CICLOPS: Cassini Imaging Central Laboratory for OPerationS

Features On Saturn's Moon Phoebe Named

Preston Dyches (720) 974-5823
CICLOPS/Space Science Institute, Boulder, Colo.

For Immediate Release: February 24, 2005


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, the first stop in the Saturn tour by the Cassini spacecraft taken in June 2004, are being released today and show the names and locations of the 24 craters identified by the Cassini imaging team as prominent enough to receive names.

The new Phoebe images are available at, and

"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 Dr. 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".

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.

"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 Dr. 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 composites being released today.

The practice for the International Astronomical Union is to use a different category 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. They 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, since her legend is rather short and there were not enough names for all the features that required them. Phoebe is named after a Titan goddess, grandmother of Apollo in Greek mythology.

"Since the dawn of exploration, humans have made maps to document where they have been and how to get there. 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" said Dr. 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.

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.

Naming features on planetary bodies is the result of cooperation between the International Astronomical Union, the U.S. Geological Survey, and NASA. The International Astronomical Union is the internationally recognized authority for assigning names to planetary surface features, and the Astrogeology Team of the U.S. Geological Survey in Flagstaff, Ariz., maintains the database containing all planetary feature names (see the Gazetteer of Planetary Nomenclature at
The work performed by the Astrogeology Team is supported by NASA.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.


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