Models of Rosetta/OSIRIS 67P Dust Coma Phase Function

F. Moreno, D. Guirado, O. Muñoz, I. Bertini, C. Tubiana, C. Güttler, M. Fulle, A. Rotundi, V. Della Corte, S. L. Ivanovski, G. Rinaldi, D. Bockelée-Morvan, V. V. Zakharov, J. Agarwal, S. Mottola, I. Toth, E. Frattin, L. M. Lara, P. J. Gutiérrez, Z. Y. Lin, L. Kolokolova, H. Sierks, G. Naletto, P. L. Lamy, R. Rodrigo, D. Koschny, B. Davidsson, M. A. Barucci, J.-L. Bertaux, D. Bodewits, G. Cremonese, V. Da Deppo, S. Debei, M. De Cecco, J. Deller, S. Fornasier, W.-H. Ip, H. U. Keller, M. Lazzarin, J. J. López-Moreno, F. Marzari, and X. Shi. 2018. Models of Rosetta/OSIRIS 67P Dust Coma Phase Function. Astronomical Journal 156, 5, DOI: 10.3847/1538-3881/aae526

The phase function of the dust coma of comet 67P has been determined from Rosetta/OSIRIS images. This function shows a deep minimum at phase angles near 100 degrees, and a strong backscattering enhancement. These two properties cannot be reproduced by regular models of cometary dust, most of them based on wavelength-sized and randomly oriented aggregate particles. We show, however, that an ensemble of oriented elongated particles of a wide variety of aspect ratios, with radii r greater than or similar to 10 mu m, and whose long axes are perpendicular to the direction of the solar radiation, are capable of reproducing the observed phase function. These particles must be absorbing, with an imaginary part of the refractive index of about 0.1 to match the expected geometric albedo, and with porosity in the 60%-70% range.

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