GIADA microbalance measurements on board Rosetta: submicrometer- to micrometer-sized dust particle flux in the coma of comet 67P/Churyumov-Gerasimenko

¹ Institute of Astrophysics and Planetology (IAPS), INAF, via del Fosso del Cavaliere, 100, 00133 Roma, Italy
e-mail: vincenzo.dellacorte@iaps.inaf.it
² Department of Sciences and Technologies, University of Naples Parthenope, CDN, IC4, 80143 Napoli, Italy
³ Osservatorio Astronomico di Trieste, INAF, via Tiepolo 11, 34143 Trieste, Italy
⁴ Italian Space Agency, ASI, via del Politecnico Roma, Italy

Received: 16 December 2018
Accepted: 14 June 2019

Abstract

Context. From August 2014 to September 2016, Rosetta escorted comet 67P/Churyumov-Gerasimenko (67P) during its journey around the Sun. One of the aims of Rosetta was to characterize cometary activity and the consequent formation of dust flux structures in cometary comae.

Aims. We characterize and quantify the submicrometer- to micrometer-sized dust flux that may be shaped in privileged directions within the coma of 67P inbound to and outbound from perihelion.

Methods. The in situ dust-measuring instrument GIADA, part of the Rosetta/ESA payload, consisted of three subsystems, one of which was the Micro Balance Subsystem (MBS), composed of five quartz crystal microbalances. From May 2014 to September 2016, MBS measured the submicrometer- to micrometer-sized deposited dust mass every 5 min.

Results. We characterized the submicrometer- to micrometer-sized dust mass flux in the coma of 67P. The anti-sunward and the radial direction are preferred, and the flux is higher in the anti-sunward direction. The measured cumulative dust mass in the anti-sunward direction is 2.38 ± 0.04 × 10⁻⁷ kg, and in the radial direction, it is 1.18 ± 0.02 × 10⁻⁷ kg. We explain the anti-sunward dust flux as the effect of nonuniform gas emission between the night- and dayside of the nucleus, which acts in combination with the solar radiation pressure. We compared the cumulated dust mass of particles ≤5 μm with particles ≥100 μm. The retrieved ratio of ≈2% implies a differential size distribution index of ≈−3.0, which confirms that particles of size ≥0.1 mm dominate the dust coma cross-section of 67P during the entire orbit.

Conclusions. Submicrometer- to micrometer-sized dust mass flux measurements were made for the first time from the arising of cometary activity until its extinction. They indicate that these particles do not provide a substantial optical scattering in the coma of 67P with respect to the scattering caused by millimeter-sized particles. In addition, MBS data reveal that the measured dust flux is highly anisotropic: anti-sunward plus radial.