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Juno Waves Detection of Dust Impacts Near Jupiter
Journal article   Peer reviewed

Juno Waves Detection of Dust Impacts Near Jupiter

S. -Y. Ye, T. F. Averkamp, W. S. Kurth, M. Brennan, S. Bolton, J. E. P. Connerney and J. L. Joergensen
Journal of geophysical research. Planets, Vol.125(6), e2019JE006367
06/01/2020
DOI: 10.1029/2019JE006367

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Abstract

The Juno spacecraft entered orbit at Jupiter on 5 July 2016. Since then, Juno has orbited Jupiter in high inclination orbits, crossing the ring plane near perijove. During 20 of the first 21 crossings, the Waves instrument detected signals associated with dust impacts. The impact rate profiles show peaks of order 6 s(-1 )around the ring plane with half width at half maximum similar to 2,000-3,000 km. The polarity ratio of the impact signals did not follow the areas of the antennas exposed to dust impacts that change due to the rotation of the spacecraft, suggesting Waves detects impacts on the Juno spacecraft and not just on the Waves antennas. The impact rate profile changed during Perijove 19, when the spacecraft rotation axis was tilted to the south, increasing the area of the solar panels exposed to impacts, indicating that the detected impacts were on the spacecraft body. Grain sizes of order 1 gm are estimated, and the differential size distribution has a slope of -5.1 and with number densities of order 3 x 10(-6) m(-3). Plain Language Summary Once each orbit, Juno passes within a few to several thousand kilometers of Jupiter's cloudtops at low latitudes. These passes carry the spacecraft through Jupiter's ring plane. The radio and plasma wave instrument on Juno called Waves detects voltage spikes when passing through this plane, even though Juno is well below what is thought to be the inner edge of the known ring system. These spikes are due to impacts by micron-sized grains of dust at relative speeds upward of 70 km s(-1). At such speeds, the dust and even a tiny part of the spacecraft are immediately vaporized and heated to a high enough temperature to form a rapidly expanding cloud of electrons and ions. These clouds momentarily disrupt the potential around the spacecraft causing an impulse in the Waves electric sensor. During the first 21 Juno orbits we find peak impact rates of about 6 per second mainly confined to within 2,000-3,000 km of the ring plane. We estimate the size of these grains in the range of microns, about the size of particles in cigarette smoke.
 Physical Sciences Geochemistry & Geophysics Science & Technology

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