- The Washington Times - Friday, July 6, 2007


A NASA probe powered by an ion engine is scheduled to lift off as early as Sunday toward the dwarf planet Ceres, and researchers at the University of Maryland will be watching with interest.

University astronomer Lucy McFadden is a co-investigator and education director for the $449 million project.

“I’m excited, but I don’t want to get too excited until I see the rocket take off,” she told the Baltimore Sun.

NASA had cut the Dawn project last year, citing cost overruns and technical issues, but reversed the decision after an appeal by the Jet Propulsion Laboratory in Pasadena, Calif., which manages the mission.

Powered by a xenon ion engine, Dawn would be the first spacecraft to circle Ceres and Vesta. It will spend several months orbiting each asteroid, photographing the surface and studying the interior composition, density and magnetism.

Ceres and Vesta are thought to have formed in different parts of the solar system about 4.5 billion years ago. Studying them could provide clues to how the sun and planets formed.

A launch scheduled for tomorrow at Cape Canaveral was postponed because of a lightning threat in Florida yesterday, when NASA had planned to begin pumping fuel into its Delta II rocket. The next launch opportunity is 4:04 p.m. Sunday, but a 60 percent chance of bad weather is forecast. Launch windows will be open until July 23.

“It’s been a rocky road, but we’re ready for launch,” Mrs. McFadden said. “I just hope the rains will cease in Florida long enough for us to get off the ground.”

Mrs. McFadden and her colleagues have been studying images of Ceres and Vesta taken by the Hubble Space Telescope in preparation for the mission. The images show a variety of light and dark surface features, and NASA hopes to get close-up images when Dawn orbits Vesta in 2011 and Ceres in 2015.

When Ceres was discovered in 1801, astronomers at first thought it was a new planet. Vesta was discovered in 1807. As more objects were found, astronomers classified the two as part of a region known the “asteroid belt.”

Despite the name, some objects in the belt are fairly large. Ceres, for example, is the size of Texas at 600 miles across and Vesta is 320 miles across.

Last year, the International Astronomical Union reclassified Ceres as a “dwarf planet,” along with Pluto and Eris, an icy object beyond Pluto. The classification means each is large enough that its gravity formed it into a spherical shape, but small enough that it was not able to pull rubble from its orbit.

Mrs. McFadden said Ceres and Vesta appear very different based on telescopic observation and lavalike meteorites thought to have come from Vesta.

“One [Ceres] is water-rich, and the other appears to be dry,” Mrs. McFadden said.

Ceres may be more like the icy moons of the outer planets, while Vesta is more like the rocky inner planets.

“What caused the two bodies to take different paths in their evolution? We want to understand how that relates to the formation of the terrestrial [rocky] planets,” Mrs. McFadden said.

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