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Register a new userThree years of Galileo dust data: II. 1993 to 1995
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Between Jan 1993 and Dec 1995 the Galileo spacecraft traversed interplanetary space between Earth and Jupiter and arrived at Jupiter on 7 Dec 1995. The dust instrument onboard was operating during most of 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 time 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 interplanetary 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 day whose impact directions are compatible with a Jovian origin. Two different populations of dust particles were detected in the Jovian magnetosphere: small stream particles during Galileos approach to the planet and big particles concentrated closer to Jupiter between the Galilean satellites. There is strong evidence that the dust stream particles are orders of magnitude smaller in mass and faster than the instruments calibration, whereas the calibration is valid for the big particles. Because the data transmission rate was 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, information about 2883 particles detected by the dust instrument during Galileos six years journey to Jupiter is now available.
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The Ulysses spacecraft is orbiting the Sun on a highly inclined ellipse ($i = 79^{circ}$). After its Jupiter flyby in 1992 at a heliocentric distance of 5.4 AU, the spacecraft reapproached the inner solar system, flew over the Suns south polar region in September 1994, crossed the ecliptic plane at a distance of 1.3 AU in March 1995, and flew over the Suns north polar region in July 1995. We report on dust impact data obtained with the dust detector onboard Ulysses between January 1993 and December 1995. We publish and analyse the complete data set of 509 recorded impacts of dust particles with masses between $10^{-16}$ g to $10^{-7}$ g. Together with 968 dust impacts from launch until the end of 1992 published earlier (Grun et al., 1995, {em Planet. Space Sci}, Vol. 43, p. 971-999), information about 1477 particles detected with the Ulysses sensor between October 1990 and December 1995 is now available. The impact rate measured between 1993 and 1995 stayed relatively constant at about 0.4 impacts per day and varied by less than a factor of ten. Most of the impacts recorded outside about 3.5 AU are compatible with particles of interstellar origin. Two populations of interplanetary particles have been recognised: big micrometer-sized particles close to the ecliptic plane and small sub-micrometer-sized particles at high ecliptic latitudes. The observed impact rate is compared with a model for the flux of interstellar dust particles which gives relatively good agreement with the observed impact rate. No change in the instruments noise characteristics or degradation of the channeltron could be revealed during the three-year period.
The Ulysses spacecraft has been orbiting the Sun on a highly inclined ellipse since it encountered Jupiter in February 1992. Since then it made almost three revolutions about the Sun. Here we report on the final three years of data taken by the on-board dust detector. During this time, the dust detector recorded 609 dust impacts of particles with masses 10^-16 g <= m <= 10^-7 g, bringing the mission total to 6719 dust data sets. The impact rate varied from a low value of 0.3 per day at high ecliptic latitudes to 1.5 per day in the inner solar system. The impact direction of the majority of impacts between 2005 and 2007 is compatible with particles of interstellar origin, the rest are most likely interplanetary particles. We compare the interstellar dust measurements from 2005/2006 with the data obtained during earlier periods (1993/1994) and (1999/2000) when Ulysses was traversing the same spatial region at southern ecliptic latitudes but the solar cycle was at a different phase. During these three intervals the impact rate of interstellar grains varied by more than a factor of two. Furthermore, in the two earlier periods the grain impact direction was in agreement with the flow direction of the interstellar helium while in 2005/2006 we observed a shift in the approach direction of the grains by approximately 30 deg away from the ecliptic plane. The reason for this shift remains unclear but may be connected with the configuration of the interplanetary magnetic field during solar maximum. We also find that the dust measurements are in agreement with the interplanetary flux model of Staubach et al. (1997) which was developed to fit a 5-year span of Ulysses data.
The Galileo spacecraft was orbiting Jupiter between Dec 1995 and Sep 2003. The Galileo dust detector monitored the jovian dust environment between about 2 and 370 R_J (jovian radius R_J = 71492 km). We present data from the Galileo dust instrument for the period January 2000 to September 2003. We report on the data of 5389 particles measured between 2000 and the end of the mission in 2003. The majority of the 21250 particles for which the full set of measured impact parameters (impact time, impact direction, charge rise times, charge amplitudes, etc.) was transmitted to Earth were tiny grains (about 10 nm in radius), most of them originating from Jupiters innermost Galilean moon Io. Their impact rates frequently exceeded 10 min^-1. Surprisingly large impact rates up to 100 min^-1 occurred in Aug/Sep 2000 when Galileo was at about 280 R_J from Jupiter. This peak in dust emission appears to coincide with strong changes in the release of neutral gas from the Io torus. Strong variability in the Io dust flux was measured on timescales of days to weeks, indicating large variations in the dust release from Io or the Io torus or both on such short timescales. Galileo has detected a large number of bigger micron-sized particles mostly in the region between the Galilean moons. A surprisingly large number of such bigger grains was measured in March 2003 within a 4-day interval when Galileo was outside Jupiters magnetosphere at approximately 350 R_J jovicentric distance. Two passages of Jupiters gossamer rings in 2002 and 2003 provided the first actual comparison of in-situ dust data from a planetary ring with the results inferred from inverting optical images.
The Ulysses spacecraft is orbiting the Sun on a highly inclined ellipse ($ i = 79^{circ}$, perihelion distance 1.3 AU, aphelion distance 5.4 AU). Between January 1996 and December 1999 the spacecraft was beyond 3 AU from the Sun and crossed the ecliptic plane at aphelion in May 1998. In this four-year period 218 dust impacts were recorded with the dust detector on board. We publish and analyse the complete data set of both raw and reduced data for particles with masses $rm 10^{-16} g$ to $rm 10^{-8}$ g. Together with 1477 dust impacts recorded between launch of Ulysses and the end of 1995 published earlier cite{gruen1995c,krueger1999b}, a data set of 1695 dust impacts detected with the Ulysses sensor between October 1990 and December 1999 is now available. The impact rate measured between 1996 and 1999 was relatively constant with about 0.2 impacts per day. The impact direction of the majority of the impacts is compatible with particles of interstellar origin, the rest are most likely interplanetary particles. The observed impact rate is compared with a model for the flux of interstellar dust particles. The flux of particles several micrometers in size is compared with the measurements of the dust instruments on board Pioneer 10 and Pioneer 11 beyond 3 AU (Humes 1980, JGR, 85, 5841--5852, 1980). Between 3 and 5 AU, Pioneer results predict that Ulysses should have seen five times more ($rm sim 10 mu m$ sized) particles than actually detected.
The dust detector system onboard Galileo records dust impacts in circumjovian space since the spacecraft has been injected into a bound orbit about Jupiter in December 1995. This is the sixth in a series of papers dedicated to presenting Galileo and Ulysses dust data. We present data from the Galileo dust instrument for the period January to December 1996 when the spacecraft completed four orbits about Jupiter (G1, G2, C3 and E4). Data were obtained as high resolution realtime science data or recorded data during a time period of 100 days, or via memory read-outs during the remaining times. Because the data transmission rate of the spacecraft is very low, the complete data set (i. e. all parameters measured by the instrument during impact of a dust particle) for only 2% (5353) of all particles detected could be transmitted to Earth; the other particles were only counted. Together with the data for 2883 particles detected during Galileos interplanetary cruise and published earlier, complete data of 8236 particles detected by the Galileo dust instrument from 1989 to 1996 are now available. The majority of particles detected are tiny grains (about 10 nm in radius) originating from Jupiters innermost Galilean moon Io. These grains have been detected throughout the Jovian system and the highest impact rates exceeded $rm 100 min^{-1}$. A small number of grains has been detected in the close vicinity of the Galilean moons Europa, Ganymede and Callisto which belong to impact-generated dust clouds formed by (mostly submicrometer sized) ejecta from the surfaces of the moons (Kruger et al., Nature, 399, 558, 1999). Impacts of submicrometer to micrometer sized grains have been detected thoughout the Jovian system and especially in the region between the Galilean moons.
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