Letter

Fission and reconfiguration of bilobate comets as revealed by 67P/Churyumov–Gerasimenko

Received:
Accepted:
Published online:

Abstract

The solid, central part of a comet—its nucleus—is subject to destructive processes1,2, which cause nuclei to split at a rate of about 0.01 per year per comet3. These destructive events are due to a range of possible thermophysical effects4; however, the geophysical expressions of these effects are unknown. Separately, over two-thirds of comet nuclei that have been imaged at high resolution show bilobate shapes5, including the nucleus of comet 67P/Churyumov–Gerasimenko (67P), visited by the Rosetta spacecraft. Analysis of the Rosetta observations suggests that 67P’s components were brought together at low speed after their separate formation6. Here, we study the structure and dynamics of 67P’s nucleus. We find that sublimation torques have caused the nucleus to spin up in the past to form the large cracks observed on its neck. However, the chaotic evolution of its spin state has so far forestalled its splitting, although it should eventually reach a rapid enough spin rate to do so. Once this occurs, the separated components will be unable to escape each other; they will orbit each other for a time, ultimately undergoing a low-speed merger that will result in a new bilobate configuration. The components of four other imaged bilobate nuclei have volume ratios that are consistent with a similar reconfiguration cycle, pointing to such cycles as a fundamental process in the evolution of short-period comet nuclei. It has been shown7,8 that comets were not strong contributors to the so-called late heavy bombardment about 4 billion years ago. The reconfiguration process suggested here would preferentially decimate comet nuclei during migration to the inner solar system, perhaps explaining this lack of a substantial cometary flux.

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Acknowledgements

M.H. acknowledges the use of ANSYS Academic APDL, version 15.03. D.J.S. and M.H. were supported by NASA grants NNX14AL16G, NNX14AB08G and NNA14AB03A. S.R.C. carried out his work at the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. S.M. acknowledges support by the Jet Propulsion Laboratory.

Author information

Author notes

    • Masatoshi Hirabayashi

    Present address: Department of Earth, Atmospheric and Planetary Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, Indiana 47907, USA.

Affiliations

  1. Department of Aerospace Engineering Sciences, University of Colorado Boulder, 429 UCB, Boulder, Colorado 80309, USA

    • Masatoshi Hirabayashi
    • , Daniel J. Scheeres
    •  & Jay W. McMahon
  2. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, USA

    • Steven R. Chesley
    •  & Shantanu P. Naidu
  3. Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder, Colorado 80302, USA

    • Simone Marchi
  4. Department of Earth, Atmospheric and Planetary Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, Indiana 47907, USA

    • Jordan Steckloff
  5. German Aerospace Center (DLR), Institute of Planetary Research, Rutherfordstr. 2, 12489 Berlin, Germany

    • Stefano Mottola
  6. Department of the Geophysical Sciences, University of Chicago, 5734 S. Ellis Avenue, Chicago, Illinois 60637, USA

    • Timothy Bowling

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Contributions

M.H. conducted structure analysis. D.J.S., S.R.C., J.W.M. and M.H. analysed orbital and spin evolution. S.P.N. produced reduced data sets for the analysis. M.H., D.J.S., S. Ma., J.S., S. Mo. and T.B. discussed the meaning of the discovered relationships. M.H. wrote the paper with guidance from D.J.S. T.B. generated high-resolution figures. All authors commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Masatoshi Hirabayashi or Daniel J. Scheeres.

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