NASA Mission to Asteroid Gets Help From Hubble

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Jia-Rui C. Cook/D.C. Agle 818-354-0850/393-9011
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Dwayne Brown 202-358-1726
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Ray Villard 410-338-4514
Space Telescope Science Institute, Baltimore
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NEWS RELEASE: 2010-330 Oct. 8, 2010

NASA Mission to Asteroid Gets Help From Hubble

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-330&cid=release_2010-330

PASADENA, Calif. – NASA's Hubble Space Telescope has captured images of the large asteroid Vesta
that will help refine plans for the Dawn spacecraft's rendezvous with Vesta in July 2011.

Scientists have constructed a video from the images that will help improve pointing instructions for Dawn as it
is placed in a polar orbit around Vesta. Analyses of Hubble images revealed a pole orientation, or tilt, of
approximately four degrees more to the asteroid's east than scientists previously thought.

This means the change of seasons between the southern and northern hemispheres of Vesta may take place
about a month later than previously expected while Dawn is orbiting the asteroid. The result is a change in the
pattern of sunlight expected to illuminate the asteroid. Dawn needs solar illumination for imaging and some
mapping activities.

"While Vesta is the brightest asteroid in the sky, its small size makes it difficult to image from Earth," said
Jian-Yang Li, a scientist participating in the Dawn mission from the University of Maryland in College Park.
"The new Hubble images give Dawn scientists a better sense of how Vesta is spinning, because our new
views are 90 degrees different from our previous images. It's like having a street-level view and adding a
view from an airplane overhead."

The recent images were obtained by Hubble's Wide Field Camera 3 in February. The images complemented
previous ones of Vesta taken from ground-based telescopes and Hubble's Wide Field and Planetary
Camera 2 between 1983 and 2007. Li and his colleagues looked at 216 new images -- and a total of 446
Hubble images overall -- to clarify how Vesta was spinning. The journal Icarus recently published the report
online.

"The new results give us food for thought as we make our way toward Vesta," said
Christopher Russell, Dawn's principal investigator at the University of California, Los Angeles. "Because our
goal is to take pictures of the entire surface and measure the elevation of features over most of the surface to
an accuracy of about 33 feet, or the height of a three-story building, we need to pay close attention to the
solar illumination. It looks as if Vesta is going to have a late northern spring next year, or at least later than
we planned."

Launched in September 2007, Dawn will leave Vesta to encounter the dwarf planet Ceres in 2015. Vesta
and Ceres are the most massive objects in the main asteroid belt between Mars and Jupiter. Scientists study
these celestial bodies as examples of the building blocks of terrestrial planets like Earth. Dawn is
approximately 216 million kilometers (134 million miles) away from Vesta. Next summer, the spacecraft will
make its own measurements of Vesta's rotating surface and allow mission managers to pin down its axis of
spin.

"Vesta was discovered just over 200 years ago, and we are excited now to be on the threshold of exploring
it from orbit," said Bob Mase, Dawn's project manager at NASA's Jet Propulsion Laboratory in Pasadena,
Calif. "We planned this mission to accommodate our imprecise knowledge of Vesta. Ours is a journey of
discovery and, with our ability to adapt, we are looking forward to collecting excellent science data at our
target."

The Dawn mission is managed by JPL, a division of the California Institute of Technology in Pasadena, for
NASA's Science Mission Directorate at the agency's headquarters in Washington. Orbital Sciences
Corporation of Dulles, Va., designed and built the spacecraft. Several international space organizations are
part of the mission team.

To see the Vesta images and video, visit:
http://www.nasa.gov/mission_pages/dawn/multimedia/vestavid20101008.html .

To learn more about Dawn and its mission to the asteroid belt, visit: http://www.nasa.gov/dawn or
http://dawn.jpl.nasa.gov .

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