Asteroid Mystery In Deep Space: Siblings Or Parent And Child?

Deep Space 1 flew within an estimated 26 kilometers (16 miles) of asteroid 9969 Braille on July 28. 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 2.2 kilometers (1.3 miles) and its shortest side appears to be 1 kilometer (0.6 miles). 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 500 kilometers (310 miles). 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 Braille is one of the asteroids that drift in and out of Earth's orbit over eons and that it will return to Earth's vicinity within a few thousand years.

The flyby, at 9:46 p.m. PDT on July 28 (04:46 Universal Time July 29), occurred at an estimated distance of 26 kilometers (16 miles), 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. Preliminary results suggest that a combination of the asteroid's highly irregular shape, its orientation relative to the Sun and the camera's response under these unusual conditions are responsible.

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.