The team has received good data from an instrument that studies the three-dimensional distribution of ions and electrons, or plasma, and from an ion engine diagnostic instrument.

The best black-and-white image seen so far is at about 70 minutes prior to closest approach, with the asteroid appearing as just four pixels across. An apparent target-tracking problem appears to have jeopardized further photo return. Whether there are additional photos will be determined over the next 24 hours. Formal downlink sessions end this evening, but follow-up sessions will continue through the early morning.

The ion propulsion engine will be turned on again tomorrow in order to place the spacecraft on track for a possible flyby in January 2001 of Comet Wilson-Harrington as part of an extended mission after the primary mission concludes September 18, 1999. Comet Wilson-Harrington is believed to be either a dormant comet or a "transition object" that is in the process of changing from a comet to an asteroid.

The object has not been observed to behave like a comet -- spewing gas with a coma and tail -- since 1949; it is very unusual for a comet to exhibit this type of change in behavior. The second possible target of an extended mission, Comet Borrelly, is one of the most active comets that regularly visit the inner solar system. Deep Space 1 could fly by Borrelly in September 2001.