The Strength of Cometary Surface Material: Relevance of Deep Impact Results for Philae Landing on a Comet

  • J. Biele
  • S. Ulamec
  • L. Richter
  • E. Kührt
  • J. Knollenberg
  • D. Möhlmann
  • the Philae Team
Part of the Eso Astrophysics Symposia book series (ESO)


We discuss the Deep Impact estimates of strength of the surface material of comet Tempel 1. It appears doubtful that the tensile strength is as low as originally published. The method applied neglects the weakening by the shock wave, the acceleration by gas and the ongoing discussion whether gravity or strength craters are consistent with the observations. The various definitions of strength (tensile, shear, compressive, dynamic strength) and its size-dependency are discussed. Even for extremely low cohesion, a lower limit of ≈ 1 kPa for the quasi-static compressive strength at dm-scales is derived; far more likely is a compressive strength of the order of ≈ 10 kPa for very soft comet surfaces. The Rosetta lander, Philae, will touchdown on comet Churyumov-Gerasimenko in November 2014. A soft comet surface with a compressive strength ⩾ 4 kPa indeed facilitates landing and leads to a penetration of the order of only 20 cm according to our model calculations.


Compressive Strength Landing Gear Cometary Nucleus Deep Impact Cometary Material 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. 1.
    A’Hearn, M.F. et al. (2005), Deep Impact: Excavating Comet Tempel 1, Science 310, 258CrossRefADSGoogle Scholar
  2. 2.
    Peplow, M., Comet reveals crumbly guts. Deep Impact results suggest Rosetta lander is in for a rough time,, published online, 8 September 2005, doi: 10.1038/news050905-15,
  3. 3.
    Ai, H.-A., and Ahrens, T.J. (2004), Dynamic Tensile Strength of Terrestrial Rocks and Application to Impact Cratering, Meteorit. Planet. Sci., 39, 233–246.ADSCrossRefGoogle Scholar
  4. 4.
    Stewart, S. T., and T. J. Ahrens (1999), Correction to the dynamic tensile 1606 strength of ice and ice-silicate mixtures (Lange and Ahrens 1983), Proc. 1607 Lunar Planet. Sci. Conf., 30th, abstract 2037Google Scholar
  5. 5.
    Xu, Y. (2005), Explanation of scaling phenomena based on fractal fragmentation, Mech. Res. Comm. 32, 209zbMATHCrossRefGoogle Scholar
  6. 6.
    Petrovic, J.J. (2003), Mechanical properties of ice and snow, Review, J. Mat. Sci. 38 1CrossRefADSMathSciNetGoogle Scholar
  7. 7.
    Asphaug, E. and Benz, W. (1996), Size, Density, and Structure of Comet Shoemaker-Levy 9 inferred from the Physics of Tidal Breakup, Icarus 121, 225CrossRefADSGoogle Scholar
  8. 8.
    Keller, H.-U., et al. (2006), Observations of Comet 9P/Tempel 1 around the Deep Impact event by the OSIRIS cameras onboard Rosetta, Icarus (accepted)Google Scholar
  9. 9.
    Lichtenegger, H. I. M.; Komle, N. I. (1991), Heating and evaporation of icy particles in the vicinity of comets, Icarus 90, 319–325CrossRefADSGoogle Scholar
  10. 10.
    E.H. Beer, M. Podolak ., D. Prialnik (2006), The contribution of icy grains to the activity of comets I. Grain lifetime and distribution, Icarus 180, 473CrossRefADSGoogle Scholar
  11. Jorda, L., Lamy, P., Faury, G. , Keller, H. U. , Hviid, S., Küppers, M., Koschny, D., Lecacheux, J., Gutierrez, P., Lara, L. M. (2006), Properties of the DEEP IMPACT Dust Cloud Icarus (accepted)Google Scholar
  12. Holsapple, K.A., Housen, K.R. (2006), Gravity or Strength? An Interpretation of the Deep Impact Experiment. 37th Annual Lunar and Planetary Science Conference XXXVII, March 13–17, 2006, League City, Texas, abstract no.1068Google Scholar
  13. 13.
    Housen, K.R., Schmidt, R.M., Holsapple, K.A. (1983), Craterejecta scaling laws - Fundamental forms based on dimensional analysis. J. Geophys. Res. 88, 2485CrossRefADSGoogle Scholar
  14. 14.
    Housen, K.R. and Holsapple, K.A. (2003), Impact cratering on porous asteroids, Icarus 163, 102CrossRefADSGoogle Scholar
  15. 15.
    Belton, Michael J.S. et al., The Internal Structure of Jupiter Family Cometary Nuclei from Deep Impact Observations: The Talps or Layered Pile Model, Icarus: submitted June 1 2006; Revised: July 27, 2006Google Scholar
  16. 16.
    Kührt, E., Keller, H. U. (1994), The formation of cometary surface crusts, Icarus, 109, 121–132CrossRefADSGoogle Scholar
  17. 17.
    Jessberger, H. L.; Kotthaus, M. , Compressive strength of synthetic comet nucleus samples, in Hunt J., Guyeme T. D., eds, ESA SP-302, Proceedings of the International Workshop on Physics and Mechanics of Cometary Materials, ESA Publications Division, Noordwijk, p. 141Google Scholar
  18. 18.
    GH Heiken, DT Vaniman, MF Bevan (eds.) The Lunar Source Book, (Cambridge University Press 1991)Google Scholar
  19. 19.
    Kemurdzhian, A. L.; Gromov, V. V.; Shvarev, V. V. In: Soviet progress in space studies: The second decade of space flight, 1967–1977. (Moscow, Izdatel’stvo Nauka, 1978) p. 352–380. In Russian.Google Scholar
  20. 20.
    Richter, L.O., Inferences of Strength of Soil Deposits Along MER Rover Traverses, American Geophysical Union, Fall Meeting 2005, abstract #P21A-0134Google Scholar
  21. 21.
    Toth, I., Lisse, C.M. (2006), On the rotational breakup of cometary nuclei and centaurs, Icarus 181, 162CrossRefADSGoogle Scholar
  22. 22.
    Greenberg, J.M., Mizutani, H., Yamamoto, T., 1995. A new derivation of the tensile strength of cometary nuclei: Application to Comet Shoemaker-Levy 9. Astron. Astrophys. 295, L35–L38 (1995)ADSGoogle Scholar
  23. 23.
    Sirono, S.-i. and J. M. Greenberg (2000), Do Cometesimal Collisions Lead to Bound Rubble Piles or to Aggregates Held Together by Gravity? Icarus 145, 230–238CrossRefADSGoogle Scholar
  24. 24.
    Klinger J., Espinasse S., Schmidt B., 1989, in Hunt J., Guyeme T. D., eds, ESA SP-302, Proceedings of the International Workshop on Physics and Mechanics of Cometary Materials. ESA Publications Division, Noordwijk, p. 197Google Scholar
  25. 25.
    Brownlee, D.E. et al., Surface of young Jupiter family comet 81P/Wild 2: View from the Stardust spacecraft, Science 304, 1764 (2004)Google Scholar
  26. 26.
    Blum, J., R. Schräpler, et al. (2006), The Physics of Protoplanetesimal Dust Agglomerates I. Mechanical Properties and Relations to Primitive Bodies in the Solar System, Astrophysical Journal, 652, 1768–1781CrossRefADSGoogle Scholar
  27. 27.
    Wetherill, G. W.; Revelle, D. O., Relationships between comets, large meteors, and meteorites, In: Comets (University of Arizona , Tucson, AZ, 1982) pp. 297–319.Google Scholar
  28. 28.
    Trigo-Rodríguez and Llorca, Jordi, The strength of cometary meteoroids: clues to the structure and evolution of comets. Mon. Not. R. Astron. Soc (2006, in press) and erratum (2006, in press)Google Scholar
  29. 29.
    Mellor, M. (1975): A Review of Basic Snow Mechanics, Snow Mechanics Symposium; Proceeding of the Grindelwald Symposium, Grindelwald, Bernese Oberland (Switzerland) April 1974: International Association of Hydrological Sciences Publication No. 114, 251–291,Google Scholar
  30. 30.
    Bar-Nun, A., Pat-El, I., Laufer, D. (2006), Comparison between the findings of Deep Impact and our experimental results on large samples of gas-laden amorphous ice, Icarus, 191, 562–566CrossRefGoogle Scholar
  31. 31.
    Davidsson, B. J. R. (2001), Tidal Splitting and Rotational Breakup of Solid Biaxial Ellipsoids. Icarus 149, 375–383CrossRefADSGoogle Scholar
  32. 32.
    Chokshi, A., A. Tielens,G. G. M. et al. (1993), Dust coagulation, Astrophysical Journal Part 1 407(2), 806–819CrossRefADSGoogle Scholar
  33. 33.
    Terzaghi, K.: Theoretische Bodenmechanik, (Springer, Berlin/Göttingen New York, 1954)Google Scholar
  34. 34.
    Craig, R.F.: Craig’s Soil mechanics, 7th ed., (Spon Press, London, New York 2003)Google Scholar
  35. 35.
    Holsapple, K.A. and Michel, P. (2006), Tidal disruptions: Acontinuum theory for solid bodies, Icarus 183, 331–348CrossRefADSGoogle Scholar
  36. 36.
    Wong, J.Y., Terramechanics and off-road vehicles, (Elsevier, Amsterdam 1989)Google Scholar
  37. 37.
    Kömle, N.I., Kargl, G., Ball, A.J., Lorenz, R.D. (eds.), Penetrometry in the Solar System. Proceedings of the International Workshop of Penetrometry in the Solar System, Graz, Austria, 1999. Verlag der österreichischen Akademie der Wissenschaften, (Wien 2001)Google Scholar
  38. 38.
    Johnson, J. B., A physically based penetration equation for compressible materials. In: cite Koemle2001 K¨mle, N.I., Kargl, G., Ball, A.J., Lorenz, R.D. (eds.), Penetrometry in the Solar System. Proceedings of the International Workshop of Penetrometry in the Solar System, Graz, Austria, 1999. (Verlag der österreichischen Akademie der Wissenschaften, Wien 2001), pp. 73–85Google Scholar
  39. 39.
    Biele, J. (2002), The Experiments onboard the ROSETTA Lander, Earth, Moon, and Planets, 90, 445–458Google Scholar
  40. 40.
    Ulamec, S. et al. (2006), Rosetta Lander – Philae: Implications of an alternative mission, Acta Astronautica 58, 435–441CrossRefADSGoogle Scholar
  41. 41.
    Davidsson, B.J.R., Gutiérrez, P.J. (2005), Nucleus properties of Comet 67P/ Churyumov Gerasimenko estimated from non-gravitational force modeling, Icarus 176, 453–477CrossRefADSGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2009

Authors and Affiliations

  • J. Biele
    • 1
  • S. Ulamec
    • 2
  • L. Richter
    • 1
  • E. Kührt
    • 2
  • J. Knollenberg
    • 2
  • D. Möhlmann
    • 2
  • the Philae Team
    1. 1.DLRInstitute for Space Simulation CologneGermany
    2. 2.DLRInstitute for Planetary ResearchBerlinGermany

    Personalised recommendations