Dust particle impacts during the Giotto encounter with comet Grigg–Skjellerup

Abstract

IN the European Space Agency's 1992 Giotto Extended Mission, the Dust Impact Detection System operated successfully during a fly-by that took the spacecraft within about 200 km of the nucleus of comet Grigg–Skjellerup. During the encounter, three meteoroid impacts were detected on Giotto's front shield. The particle masses were found to be lOO⁺¹⁰⁵_-50 µg, 2⁺⁴_-1 µg and 20⁺²⁵_-10 µg, suggesting that the mass distribution of the cometary dust was dominated by larger particles. This is supported by the independent detection of a very large meteoroid (14⁺⁴⁰_-4 mg) by the Giotto Radio-Science Experiment, and is consistent with data over the same mass range from the 1986 encounter with comet Halley. The results indicate a higher rate of mass loss from the nucleus than previously thought, and hence a higher dust-to-gas mass ratio.