Discovery of the dust trail of the Stardust comet sample return mission target:: 81P/Wild 2

We have succeeded in detecting a dust trail along the orbit of the short-period comet 81P/Wild 2, the target of the Stardust mission, which will fly by 81P/Wild 2 in 2004 January. This is the first discovery in optical wavelengths for which an IR counterpart ( such as from IRAS) has not been reported. The detected trail extends from the nucleus to a point 2.degrees3 (0.14 AU) back along the orbit. Its width is 9" (1.4 x 10(4) km) near the nucleus. Based on a comparison between models and the observed properties of the dust trail, it is likely that the trail is composed of dust particles with a diameter of similar to1 mm (corresponding to 0.5 mg in mass). During the flyby phase of the Stardust spacecraft, it is likely that the spacecraft will experience impacts of such large dust particles along the comet's orbit as well as from smaller grains in the cometary coma. With an impact velocity of trail particles of 6.1 km s(-1), the impact fluence of 0.5 mg trail particles onto the Stardust spacecraft will be similar to0.80 day(-1) inside the dust trail. However, the Whipple bumper shields should prevent physical disruption of the spacecraft by impacting particles of up to 1 cm in size. Thus, unless the 1 mm trail dust impacts cause severe attitude control problems for the spacecraft, they may not be critically hazardous to the mission but instead may provide a unique opportunity for the first in situ flux measurement of a comet dust trail, using the Whipple bumper shield dust flux monitors.