title: Rosetta's comet 67P/Churyumov-Gerasimenko sheds its dusty mantle to reveal its icy nature.
abstract: The Rosetta spacecraft has investigated comet 67P/Churyumov-Gerasimenko from large heliocentric distances to its perihelion passage and beyond. We trace the seasonal and diurnal evolution of the colors of the 67P nucleus, finding changes driven by sublimation and recondensation of water ice. The whole nucleus became relatively bluer near perihelion, as increasing activity removed the surface dust, implying that water ice is widespread underneath the surface. We identified large (1500 square meters) ice-rich patches appearing and then vanishing in about 10 days, indicating small-scale heterogeneities on the nucleus. Thin frosts sublimating in a few minutes are observed close to receding shadows, and rapid variations in color are seen on extended areas close to the terminator. These cyclic processes are widespread and lead to continuously, slightly varying surface properties.
authors.affiliation: Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique (LESIA), Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, Sorbonne Paris Cité, UPMC Université Paris 06, Sorbonne Universités, 5 Place J. Janssen, Meudon Principal Cedex 92195, France. sonia.fornasier@obspm.fr.
authors.forename: S
authors.initials: S
authors.lastname: Fornasier
authors.affiliation: Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Asteroiden und Kometen, Rutherfordstraﬂe 2, 12489 Berlin, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Mottola
authors.affiliation: Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Asteroiden und Kometen, Rutherfordstraﬂe 2, 12489 Berlin, Germany.|Institut für Geophysik und Extraterrestrische Physik (IGEP), Technische Universität Braunschweig, Mendelssohnstrasse 3, 38106 Braunschweig, Germany.
authors.forename: H U
authors.initials: HU
authors.lastname: Keller
authors.affiliation: Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique (LESIA), Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, Sorbonne Paris Cité, UPMC Université Paris 06, Sorbonne Universités, 5 Place J. Janssen, Meudon Principal Cedex 92195, France.
authors.forename: M A
authors.initials: MA
authors.lastname: Barucci
authors.affiliation: Jet Propulsion Laboratory, M/S 183-301, 4800 Oak Grove Drive, Pasadena, CA 91109, USA.
authors.forename: B
authors.initials: B
authors.lastname: Davidsson
authors.affiliation: Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique (LESIA), Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, Sorbonne Paris Cité, UPMC Université Paris 06, Sorbonne Universités, 5 Place J. Janssen, Meudon Principal Cedex 92195, France.
authors.forename: C
authors.initials: C
authors.lastname: Feller
authors.affiliation: Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique (LESIA), Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, Sorbonne Paris Cité, UPMC Université Paris 06, Sorbonne Universités, 5 Place J. Janssen, Meudon Principal Cedex 92195, France.
authors.forename: J D P
authors.initials: JD
authors.lastname: Deshapriya
authors.affiliation: Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, 3, 37077, Göttingen, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Sierks
authors.affiliation: Department of Physics and Astronomy, University of Padova, Vicolo dell'Osservatorio 3, 35122 Padova, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Barbieri
authors.affiliation: Laboratoire d'Astrophysique de Marseille, UMR 7326 CNRS and Université Aix-Marseille, 38 Rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France.
authors.forename: P L
authors.initials: PL
authors.lastname: Lamy
authors.affiliation: Instituto de Astrofisica de Andalucia (CSIC), c/ Glorieta de la Astronomia s/n, 18008 Granada, Spain.|International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland.
authors.forename: R
authors.initials: R
authors.lastname: Rodrigo
authors.affiliation: Scientific Support Office, European Space Research and Technology Centre/ESA, Keplerlaan 1, Postbus 299, 2201 AZ Noordwijk ZH, Netherlands.
authors.forename: D
authors.initials: D
authors.lastname: Koschny
authors.affiliation: Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden.|Polish Academy of Sciences, Space Research Center, Bartycka 18A, 00716 Warszawa, Poland.
authors.forename: H
authors.initials: H
authors.lastname: Rickman
authors.affiliation: Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA.
authors.forename: M
authors.initials: M
authors.lastname: A'Hearn
authors.affiliation: Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, 3, 37077, Göttingen, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Agarwal
authors.affiliation: Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS) CNRS/UVSQ/IPSL, 11 Boulevard d'Alembert, 78280, Guyancourt, France.
authors.forename: J-L
authors.initials: JL
authors.lastname: Bertaux
authors.affiliation: Department of Physics and Astronomy, University of Padova, Vicolo dell'Osservatorio 3, 35122 Padova, Italy.
authors.forename: I
authors.initials: I
authors.lastname: Bertini
authors.affiliation: Operations Department, European Space Astronomy Centre/ESA, P.O. Box 78, 28691 Villanueva de la Canada, Madrid, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Besse
authors.affiliation: Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Cremonese
authors.affiliation: CNR-IFN UOS Padova LUXOR, Via Trasea, 7, 35131 Padova, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Da Deppo
authors.affiliation: Department of Mechanical Engineering - University of Padova, via Venezia 1, 35131 Padova, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Debei
authors.affiliation: University of Trento, Via Mesiano 77, 38100 Trento, Italy.
authors.forename: M
authors.initials: M
authors.lastname: De Cecco
authors.affiliation: Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, 3, 37077, Göttingen, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Deller
authors.affiliation: Physikalisches Institut der Universität Bern, Sidlerstrasse 5, 3012 Bern, Switzerland.
authors.forename: M R
authors.initials: MR
authors.lastname: El-Maarry
authors.affiliation: INAF, Osservatorio Astronomico, Via Tiepolo 11, 34014 Trieste, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Fulle
authors.affiliation: Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille), UMR 7326, 38 Rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France.
authors.forename: O
authors.initials: O
authors.lastname: Groussin
authors.affiliation: Instituto de Astrofisica de Andalucia (CSIC), c/ Glorieta de la Astronomia s/n, 18008 Granada, Spain.
authors.forename: P J
authors.initials: PJ
authors.lastname: Gutierrez
authors.affiliation: Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, 3, 37077, Göttingen, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Güttler
authors.affiliation: Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, 3, 37077, Göttingen, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Hofmann
authors.affiliation: Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Asteroiden und Kometen, Rutherfordstraﬂe 2, 12489 Berlin, Germany.
authors.forename: S F
authors.initials: SF
authors.lastname: Hviid
authors.affiliation: Graduate Institute of Astronomy, National Central University, 300 Chung-Da Rd, Chung-Li 32054 Taiwan.|Space Science Institute, Macau University of Science and Technology, Macau, China.
authors.forename: W-H
authors.initials: WH
authors.lastname: Ip
authors.affiliation: Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille), UMR 7326, 38 Rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France.
authors.forename: L
authors.initials: L
authors.lastname: Jorda
authors.affiliation: Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Asteroiden und Kometen, Rutherfordstraﬂe 2, 12489 Berlin, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Knollenberg
authors.affiliation: Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, 3, 37077, Göttingen, Germany.|Budapest University of Technology and Economics, Budapest, Hungary.
authors.forename: G
authors.initials: G
authors.lastname: Kovacs
authors.affiliation: Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, 3, 37077, Göttingen, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Kramm
authors.affiliation: Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Asteroiden und Kometen, Rutherfordstraﬂe 2, 12489 Berlin, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Kührt
authors.affiliation: Operations Department, European Space Astronomy Centre/ESA, P.O. Box 78, 28691 Villanueva de la Canada, Madrid, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Küppers
authors.affiliation: Instituto de Astrofisica de Andalucia (CSIC), c/ Glorieta de la Astronomia s/n, 18008 Granada, Spain.
authors.forename: M L
authors.initials: ML
authors.lastname: Lara
authors.affiliation: Department of Physics and Astronomy, University of Padova, Vicolo dell'Osservatorio 3, 35122 Padova, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Lazzarin
authors.affiliation: Instituto de Astrofisica de Andalucia (CSIC), c/ Glorieta de la Astronomia s/n, 18008 Granada, Spain.
authors.forename: J J Lopez
authors.initials: JJ
authors.lastname: Moreno
authors.affiliation: Department of Physics and Astronomy, University of Padova, Vicolo dell'Osservatorio 3, 35122 Padova, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Marzari
authors.affiliation: Dipartimento di Geoscienze, University of Padova, Via G. Gradenigo 6, 35131 Padova, Italy.|Center of Studies and Activities for Space (CISAS), G. Colombo, University of Padova, Via Venezia 15, 35131 Padova, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Massironi
authors.affiliation: University of Padova, Department of Information Engineering, Via Gradenigo 6/B, 35131 Padova, Italy.|Center of Studies and Activities for Space (CISAS), G. Colombo, University of Padova, Via Venezia 15, 35131 Padova, Italy.|CNR-IFN UOS Padova LUXOR, Via Trasea, 7, 35131 Padova, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Naletto
authors.affiliation: Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, 3, 37077, Göttingen, Germany.
authors.forename: N
authors.initials: N
authors.lastname: Oklay
authors.affiliation: NASA Ames Research Center, Moffett Field, CA 94035, USA.|Center of Studies and Activities for Space (CISAS), G. Colombo, University of Padova, Via Venezia 15, 35131 Padova, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Pajola
authors.affiliation: Physikalisches Institut der Universität Bern, Sidlerstrasse 5, 3012 Bern, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Pommerol
authors.affiliation: Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Asteroiden und Kometen, Rutherfordstraﬂe 2, 12489 Berlin, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Preusker
authors.affiliation: Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Asteroiden und Kometen, Rutherfordstraﬂe 2, 12489 Berlin, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Scholten
authors.affiliation: Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, 3, 37077, Göttingen, Germany.
authors.forename: X
authors.initials: X
authors.lastname: Shi
authors.affiliation: Physikalisches Institut der Universität Bern, Sidlerstrasse 5, 3012 Bern, Switzerland.
authors.forename: N
authors.initials: N
authors.lastname: Thomas
authors.affiliation: MTA CSFK Konkoly Observatory, Konkoly Thege M. ut 15-17, H1121 Budapest, Hungary.
authors.forename: I
authors.initials: I
authors.lastname: Toth
authors.affiliation: Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, 3, 37077, Göttingen, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Tubiana
authors.affiliation: Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, 3, 37077, Göttingen, Germany.
authors.forename: J-B
authors.initials: JB
authors.lastname: Vincent