Twenty-four of the largest craters on Phoebe, the small, retrograde outer moon of Saturn have been assigned names by the International Astronomical Union.

Two image montages of Phoebe, taken in June 2004 on Cassini's first stop on its tour of Saturn, have been released and show the names and locations of the 24 craters identified by the Cassini imaging team as prominent enough to receive names.

The International Astronomical Union, the international authority for assigning names to planetary surface features, makes use of different naming categories for surface features on each object. That way, when people hear or see a name, they can associate it with the object on which the feature is found. The IAU often start with names associated with the legends involving the being whose name is given to the object itself, then choose an additional category if more names are needed.

This is what happened with Phoebe, a Titan goddess and Apollo's grandmother in Greek mythology. Since her legend is rather short, there were not enough names for all the features that required them.

"We picked the legend of the Argonauts for Phoebe as it has some resonance with the exploration of the Saturn system by Cassini-Huygens," said Toby Owen, of the University of Hawaii at Manoa. He is the chairman of the International Astronomical Union Outer Solar System Task Group and an interdisciplinary scientist on the Cassini-Huygens mission.

"We can't say that our participating scientists include heroes like Hercules and Atalanta, but they do represent a wide, international spectrum of outstanding people who were willing to take the risk of joining this voyage to a distant realm in hopes of bringing back a grand prize," said Owen.

"Considering the length and complexity of the Cassini mission, it is appropriate that the names of these courageous voyagers from one of our favorite myths have been used for the first Cassini maps of the Saturn system," said Peter Thomas, Cassini imaging team member, Cornell University, Ithaca, N.Y. and one of the imaging scientists who identified the craters requiring names and created the image montages.

Phoebe is an icy, ancient remnant of the small bodies that formed over four billion years ago in the outer reaches of the solar system. It must have been captured by giant Saturn in the planet's earliest, formative years.

Images collected during Cassini's close flyby of Phoebe have yielded strong evidence that the tiny object may contain ice-rich material overlain with a thin layer of darker material perhaps 300 to 500 meters (980 to 1,600 feet) thick. The surface of Phoebe is also heavily potholed with large and small craters. Images reveal bright streaks in the ramparts of the largest craters, bright rays which emanate from smaller craters and uninterrupted grooves across the face of the body. Phoebe's craters are thought to be the result of collisions with smaller objects.

"Since the dawn of exploration, humans have made maps to document where they have been and how to get there," said Torrence Johnson, Cassini imaging team member at NASA's Jet Propulsion Laboratory, Pasadena, Calif., who coordinated the naming of the Phoebe craters with the IAU. "Having names for the places on the map is an essential part of this process. With the assignment of names to craters on its surface, Phoebe now joins the ranks of charted worlds."