Radio Doppler data at X band ($8.4 GHz) and spacecraft attitude control data were obtained during the encounter with comet 81P/Wild 2. The Doppler data set an upper bound of 5 Â 10 15 kg on the mass of the nucleus, about 100 times larger than theoretical estimates. The attitude control data indicate that a large dust particle with a mass in the range of 20 to 40 mg impacted the spacecraft about 15.5 s before closest approach.
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