Interpretation through experimental simulations of phase functions revealed by Rosetta in 67P/Churyumov-Gerasimenko dust coma

¹ LATMOS, Sorbonne Université, CNRS, UVSQ, Campus Pierre et Marie Curie, 4 place Jussieu, 75005 Paris, France
e-mail: aclr@latmos.ipsl.fr
² LPC2E-CNRS, 3A avenue de la Recherche Scientifique, 45071 Orléans cedex 2, France
³ LATMOS/IPSL, UVSQ Université Paris-Saclay, Sorbonne Université, CNRS, Guyancourt, France
⁴ IRAP, Université de Toulouse, CNRS, CNES, UPS, 9 avenue Colonel Roche, 31400 Toulouse, France
⁵ Department of Physics and Astronomy G. Galilei, University of Padova, Vic. Osservatorio 3, 35122 Padova, Italy
⁶ INAF – Osservatorio Astronomico, Via Tiepolo 11, 34143 Trieste, Italy

Received: 16 December 2018
Accepted: 5 March 2019

Abstract

Context. The dust-brightness phase curves that have been measured by the OSIRIS cameras on board the Rosetta spacecraft within the coma of comet 67P/Churyumov-Gerasimenko (67P) present a remarkable flattened u-shape.

Aims. Our goal is to compare these phase curves with those of tentatively analog dust samples to assess the key dust properties that might induce this shape.

Methods. Light-scattering measurements have been made with the PROGRA2 instrument in the laboratory and in microgravity conditions on samples of different physical properties and compositions that are likely to be representative of cometary dust particles.

Results. We find that the brightness phase curves of a series of interplanetary dust analogs that have been recently developed (to fit the polarimetric properties of the inner zodiacal cloud and their changes with heliocentric distance) are quite comparable to those of 67P. Key dust properties seem to be related to the composition and the porosity.

Conclusions. We conclude that the shape of the brightness phase curves of 67P has to be related to the presence of a significant amount of organic compounds (at least 50% in mass) and of fluffy aggregates (of a size range of 10–200 μm). We also confirm similarities between the dust particles of this Jupiter-family comet and the particles within the inner zodiacal cloud.