Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

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


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.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Locations of the straight cracks and stress peaks on the surface of the Hapi region of 67P.
Figure 2: Terminal failure states for the 67P nucleus.
Figure 3: Failure types and conditions at different spin periods.
Figure 4: Dynamical variation of factors controlling spin acceleration.


  1. Rickman, H. et al. Comet 67P/Churyumov-Gerasimenko: constraints on its origin from OSIRIS observations. Astron. Astrophys. 583, A44 (2015)

    Article  Google Scholar 

  2. Guilbert-Lepoutre, A. et al. On the evolution of comets. Space Sci. Rev. 197, 271–296 (2015)

    Article  ADS  Google Scholar 

  3. Chen, J. & Jewitt, D. On the rate at which comets split. Icarus 108, 265–271 (1994)

    Article  ADS  Google Scholar 

  4. Boehnhardt, H. in Comets II (eds Festou, M., Keller, H. U. & Weaver, H. A. ) 301–316 (Univ. Arizona Press, 2004)

  5. Keller, H. U. et al. Isolation, erosion, and morphology of comet 67P/Churyumov-Gerasimenko. Astron. Astrophys. 583, A34 (2015)

    CAS  Article  Google Scholar 

  6. Massironi, M. et al. Two independent and primitive envelopes of the bilobate nucleus of comet 67P. Nature 526, 402–405 (2015)

    CAS  Article  ADS  Google Scholar 

  7. Kring, D. A. & Cohen, B. A. Cataclysmic bombardment throughout the inner solar system 3.9–4.0 Ga. J. Geophys. Res. 107, 4 (2002)

    Google Scholar 

  8. Strom, R. G., Malhotra, R., Ito, T., Yoshida, F. & Kring, D. A. The origin of planetary impactors in the inner solar system. Science 309, 1847–1850 (2005)

    CAS  Article  ADS  Google Scholar 

  9. Sierks, H. et al. On the nucleus structure and activity of comet 67P/Churyumov-Gerasimenko. Science 347, (2015)

  10. El-Maarry, M. R. et al. Fractures on comet 67P/Churyumov-Gerasimenko observed by Rosetta/OSIRIS. Geophys. Res. Lett. 42, 5170–5178 (2015)

    Article  ADS  Google Scholar 

  11. Mottola, S. et al. The rotation state of 67P/Churyumov-Gerasimenko from approach observations with the OSIRIS cameras on Rosetta. Astron. Astrophys. 569, L2 (2014)

    Article  ADS  Google Scholar 

  12. Barnes, T. & Farnham, T. Shape models of 67P/Churyumov-Gerasimenko v1.0, RO-C-multi-5-67P-shape-v1.0. NASA Planetary Data System and ESA Planetary Science Archive 2015

  13. Preusker, F. et al. Shape model, reference system definition, and cartographic mapping standards for comet 67P/Churyumov-Gerasimenko—stereo-photogrammetric analysis of Rosetta/OSIRIS image data. Astron. Astrophys. 583, A33 (2015)

    Article  Google Scholar 

  14. Pollard, D. D. & Fletcher, R. C. Fundamentals of Structural Geology 1st edn (Cambridge Univ. Press, 2005)

  15. Biele, J. et al. The landing(s) of Philae and inferences about comet surface mechanical properties. Science 349, aaa9816–aaa9816-6 (2015)

    Article  Google Scholar 

  16. Groussin, O. et al. Gravitational slopes, geomorphology, and material strengths of the nucleus of comet 67P/Churyumov-Gerasimenko from OSIRIS observations. Astron. Astrophys. 583, A32 (2015)

    Article  Google Scholar 

  17. Steckloff, J. K. et al. Dynamic sublimation pressure and the catastrophic breakup of comet ISON. Icarus 258, 430–437 (2015)

    Article  ADS  Google Scholar 

  18. Scheeres, D. J. Rotational fission of contact binary asteroids. Icarus 189, 370–385 (2007)

    Article  ADS  Google Scholar 

  19. Jutzi, M. & Asphaug, E. The shape and structure of cometary nuclei as a result of low-velocity accretion. Science 348, 1355–1358 (2015)

    CAS  Article  ADS  Google Scholar 

  20. Keller, H. U., Mottola, S., Skorov, Y. & Jorda, L. The changing rotation period of comet 67P/Churyumov-Gerasimenko controlled by its activity. Astron. Astrophys. 579, L5 (2015)

    Article  ADS  Google Scholar 

  21. Scheeres, D. J. The dynamical evolution of uniformly rotating asteroids subject to YORP. Icarus 188, 430–450 (2007)

    Article  ADS  Google Scholar 

  22. Levison, H. F. & Duncan, M. J. The long-term dynamical behavior of short-period comets. Icarus 108, 18–36 (1994)

    Article  ADS  Google Scholar 

  23. Thomas, N. et al. Morphological diversity of comet 67P/Churymov-Gerasimenko. Science 347, aaa0440-1–aaa0440-6 (2015)

    Article  Google Scholar 

  24. Pravec, P. et al. Formation of asteroid pairs by rotational fission. Nature 466, 1085–1088 (2010)

    CAS  Article  ADS  Google Scholar 

  25. Jacobson, S. A. & Scheeres, D. J. Dynamics of rotationally fissioned asteroids: source of observed small asteroid systems. Icarus 214, 161–178 (2011)

    Article  ADS  Google Scholar 

  26. Steckloff, J. K. & Jacobson, S. A. The formation of striae with cometary dust tails by a sublimation-driven YORP-like effect. Icarus 264, 160–171 (2016)

    Article  ADS  Google Scholar 

  27. Hirabayashi, M., Sánchez, D. P. & Scheeres, D. J. Internal structure of asteroids having surface shedding due to rotational instability. Astrophys. J. 808, 63 (2015)

    Article  ADS  Google Scholar 

  28. Marchi, S. et al. The onset of the lunar cataclysm as recorded in its ancient crater populations. Earth Planet. Sci. Lett. 325–326, 27–38 (2012)

    Article  ADS  Google Scholar 

  29. Kohnke, P. 2009, Theory Reference for the Mechanical APDL and Mechanical Applications, 12th edn (ANSYS, Inc.)

  30. Marsden, B. G., Sekanina, Z. & Yeomans, D. K. Comets and nongravitational forces. Astron. J. 78, 211–225 (1973)

    Article  ADS  Google Scholar 

  31. Si, H. TetGen, a Delaunay-based quality tetrahedral mesh generator. ACM Trans. Math. Software 41, 11 (2015)

    MathSciNet  Article  Google Scholar 

  32. Hirabayashi, M. & Scheeres, D.J. Stress and failure analysis of rapidly rotating asteroid (29075) 1950 DA. Astrophys. J. Lett. 798, L8 (2015)

    Article  ADS  Google Scholar 

  33. Hirabayashi, M. & Scheeres, D. J. Analysis of asteroid (216) Kleopatra using dynamical and structural constraints. Astrophys. J. 780, 160 (2014)

    Article  ADS  Google Scholar 

  34. Chen, W. F. & Han, D. J. Plasticity for Structural Engineers Ch. 2 (Springer, 1988)

  35. Byerlee, J. Friction of rocks. Pure Appl. Geophys. 116, 615–626 (1978)

    ADS  Google Scholar 

  36. Willam, K. J. & Warnke, E. P. Constitutive model for the triaxial behaviour of concrete. In IABSE Reports of the Working Commissions 19, III-1–III-30 (1974)

    Google Scholar 

  37. El-Maarry, M. R. et al. Regional surface morphology of comet 67P/Churyumov-Gerasimenko from Rosetta/OSIRIS images. Astron. Astrophys. 583, A26 (2015)

    Article  Google Scholar 

  38. Lambe, T. W. & Whitman, R. V. Soil Mechanics Ch. 11, 12 (John Wiley, 1969)

  39. Jaeger, J. C., Cook, N. G. W. & Zimmerman, R. Fundamentals of Rock Mechanics Ch. 6 (John Wiley, 2009)

  40. Hirabayashi, M. Failure modes and conditions of a cohesive, spherical body due to YORP spin-up. Mon. Not. R. Astron. Soc. 454, 2249–2257 (2015)

    Article  ADS  Google Scholar 

  41. Unger, D. J. Analytical Fracture Mechanics 25–28 (Dover, 1995)

  42. Gross, D. & Seelig, T. Fracture Mechanics Ch. 2, 4 (Springer, 2011)

  43. Wiederhorn, S. M. & Bolz, L. H. Stress corrosion and static fatigue of glass. J. Am. Ceram. Soc. 53, 543–548 (1970)

    CAS  Article  Google Scholar 

  44. Goodman, D. J. Critical stress intensity factor (KIc) measurements at high loading rates for polycrystalline ice in Physics and Mechanics of Ice 129–146 (Springer, 1980)

  45. Atkinson, B. K. Subcritical crack growth in geological materials. J. Geophys. Rev. 89, 4077–4114 (1984)

    CAS  Article  ADS  Google Scholar 

  46. Scheeres, D. J. Stability in the full two body problem. Celestial Mech. Dyn. Astron. 83, 155–169 (2002)

    MathSciNet  Article  ADS  Google Scholar 

  47. McMahon, J. W. & Scheeres, D. J. Improving space object catalog maintenance through advances in solar radiation pressure modeling. J. Guid. Control Dyn. 38, 1366–1381 (2015)

    Article  ADS  Google Scholar 

  48. Farnham, T. L. & Thomas, P. C. Plate shape model of comet 103P/Hartley 2 V1.0, DIF-C-HRIV/MRI-5-HARTLEY2-SHAPE-V1.0. NASA Planetary Data System (2013)

  49. Sagdeev, R. Z. et al. Television observations of comet Halley from Vega spacecraft. Nature 321, 262–266 (1986)

    Article  ADS  Google Scholar 

  50. Keller, H. U., Britt, D., Buratti, B. J. & Thomas, N. In situ observations of cometary nuclei in Comet II (eds Festou, M. C., Keller, H. U. & Weaver, H. A. ) 211–222 (Univ. Arizona Press, 2004)

  51. Harmon, J. K., Nolan, M. C., Giorgini, J. D. & Howell, E. S. Radar observations of 8P/Tuttle: a contact-binary comet. Icarus 207, 499–502 (2010)

    Article  ADS  Google Scholar 

Download references


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

Authors and Affiliations



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.

Corresponding authors

Correspondence to Masatoshi Hirabayashi or Daniel J. Scheeres.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Extended data figures and tables

Extended Data Figure 1 Different types of crack observed on the 67P nucleus.

a, Polygonal cracks on the Apis region at the edge of the large lobe; these cracks are presumably generated by thermal contraction10. b, Parallel sets of cracks on the Hathor region23. Images available at (a) and at (b). Image credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.

Extended Data Figure 2 Tensile regions on the neck cross-section at the force balance point.

The bulk density is assumed to be 535 kg m−3. a, The maximum component of the principal stress at the force balance point, which is 7 h. The region enclosed by the yellow line indicates the neck cross-section. The red region indicates tensile regions. b, Body orientation. Green arrow, maximum moment of inertia axis; red arrow, intermediate moment of inertia axis; blue arrow, minimum moment of inertia axis.

Extended Data Figure 3 Failure types and conditions for different bulk density cases.

a, The bulk density is 500 kg m−3. b, The bulk density is 570 kg m−3.

Source data

Extended Data Figure 4 Elastic analysis for heterogeneous density cases.

The spin period was fixed at 9 h. The contour plots show the maximum component of the principal stress, with units of pascals. a, The bulk density of the neck is zero. The other regions have a bulk density of 578 kg m−3. b, The bulk density of the neck is 1,000 kg m−3, leading to a bulk density of 498 kg m−3 in the other regions. c, Schematic plot of the bulk density distribution.

Extended Data Figure 5 Plastic analysis for a neck density of 0 kg m−3.

The cross-sections displayed are the same as in Fig. 2. The averaged density is fixed at 535 kg m−3. The colours describe the stress ratio. a, Type I failure at 12.4 h. The cohesive strength used was 4 Pa. b, Type II failure at 8 h. The cohesive strength was 45 Pa. c, Type III failure at 5 h. The cohesive strength was 300 Pa. d, Body orientation.

Extended Data Figure 6 Plastic analysis for a bulk density of 1,000 kg m−3.

The cross-sections displayed are the same as in Fig. 2. The averaged density is fixed at 535 kg m−3. The colours describe the stress ratio. a, Type I failure at 12.4 h. The cohesive strength used was 5 Pa. b, Type II failure at 8 h. The cohesive strength was 25 Pa. c, Type III failure at 5 h. The cohesive strength was 200 Pa. d, Body orientation.

Extended Data Figure 7 Volume ratios of cometary nuclei imaged from spacecraft encounters or ground-based radar.

a, 67P/Churyumov–Gerasimenko. Image credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA. b, 103P/Hartley 2. Image credit: EPOXI mission MRI-VIS frame 5004057 from NASA’s Planetary Data System. c, 1P/Halley. Image credit: ESA/MPS. d, 19P/Borrelly. Image credit: PIA03500, Courtesy by NASA/JPL-Caltech. e, 8P/Tuttle. Image credit: Arecibo Observatory scans 800300017-19; resolution 1 μs × 0.5 Hz (see ref. 51 for more information).

PowerPoint slides

Source data

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Hirabayashi, M., Scheeres, D., Chesley, S. et al. Fission and reconfiguration of bilobate comets as revealed by 67P/Churyumov–Gerasimenko. Nature 534, 352–355 (2016).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing