Dust Measurements near Ganymede

Details Dust Measurements near Ganymede Dust Measurements near Ganymede

Sep 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.0114g&link_type=abstract

American Astronomical Society, DPS meeting #28, #01.14; Bulletin of the American Astronomical Society, Vol. 28, p.1055

Astronomy and Astrophysics

Astronomy

Scientific paper

Dust measurements were obtained by the Dust Detector System (DDS) onboard Galileo for 8 days centered around Ganymede closest approach on 27 June 1996. During this period, the DDS instrument was operated in its most sensitive mode just as in interplanetary space. The dust impact rate (for our ``best'' class of impacts, class 3) varied by up to a factor of several hundred over periods as short as a few hours. Maximum rates of about five impact events per minute were recorded on June 25 and at Ganymede closest approach on June 27. If we also include the less reliable class 2 dust impacts, the maximum rate increases by a factor of ~ 3. Significant structure is evident in a plot of impact rate versus time. Three strong bursts, each lasting ~ 5 hours and separated by ~ 10 hours, were observed between June 24 and 26. The first of these burst was the strongest, with subsequent bursts weakening as the spacecraft moved inward towards Jupiter. We also tentatively identify two weak additional bursts, which occurred 10 hours before and after the train of three large bursts. All of these features are visible in both our class 3 and class 2 data sets. The ten-hour periodicity is compatible with Jupiter's rotation period and implies that jovian dust particles are strongly influenced by the planet's magnetic field. In addition to periodic peaks, a very sharp narrow spike lasting only about 5 min. occurred during Ganymede closest approach. The sharpness of the peak points to a Ganymede origin, and we speculate that we are seeing submicron grains ejected by impacts of micrometeoroids with Ganymede. The DDS instrument also measures impact directions, impact velocities, and dust masses. A relatively gradual change in the direction from which dust grains are observed occurred about 1 day before Ganymede closest approach. This directional information gives important clues for the origin of the dust, and will be analyzed by combining the accurate position and pointing of the dust instrument with careful modelling of dust trajectories. The velocity and mass data have yet to be fully analyzed.

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