title: The diurnal cycle of water ice on comet 67P/Churyumov-Gerasimenko.
abstract: Observations of cometary nuclei have revealed a very limited amount of surface water ice, which is insufficient to explain the observed water outgassing. This was clearly demonstrated on comet 9P/Tempel 1, where the dust jets (driven by volatiles) were only partially correlated with the exposed ice regions. The observations of 67P/Churyumov-Gerasimenko have revealed that activity has a diurnal variation in intensity arising from changing insolation conditions. It was previously concluded that water vapour was generated in ice-rich subsurface layers with a transport mechanism linked to solar illumination, but that has not hitherto been observed. Periodic condensations of water vapour very close to, or on, the surface were suggested to explain short-lived outbursts seen near sunrise on comet 9P/Tempel 1. Here we report observations of water ice on the surface of comet 67P/Churyumov-Gerasimenko, appearing and disappearing in a cyclic pattern that follows local illumination conditions, providing a source of localized activity. This water cycle appears to be an important process in the evolution of the comet, leading to cyclical modification of the relative abundance of water ice on its surface.
authors.affiliation: Istituto di Astrofisica e Planetologia Spaziali - INAF, via del fosso del cavaliere 100, 00133 Rome, Italy.
authors.forename: M C
authors.initials: MC
authors.lastname: De Sanctis
authors.affiliation: Istituto di Astrofisica e Planetologia Spaziali - INAF, via del fosso del cavaliere 100, 00133 Rome, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Capaccioni
authors.affiliation: Istituto di Astrofisica e Planetologia Spaziali - INAF, via del fosso del cavaliere 100, 00133 Rome, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Ciarniello
authors.affiliation: Istituto di Astrofisica e Planetologia Spaziali - INAF, via del fosso del cavaliere 100, 00133 Rome, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Filacchione
authors.affiliation: Istituto di Astrofisica e Planetologia Spaziali - INAF, via del fosso del cavaliere 100, 00133 Rome, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Formisano
authors.affiliation: Institute for Planetary Research, DLR, Rutherfordstraße 2, 12489 Berlin, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Mottola
authors.affiliation: Istituto di Astrofisica e Planetologia Spaziali - INAF, via del fosso del cavaliere 100, 00133 Rome, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Raponi
authors.affiliation: Istituto di Astrofisica e Planetologia Spaziali - INAF, via del fosso del cavaliere 100, 00133 Rome, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Tosi
authors.affiliation: LESIA-Observatoire de Paris, CNRS, Université Pierre et Marie Curie, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France.
authors.forename: D
authors.initials: D
authors.lastname: Bockelée-Morvan
authors.affiliation: LESIA-Observatoire de Paris, CNRS, Université Pierre et Marie Curie, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France.
authors.forename: S
authors.initials: S
authors.lastname: Erard
authors.affiliation: LESIA-Observatoire de Paris, CNRS, Université Pierre et Marie Curie, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France.
authors.forename: C
authors.initials: C
authors.lastname: Leyrat
authors.affiliation: Université Grenoble Alpes - CNRS Institut de Planetologie et Astrophysique de Grenoble, Batiment D de Physique, BP 53, 38041 Grenoble Cedex 9, France.
authors.forename: B
authors.initials: B
authors.lastname: Schmitt
authors.affiliation: Istituto di Astrofisica e Planetologia Spaziali - INAF, via del fosso del cavaliere 100, 00133 Rome, Italy.|University of California, Los Angeles, California 90095, USA.
authors.forename: E
authors.initials: E
authors.lastname: Ammannito
authors.affiliation: Institute for Planetary Research, DLR, Rutherfordstraße 2, 12489 Berlin, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Arnold
authors.affiliation: LESIA-Observatoire de Paris, CNRS, Université Pierre et Marie Curie, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France.
authors.forename: M A
authors.initials: MA
authors.lastname: Barucci
authors.affiliation: Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, 2455 Hayward Street, Ann Arbor, Michigan 48109, USA.
authors.forename: M
authors.initials: M
authors.lastname: Combi
authors.affiliation: Istituto di Astrofisica e Planetologia Spaziali - INAF, via del fosso del cavaliere 100, 00133 Rome, Italy.
authors.forename: M T
authors.initials: MT
authors.lastname: Capria
authors.affiliation: Istituto di Astrofisica e Planetologia Spaziali - INAF, via del fosso del cavaliere 100, 00133 Rome, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Cerroni
authors.affiliation: National Central University, No. 300, Jhongda Road, Jhongli District, Taoyuan City, 32001 Taipei, Taiwan.
authors.forename: W-H
authors.initials: WH
authors.lastname: Ip
authors.affiliation: Institute for Planetary Research, DLR, Rutherfordstraße 2, 12489 Berlin, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Kuehrt
authors.affiliation: Bear Fight Institute, 22 Fiddler's Road, Box 667, Winthrop, Washington 98862, USA.
authors.forename: T B
authors.initials: TB
authors.lastname: McCord
authors.affiliation: Istituto di Astrofisica e Planetologia Spaziali - INAF, via del fosso del cavaliere 100, 00133 Rome, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Palomba
authors.affiliation: Université Grenoble Alpes - CNRS Institut de Planetologie et Astrophysique de Grenoble, Batiment D de Physique, BP 53, 38041 Grenoble Cedex 9, France.
authors.forename: P
authors.initials: P
authors.lastname: Beck
authors.affiliation: Université Grenoble Alpes - CNRS Institut de Planetologie et Astrophysique de Grenoble, Batiment D de Physique, BP 53, 38041 Grenoble Cedex 9, France.
authors.forename: E
authors.initials: E
authors.lastname: Quirico
mesh_terms: D005118:Extraterrestrial Environment / Q000737:chemistry*; D007053:Ice / Q000032:analysis*; D019110:Meteoroids; D013696:Temperature; D013997:Time Factors; D014835:Volatilization
chemical_list: D007053:Ice