Images taken by Saturn-bound Cassini spacecraft cameras last Jan. 23 have given planetary scientists first size estimates on asteroid 2685 Masursky and preliminary evidence that it may be different in material properties than previously believed.
"The Masursky images represent the first time that Cassini has gathered information on a body not extensively studied from Earth," said Carolyn C. Porco, leader of the Cassini Imaging Team and associate professor at the University of Arizona Lunar and Planetary Laboratory.
This also was the first time that Cassini's automated object-targeting capabilities have been used and they functioned as expected, Porco added.
Two Cassini images are being released today on the Internet at CICLOPS, the official web site of the Cassini Imaging Science Team, and on NASA Photojournal.
The Cassini spacecraft has been flying towards Jupiter since its swing by Earth for a gravity assist last Aug. 18. It entered the asteroid belt in mid November.
Tolis Christou, a graduate student of Imaging Team member Carl Murray at Queen Mary and Westfield College in London, was the first to realize that the Cassini spacecraft would close in on the little-studied asteroid 2685 Masursky. He and Murray alerted Porco who reported the encounter opportunity to the Cassini Project.
From its location in the solar system, scientists believed Masursky to be similar to several other asteroids visited by spacecraft -- Gaspra, Ida and Eros.
Cassini cameras began taking pictures of the asteroid from seven to 5 and 1/2 hours before closest approach, or a distance of 1.6 million kilometers (960,000 miles), Porco said. Scientists hoped Cassini could help them determine the asteroid's size -- it is too small an object to measure from Earth -- its reflectivity, asteroid category and possibly rotation period.
"So far, the images reveal that the side of Masursky imaged by Cassini is roughly 15 to 20 kilometers (9 to 12 miles) across," Porco said. "Further analysis will hopefully reveal if it is the type of asteroid we think it is. If it isn't, that would be intriguing."
The asteroid belt is a collection of millions of bodies larger than one kilometer (six-tenths' mile) orbiting the sun between Mars and Jupiter. Their origins are not well understood. Some are made of very fresh and pristine material, while others seem certainly to have resided at one time deep in the hot interior of a minor planet, Porco said. It is this ambiguity, and what it implies about the events that occurred in early solar system history, that drives scientists to want to learn as much about them as possible.
The asteroid is named for renowned planetary geologist Harold Masursky (1923-1990), a major participant in the historic Mercury and Apollo planetary exploration programs, the Viking mission to Mars and the Voyager mission to the outer solar system.
The Cassini spacecraft is scheduled to reach its ultimate destination, Saturn, in July 2004. It will then begin an in-depth, 4-year exploration of that planetary system. Cassini's next major maneuver is the December 2000 swing by Jupiter for a final gravity boost towards Saturn.
The Cassini mission is managed by NASA's Jet Propulsion Laboratory in Pasadena, Calif., for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology.
Relevant Web links:
* CICLOPS -- http://ciclops.lpl.arizona.edu
* NASA Photojournal http://photojournal.jpl.nasa.gov
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