NASA Mission To Asteroid Gets Help From Hubble Space Telescope
WASHINGTON -- NASA's Hubble Space Telescope has captured images of the
large asteroid Vesta that will help scientists 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 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 (JPL) 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 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
Source: NASA
