The opposition effect of 67P/Churyumov–Gerasimenko on post-perihelion Rosetta images

Hasselmann, P. H.; Barucci, M. A.; Fornasier, S.; Feller, C.; Deshapriya, J. D. P.; Fulchignoni, M.; Jost, Bernhard; Sierks, H.; Barbieri, C.; Lamy, P. L.; Rodrigo, R.; Koschny, D.; Rickman, H.; A’Hearn, M.; Bertaux, J.-L.; Bertini, I.; Cremonese, G.; Da Deppo, V.; Davidsson, B.; Debei, S.; ... (2017). The opposition effect of 67P/Churyumov–Gerasimenko on post-perihelion Rosetta images. Monthly notices of the Royal Astronomical Society, 469(Suppl_2), S550-S567. Oxford University Press 10.1093/mnras/stx1834

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High-resolution OSIRIS/Rosetta images of 67P/Churyumov–Gerasimenko acquired on the night run of 2016 April 9–10 show, at large scale, an opposition effect (OE) spot sweeping across Imhotep as the phase angle ranges from 0° to 17°. In this work, we fitted the phase curve of the whole surface imaged as well as three particular features using both the linear–exponential and Hapke models. These features encompass different types of spectral behaviour: a circular mesa, one venous structure and an assemblage of bright spots, going from red to blue colours. Both the Hapke and linear–exponential parameters indicate a stepwise sharpening of the OE from bright spots to circular mesa. Yet a very broad nonlinear phase curve is verified and no sign of sharp OE associated with a coherent-backscattering mechanism is observed. We estimate that the 67P surface is dominated by opaque, desiccated and larger-than-wavelength irregular grains. Veins and bright spots display photometric properties consistent with surfaces becoming slightly brighter as they are enriched by high-albedo ice grains. We also report the estimation of normal albedo for all cometary regions observed throughout the image sequence. Comparison to pre-perihelion results indicates that far better insolation of northern brighter regions, i.e. Hapi, Hathor and Seth, is sufficient to explain mismatches on the photometric parameters. However, metre-scale photometric analysis of the Imhotep–Ash boundary area advocates for mild darkening (<7 per cent) of the surface at local scale.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences

UniBE Contributor:

Jost, Bernhard; Pommerol, Antoine and Thomas, Nicolas

Subjects:

500 Science > 520 Astronomy
600 Technology > 620 Engineering

ISSN:

0035-8711

Publisher:

Oxford University Press

Language:

English

Submitter:

Dora Ursula Zimmerer

Date Deposited:

06 Apr 2018 15:47

Last Modified:

06 Apr 2018 15:47

Publisher DOI:

10.1093/mnras/stx1834

BORIS DOI:

10.7892/boris.107578

URI:

https://boris.unibe.ch/id/eprint/107578

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