William Henry Pickering, is 220 kilometers (137 miles) wide and is about 13 million kilometers (8.1 million miles) from Saturn.

"What we are seeing is very neat," said Torrence Johnson, Cassini imaging team member at NASA's Jet Propulsion Laboratory in Pasadena, California.

"Phoebe is a heavily cratered body. We might be seeing one of the chunks from the formation of the solar system, 4.5 billion years ago," Johnson said.

Gerhard Neukum, an imaging team member from Freie University in Berlin, added: "It is very interesting and quite clear that a lot of craters smaller than a kilometer are visible.

"This means, besides the big-ones, lots of projectiles smaller than 100 meters (328 feet) have hit Phoebe."

The origin of the projectiles that slammed on the moon is unknown.

"Looking at those big 50 kilometers (31 miles) craters, one has to wonder whether their impact ejecta might be the other tiny moons that orbit Saturn on paths much like Phoebe's," said Joseph Burns, another team member and professor at Cornell University, Ithaca, New York.

Cassini-Huygens will study Saturn, its rings and principal moons for four years. Once it reaches its destination, the probe will have traveled 3.5 billion kilometers (2.2 billion miles) during its nearly seven-year-old trip to Saturn.

It will have passed 31 of Saturn's moons during the voyage.

On December 25, the Cassini orbiter will release its Huygens probe so it can land three weeks later on Saturn's largest moon, Titan, which has a diameter of more than 5,000 kilometers (3,100 miles). NASA built Cassini, while ESA built Huygens.

SPACE.WIRE