[meteorite-list] Dawn Mission to Vesta Gets Help from Hubble Space Telescope

[Ron Baalke]

Oct. 08, 2010

Dwayne Brown 
Headquarters, Washington 
202-358-1726 
dwayne.c.brown at nasa.gov 

Jia-Rui Cook/D.C. Agle 
Jet Propulsion Laboratory, Pasadena, Calif. 
818-354-0850/393-9011 
jia-rui.c.cook at jpl.nasa.gov/david.c.agle at jpl.nasa.gov 

Ray Villard 
Space Telescope Science Institute, Baltimore 
410-338-4514 
villard at stsci.edu   


RELEASE: 10-254

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   
	
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