Decimetre-scaled spectrophotometric properties of the nucleus of comet 67P/Churyumov–Gerasimenko from OSIRIS observations

Publication date: 
Main author: 
Feller, C.
IAA authors: 
Gutierrez, P.J.; Lara, M.L.; Lopez Moreno, J.J.
C. Feller; S. Fornasier; P. H. Hasselmann; A. Barucci; F. Preusker; F. Scholten; L. Jorda; A. Pommerol; B. Jost; O. Poch; M. R. ElMaary; N. Thomas; I. Belskaya; M. Pajola; H. Sierks; C. Barbieri; P. L. Lamy; D. Koschny; H. Rickman; R. Rodrigo; J. Agarwal; M. A’Hearn; J.-L. Bertaux; I. Bertini; S. Boudreault; G. Cremonese; V. Da Deppo; B. J. R. Davidsson; S. Debei; M. De Cecco; J. DellerM. Fulle; A. Giquel; O. Groussin; P. J. Gutierrez; C. Güttler; M. Hofmann; S. F. Hviid; H. Keller; W.-H. Ip; J. Knollenberg; G. Kovacs; J.-R. Kramm; E. Kührt; M. Küppers; M. L. Lara; M. Lazzarin; C. Leyrat; J. J. Lopez Moreno; F. Marzari; N. Masoumzadeh; S. Mottola; G. Naletto; D. Perna; N. Oklay; X. Shi; C. Tubiana; J.-B. Vincent
Publication type: 
<p>We present the results of the photometric and spectrophotometric properties of the 67P/Churyumov–Gerasimenko nucleus derived with the Optical, Spectroscopic and Infrared Remote Imaging System instrument during the closest fly-by over the comet, which took place on 2015 February 14 at a distance of ∼6&nbsp;km from the surface. Several images covering the 0°–33° phase angle range were acquired, and the spatial resolution achieved was 11&nbsp;cm&nbsp;pixel<sup>−1</sup>. The flown-by region is located on the big lobe of the comet, near the borders of the Ash, Apis and Imhotep regions. Our analysis shows that this region features local heterogeneities at the decimetre scale. We observed difference of reflectance up to 40&nbsp;per&nbsp;cent between bright spots and sombre regions, and spectral slope variations up to 50&nbsp;per&nbsp;cent. The spectral reddening effect observed globally on the comet surface by Fornasier et&nbsp;al. (<a class="link link-ref link-reveal xref-bibr" data-open="bib21">2015</a>) is also observed locally on this region, but with a less steep behaviour. We note that numerous metre-sized boulders, which exhibit a smaller opposition effect, also appear spectrally redder than their surroundings. In this region, we found no evidence linking observed bright spots to exposed water-ice-rich material. We fitted our data set using the Hapke 2008 photometric model. The region overflown is globally as dark as the whole nucleus (geometric albedo of 6.8&nbsp;per&nbsp;cent) and it has a high porosity value in the uppermost layers (86&nbsp;per&nbsp;cent). These results of the photometric analysis at a decimetre scale indicate that the photometric properties of the flown-by region are similar to those previously found for the whole nucleus.</p>
methods: data analysis, space vehicles, space vehicles: instruments, techniques: image processing, techniques: photometric, comets: individual: 67P/Churyumov, Gerasimenko