Detection and characterisation of icy cavities on the nucleus of comet 67P/Churyumov-Gerasimenko
Résumé
We report on the detection of three icy cavities on the nucleus of comet 67P/Churyumov-Gerasimenko. They were identified on
high-resolution anaglyphs built from images acquired by the OSIRIS instrument aboard the Rosetta spacecraft on 2016 April
9-10. Visually, they appear as bright patches of typically 15 to 30 m across whose large reflectances and spectral slopes in
the visible substantiate the presence of sub-surface water ice. Using a new high-resolution photogrammetric shape model, we
determined the three-dimensional shape of these cavities whose depth ranges from 20 to 47 m. Spectral slopes were interpreted
with models combining water ice and refractory dark material and the water ice abundances in the cavities were found to amount
to a few per cent. The determination of the lifetime of the icy cavities was strongly biased by the availability of appropriate and
favourable observations, but we found evidences of values of up to two years. The icy cavities were found to be connected to jets
well documented in past studies. A thermal model allowed us to track their solar insolation over a large part of the orbit of the
comet and a transitory bright jet on 2015 July 18 was unambiguously linked to the brief illumination of the icy bottom of one of
the cavities. These cavities are likely to be the first potential subsurface access points detected on a cometary nucleus and their
lifetimes suggest that they reveal pristine sub-surface icy layers or pockets rather than recently recondensed water vapor.
Domaines
Planète et Univers [physics]Origine | Fichiers produits par l'(les) auteur(s) |
---|