Letter

The pristine interior of comet 67P revealed by the combined Aswan outburst and cliff collapse

  • Nature Astronomy 1, Article number: 0092 (2017)
  • doi:10.1038/s41550-017-0092
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Abstract

Outbursts occur commonly on comets1 with different frequencies and scales2,3. Despite multiple observations suggesting various triggering processes4,5, the driving mechanism of such outbursts is still poorly understood. Landslides have been invoked6 to explain some outbursts on comet 103P/Hartley 2, although the process required a pre-existing dust layer on the verge of failure. The Rosetta mission observed several outbursts from its target comet 67P/Churyumov–Gerasimenko, which were attributed to dust generated by the crumbling of materials from collapsing cliffs7,8. However, none of the aforementioned works included definitive evidence that landslides occur on comets. Amongst the many features observed by Rosetta on the nucleus of the comet, one peculiar fracture, 70 m long and 1 m wide, was identified on images obtained in September 2014 at the edge of a cliff named Aswan9. On 10 July 2015, the Rosetta Navigation Camera captured a large plume of dust that could be traced back to an area encompassing the Aswan escarpment7. Five days later, the OSIRIS camera observed a fresh, sharp and bright edge on the Aswan cliff. Here we report the first unambiguous link between an outburst and a cliff collapse on a comet. We establish a new dust-plume formation mechanism that does not necessarily require the breakup of pressurized crust or the presence of supervolatile material, as suggested by previous studies7. Moreover, the collapse revealed the fresh icy interior of the comet, which is characterized by an albedo >0.4, and provided the opportunity to study how the crumbling wall settled down to form a new talus.

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Acknowledgements

We thank M. Delbo for comments that led to substantial improvement of the paper. OSIRIS was built by a consortium of the Max-Planck-Institut für Sonnensystemforschung, in Göttingen, Germany, CISAS-University of Padova, Italy, the Laboratoire d’Astrophysique de Marseille, France, the Instituto de Astrofísica de Andalucia, CSIC, Granada, Spain, the Research and Scientific Support Department of the European Space Agency, Noordwijk, The Netherlands, the Instituto Nacional de Tecnica Aeroespacial, Madrid, Spain, the Universidad Politechnica de Madrid, Spain, the Department of Physics and Astronomy of Uppsala University, Sweden, and the Institut für Datentechnik und Kommunikationsnetze der Technischen Universität Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), Italy (ASI), France (CNES), Spain (MEC), Sweden (SNSB) and the ESA Technical Directorate is gratefully acknowledged. We thank the ESA teams at ESAC, ESOC and ESTEC for their work in support of the Rosetta mission. M.P. was supported for this research by an appointment to the NASA Postdoctoral Program at the Ames Research Center administered by Universities Space Research Association (USRA) through a contract with NASA. M.F.A. acknowledges NASA funding through Jet Propulsion Laboratory contract no. 1267923 and from the Akademie der Wissenschaften zu Göttingen. W.-H.I acknowledges the Ministry of Science and Technology, Taiwan (grant no. NSC 102-2112-M-008) and Macau University of Science and Technology (grant no. FDCT 017/2014/A1).

Author information

Affiliations

  1. NASA Ames Research Center, Moffett Field, California 94035, USA.

    • M. Pajola
  2. Center of Studies and Activities for Space, CISAS, ‘G. Colombo’, University of Padova, via Venezia 15, 35131 Padova, Italy.

    • M. Pajola
    • , G. Naletto
    • , C. Barbieri
    • , I. Bertini
    • , S. Ferrari
    •  & F. Ferri
  3. Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany.

    • S. Höfner
    • , J. B. Vincent
    • , N. Oklay
    • , C. Güttler
    • , C. Tubiana
    • , H. Sierks
    • , J. Agarwal
    • , S. Boudreault
    • , J. Deller
    • , M. Hofmann
    • , G. Kovacs
    •  & J. R. Kramm
  4. Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Rutherfordstrasse 2, 12489 Berlin, Germany.

    • J. B. Vincent
    • , N. Oklay
    • , F. Scholten
    • , F. Preusker
    • , S. Mottola
    • , H. U. Keller
    • , S. F. Hviid
    • , J. Knollenberg
    •  & E. Kührt
  5. Department of Information Engineering, University of Padova, via Gradenigo 6/B, 35131 Padova, Italy.

    • G. Naletto
  6. CNR-IFN UOS Padova LUXOR, via Trasea 7, 35131 Padova, Italy.

    • G. Naletto
    • , V. Da Deppo
    •  & E. Simioni
  7. LESIA, Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, Sorbonne Paris Cité, UPMC, Paris 06, Sorbonne Universités, 5 Place J. Janssen, Meudon Principal Cedex 92195, France.

    • S. Fornasier
    • , C. Feller
    • , P. H. Hasselmann
    • , M. A. Barucci
    •  & J. D. P. Deshapriya
  8. The University of Kent, School of Physical Sciences, Canterbury, Kent CT2 7NZ, UK.

    • S. Lowry
  9. Department of Physics and Astronomy ‘G. Galilei’, University of Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy.

    • C. Barbieri
    • , M. Lazzarin
    •  & F. Marzari
  10. Aix-Marseille Université, CNRS LAM (Laboratoire d’Astrophysique de Marseille), UMR 7326, 13388 Marseille, France.

    • P. Lamy
    • , O. Groussin
    • , L. Jorda
    •  & I. Toth
  11. Centro de Astrobiologia, CSIC-INTA, 28850 Torrejon de Ardoz, Madrid, Spain.

    • R. Rodrigo
  12. International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland.

    • R. Rodrigo
  13. Scientific Support Office, European Space Research and Technology Centre/ESA, Keplerlaan 1, Postbus 299, 2201 AZ Noordwijk ZH, The Netherlands.

    • D. Koschny
  14. Department of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden.

    • H. Rickman
  15. PAS Space Research Center, Bartycka 18A, 00716 Warszawa, Poland.

    • H. Rickman
  16. Institut für Geophysik und extraterrestrische Physik (IGEP), Technische Universität Braunschweig, Mendelssohnstrasse 3, 38106 Braunschweig, Germany.

    • H. U. Keller
  17. Department for Astronomy, University of Maryland, College Park, Maryland 20742-2421, USA.

    • M. F. A’Hearn
  18. LATMOS, CNRS/UVSQ/IPSL, 11 boulevard d’Alembert, 78280 Guyancourt, France.

    • J.-L. Bertaux
  19. Operations Department European Space Astronomy Centre/ESA, PO Box 78, 28691 Villanueva de la Canada, Madrid, Spain.

    • S. Besse
    •  & M. Küppers
  20. INAF Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy.

    • G. Cremonese
    • , A. Lucchetti
    •  & E. Simioni
  21. NASA Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, California 91109, USA.

    • B. Davidsson
  22. Department of Mechanical Engineering, University of Padova, via Venezia 1, 35131 Padova, Italy.

    • S. Debei
  23. UNITN, University of Trento, via Mesiano, 77, 38100 Trento, Italy.

    • M. De Cecco
  24. Physikalisches Institut der Universität Bern, Sidlerstrasse 5, 3012 Bern, Switzerland.

    • M. R. El-Maarry
    • , A. Pommerol
    •  & N. Thomas
  25. Laboratory for Atmospheric and Space Physics, University of Colorado, 3665 Discovery Drive, Boulder, Colorado 80301, USA.

    • M. R. El-Maarry
  26. INAF Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy.

    • M. Fulle
  27. Instituto de Astrofisica de Andalucia CSIC, Glorieta de la Astronomia, 18008 Granada, Spain.

    • P. Gutierrez
    • , L. M. Lara
    •  & J. J. Lopez Moreno
  28. Institute for Space Science, National Central University, 32054 Chung-Li, Taiwan.

    • W.-H. Ip
    •  & Z.-Y. Lin
  29. Space Science Institute, Macau University of Science and Technology, Macau, China.

    • W.-H. Ip
  30. Budapest University of Technology and Economics, Budapest, Hungary.

    • G. Kovacs
  31. Geosciences Department, University of Padova, via G. Gradenigo 6, 35131 Padova, Italy.

    • M. Massironi
    •  & L. Penasa
  32. Institut für Datentechnik und Kommunikationsnetze der TU Braunschweig, Hans-Sommer-Strasse 66, 38106 Braunschweig, Germany.

    • H. Michalik
  33. Observatory of the Hungarian Academy of Sciences, PO Box 67, 1525 Budapest, Hungary.

    • I. Toth
  34. School of Civil Engineering, Department DICAM, University of Bologna, Bologna, Italy.

    • E. Baratti

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Contributions

M.P. conceived, led and designed the study, analysed the cliff setting before and after the collapse, contributed to the spectrophotometric study, made the overall boulder size–frequency analysis and wrote the main text and Methods; S.H. carried out the thermophysical analysis and wrote part of the main text and Methods; J.B.V. performed the outburst analysis and wrote part of the main text; N.O. carried out the 6 August 2016 post-collapse spectrophotometric analysis, wrote part of the main text and Methods; F.S. and F.P. were responsible for the stereo-photoclinometric model and the 3D reconstruction of the pre- and post-collapse cases, and wrote part of the main text and Methods; S.M. contributed to the thermophysical analysis and made the illumination conditions video of 10 July 2015; G.N. contributed to designing the study and data interpretation; S.F carried out the 19 July 2015 spectrophotometric analysis, wrote part of the main text and Methods; S.L. contributed to the thermophysical analysis and wrote part of the main text; C.F. and P.H.H. contributed to the spectrophotometric study; C.G. and C.T. contributed to the data interpretation and made the Aswan observations possible; H.S., C.B., P.L., R.R., D.K. and H.R. are the lead scientists of the OSIRIS project. The other authors are all co-investigators who built and ran this instrument and made the observations possible, and associates and assistants who participated in the study.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to M. Pajola.

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    Supplementary Figures 1–7, Supplementary Tables 1–2 and Supplementary Video 1 caption.

Videos

  1. 1.

    Supplementary Video 1

    Video representation of the illumination conditions at the Aswan cliff and plateau on 10 July 2015.