The Stardust spacecraft, which will collect particles from Comet Wild 2 and parachute them back to the Earth, just got some target practice. On November 2nd the spacecraft used a close approach to minor planet 5535 Annefrank for a systems-operations test that included imaging the asteroid from a distance of 3,300 kilometers. "It turns out to be a tremendous plus, because you end up having a full dress rehearsal more than a year ahead of the encounter," says Donald Brownlee, the mission's principal investigator.
Zooming by at 7 km per second, Stardust looked over Annefrank for a half hour. The rather distant flyby was intentional, notes Thomas Duxbury, Stardust's project manager, because "in the event that Annefrank had dust or satellites we didn't want to get too close." Despite the expectation of a dust-free encounter, the spacecraft deployed its dust collector and dust-analyzing mass spectrometer in addition to its camera "so that the flyby would be a thoroughly valid test," Duxbury says.
Seventy images were acquired at resolutions down to 200 meters per pixel, and half of these were radioed to Earth within 48 hours. The others will be relayed next Saturday. So far it appears that Annefrank has a highly irregular shape and a cratered, variegated surface. The dust-flux and mass-spectrometer data, which Duxbury says show "a few potential unexplained results," are being analyzed at the University of Chicago and the Max Planck Institute in Germany.
Plans call for the Stardust spacecraft to fly within 100 km of Wild 2 on January 2, 2004, in order to record the closest-ever pictures of a comet's nucleus. But its primary mission is to collect particles streaming off the comet's nucleus. These tiny samples will be returned back to Earth in the hope that they can answer key questions about our solar system's formation 4½ billion years ago.
Two forthcoming missions will complement Stardust's mad dash. After launch next January, the European Space Agency's Rosetta spacecraft will head to Comet 46/P Wirtanen and release a lander on the icy body in order to collect samples during a 2-year rendezvous beginning in November of 2011. NASA's Deep Impact mission, to be launched in February 2004, will slam a 370-kilogram projectile into Comet 9P/Temple 1 in order to study cometary cratering and natural outgassing in July of 2005. NASA managers have not yet decided whether to rebuild its Contour comet-chaser, which was lost in August.