Comet dust tail detection by the Juno spacecraft’s magnetometer investigation

During transit from Earth to Jupiter, NASAs Juno spacecraft carried out scientific measurements along its trajectory, using a subset of its instrument suite. One of the instruments turned on during the journey was the micro Advanced Stellar Compass, part of the MAG investigation. The fully autonomous microASC uses a camera to image the sky for attitude determination, its primary function, but it also logs objects appearing multiple times in the camera FOV that are not found in the instrument’s star catalog. In doing so, it routinely logged the motion of illuminated spallation products evolving from the impacts of interplanetary dust particles (IDPs) on the spacecraft. The system is capable of detection of IDPs with a diameter larger than ~5µm, i.e. particles in the size range responsible for the Zodiacal light. The detection mode was activated just after Juno performed a deep space manoeuver at 2.2AU setting the spacecraft up for a gravity assist from a close Earth flyby, sending Juno on a trajectory to rendezvous with Jupiter. The first leg of the journey, from 2.2AU to 0.8AU and to the Earth flyby, was in the ecliptic plane, whereas the trajectory from Earth to Jupiter rose well above the ecliptic plane. This resulted in measured IDP density profiles both in and above the ecliptic plane. In December 2015, half a year before Jupiter orbit insertion, a conspicuously high rate of dust impacts was detected for a fortnight. A closer analysis showed that Juno happened to pass through the tail of a Jupiter family comet.

We here present the observations of the particle population during the December 2015 event, discuss the dust tail evolution and morphology, and present the implications for the comet’s size and volatility.