Douglas Isbell
Headquarters, Washington DC                      Aug. 5, 1999
(Phone:  202/358-1753)

John G. Watson
Jet Propulsion Laboratory, Pasadena, CA
(Phone:  818/354-5011)

RELEASE:  99-88

ASTEROID MYSTERY IN DEEP SPACE:  SIBLINGS, OR PARENT AND CHILD?

     NASA's novel Deep Space 1 spacecraft not only passed a 
technology milestone when it successful flew itself past an 
asteroid last week, it gave scientists a deep-space "family tree" 
mystery to ponder.

     Deep Space 1 flew within an estimated 16 miles (26 kilometers) 
of asteroid 9969 Braille on July 29. The spacecraft's infrared 
sensor confirmed that the small asteroid is similar to Vesta, a 
rare type of asteroid and one of the largest bodies in the main 
asteroid belt, which lies between Mars and Jupiter.

     "This clear link between Vesta and Braille is an important 
finding," said Dr. Laurence Soderblom of the U.S. Geological 
Survey, team leader for Deep Space 1 experiments using the 
spacecraft's integrated spectrometer and imaging instrument.  

     Scientists are now wrestling with a thorny question:  Is the 
near-Earth asteroid Braille a chip off Vesta's old block, or are 
the two asteroids siblings which originated elsewhere, perhaps 
thrown off a larger body that has long since been destroyed?

     The scientists made their finding from three sets of data 
collected by the spacecraft's infrared camera.  Called spectra -- 
data obtained when the instrument breaks light into component 
colors, much like a prism does -- the data sets cover different 
parts of the asteroid and were taken just after closest approach.

     Braille's longest side is now estimated at 1.3 miles (2.2 
kilometers) and its shortest side appears to be 0.6 miles (1 
kilometer). This elongated asteroid was expected to be irregular, 
and two photographs taken approximately 15 minutes after closest 
encounter have helped to confirm this. 

     By contrast, Vesta, discovered in 1807, has a diameter of 
about 310 miles (500 kilometers). The fourth asteroid ever 
discovered, Vesta shares with Braille a high visual reflectivity.  
In fact, Vesta is the most reflective of the main-belt asteroids. 

     Apart from flyby findings, project scientists have determined 
that in about 4,000 years Braille will join the hundreds of other 
asteroids that drift in and out of Earth's orbit.

     The flyby, at 12:46 am EDT on July 29, occurred at an 
estimated distance of 16 miles (26 kilometers), although the exact 
distance is still being measured. Diagnosis of an apparent target-
tracking problem that affected the taking of black-and-white photos 
during the flyby continues. 

     Launched Oct. 24, 1998, Deep Space 1 is the first mission 
under NASA's New Millennium Program, which tests new technologies 
for future space and Earth-observing missions. The technologies 
that have been tested on Deep Space 1 will help make future science 
spacecraft smaller, less expensive and capable of more independent 
decision-making so that they rely less on tracking and intervention 
by ground controllers. 

     Of the 12 new technologies on board, all but the spacecraft's 
autonomous navigation system had been completely tested since 
launch. With the asteroid encounter, AutoNav successfully finished 
its last 5 percent of testing. Science return was a bonus for this 
technology validation mission.

     A Deep Space 1 asteroid flyby press kit, along with mission 
status reports from launch to the present, is available at:

               http://www.jpl.nasa.gov/ds1news

     The mission is managed for the Office of Space Science, NASA 
Headquarters, Washington, DC, by NASA's Jet Propulsion Laboratory, 
Pasadena, CA, a division of the California Institute of Technology.