Three years of Galileo dust data: II. 1993-1995

Between January 1993-December 1995, the Galileo spacecraft traversed interp lanetary space between Earth and Jupiter and arrived at Jupiter on 7 Decemb er 1995. The dust instrument onboard the spacecraft was operating during mo st of the time and data from the instrument were obtained via memory readou ts which occurred at rates between twice per day and once per week. All eve nts were classified by an onboard program into 24 categories. Noise events were usually restricted to the lowest categories (class 0). During Galileo' s passage through Jupiter's radiation belts on 7 December 1995, several of the higher categories (classes 1 and 2) also show evidence for contaminatio n by noise. The highest categories (class 3) were noise-free all the time. A relatively constant impact rate of interplanetary and interstellar (big) particles of 0.4 impacts per day was detected over the whole three-year tim e span. In the outer solar system (outside about 2.6 AU) they are mostly of interstellar origin, whereas in the inner solar system they are mostly int erplanetary particles. Within about 1.7 AU from Jupiter intense streams of small dust particles were detected with impact rates of up to 20,000 per da y whose impact directions are compatible with a Jovian origin. Two differen t populations of dust particles were detected in Jovian magnetosphere: smal l stream particles during Galileo's approach to the planet and big particle s concentrated closer to Jupiter between the Galilean satellites. There is strong evidence that the dust stream particles are orders of magnitude smal ler in mass and faster than the instrument's calibration, whereas the calib ration is valid for the big particles. Because the data transmission rate w as very low, the complete data set for only a small fraction (2525) of all detected particles could be transmitted to Earth; the other particles were only counted. Together with the 358 particles published earlier, informatio n about 2883 particles detected by the dust instrument during Galileo's six years' journey to Jupiter is now available. (C) 1999 Elsevier Science Ltd. All rights reserved.