Large heterogeneities in comet 67P as revealed by active pits from sinkhole collapse

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Jean-Baptiste Vincent Dennis Bodewits Sébastien Besse Holger Sierks Cesare Barbieri Philippe Lamy Rafael Rodrigo Detlef Koschny Hans Rickman Horst Uwe Keller Jessica Agarwal Michael F. A’Hearn Anne-Thérèse Auger M. Antonella Barucci Jean-Loup Bertaux Ivano Bertini Claire Capanna Gabriele Cremonese Vania Da Deppo Björn Davidsson Stefano Debei Mariolino De Cecco Mohamed Ramy El-Maarry Francesca Ferri Sonia Fornasier Marco Fulle Robert Gaskell Lorenza Giacomini Olivier Groussin Aurélie Guilbert-Lepoutre P. Gutierrez-Marques Pedro J. Gutiérrez Carsten Güttler Nick Hoekzema Sebastian Höfner Stubbe F. Hviid Wing-Huen Ip Laurent Jorda Jörg Knollenberg Gabor Kovacs Rainer Kramm Ekkehard Kührt Michael Küppers Fiorangela La Forgia Luisa M. Lara Monica Lazzarin Vicky Lee Cédric Leyrat Zhong-Yi Lin Josè J. Lopez Moreno Stephen Lowry Sara Magrin Lucie Maquet Simone Marchi Francesco Marzari Matteo Massironi Harald Michalik Richard Moissl Stefano Mottola Giampiero Naletto Nilda Oklay Maurizio Pajola Frank Preusker Frank Scholten Nicolas Thomas Imre Toth Cecilia Tubiana

Nature 523 , 63–66 (02 July 2015)
doi:10.1038/nature14564

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Pits have been observed on many cometary nuclei mapped by spacecraft1, 2, 3, 4. It has been argued that cometary pits are a signature of endogenic activity, rather than impact craters such as those on planetary and asteroid surfaces. Impact experiments5, 6 and models7, 8 cannot reproduce the shapes of most of the observed cometary pits, and the predicted collision rates imply that few of the pits are related to impacts8, 9. Alternative mechanisms like explosive activity10 have been suggested, but the driving process remains unknown. Here we report that pits on comet 67P/Churyumov–Gerasimenko are active, and probably created by a sinkhole process, possibly accompanied by outbursts. We argue that after formation, pits expand slowly in diameter, owing to sublimation-driven retreat of the walls. Therefore, pits characterize how eroded the surface is: a fresh cometary surface will have a ragged structure with many pits, while an evolved surface will look smoother. The size and spatial distribution of pits imply that large heterogeneities exist in the physical, structural or compositional properties of the first few hundred metres below the current nucleus surface.

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