Letter

Nature 437, 987-990 (13 October 2005) | doi:10.1038/nature04236; Received 25 July 2005; Accepted 7 September 2005

A large dust/ice ratio in the nucleus of comet 9P/Tempel 1

Michael Küppers1, Ivano Bertini2, Sonia Fornasier2, Pedro J. Gutierrez3, Stubbe F. Hviid1, Laurent Jorda4, Horst Uwe Keller1, Jörg Knollenberg5, Detlef Koschny6, Rainer Kramm1, Luisa-Maria Lara3, Holger Sierks1, Nicolas Thomas7, Cesare Barbieri2, Philippe Lamy4, Hans Rickman8, Rafael Rodrigo3 & The OSIRIS team33

  1. Max-Planck Institut für Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
  2. Dipartimento di Astronomia and CISAS, Università di Padova, Vicolo dell'Osservatorio 5, 35100 Padova, Italy
  3. Instituto de Astrofisica de Andalucía-CSIC, C/Camino Bajo de Huétor, 50, 18008 Granada, Spain
  4. Laboratoire d'Astrophysique de Marseille, Traverse du Siphon, Les Trois Lucs BP 8, 13376 Marseille, France
  5. DLR Institute for Planetary Research, Rutherfordstr. 2, 12489 Berlin, Germany
  6. European Space Agency, ESTEC, SCI-SB, Keplerlaan 1, Postbus 299, 2200 AG Noordwijk, The Netherlands
  7. Physikalisches Institut, Abteilung Weltraumforschung und Planetologie, Universität Bern, Sidlerstr. 5, 3012 Bern, Switzerland
  8. Uppsala Astronomical Observatory, Box 515, 75120 Uppsala, Sweden
  9. University of Maryland, Department of Astronomy, College Park, Maryland 20742-2421, USA
  10. Università di Padova, Departimento di Ingegneria Meccanica, Via Venezia, 1, 35131 Padova, Italy
  11. Armagh Observatory, College Hill, Armagh BT61 9DG, UK
  12. Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
  13. Observatoire de Paris, Section de Meudon, 92195 Meudon, France
  14. Services d'Aéronomie du CNRS, Route des Gatines, BP 3, 91371 Verrières le Buisson, France
  15. Cornell University, 424 Space Sciences Building, Ithaca, New York 14853-6801, USA
  16. Università di Padova, Departimento di Astronomia, Vicolo dell'Osservatorio 2, 35122 Padova, Italy
  17. Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
  18. Università di Padova, Center of Studies and Activities of Space (CISAS) "G.Colombo", Via Venezia 1, 35151 Padova, Italy
  19. Università di Padova, Center of Studies and Activities of Space (CISAS) "G.Colombo", Via Venezia 1, 35151 Padova, Italy
  20. ISAS, International School for Advanced Studies, Strada Costiera, 11, 34014 Trieste, Italy
  21. Institut für Datentechnik und Kommunikationsnetze der TU Braunschweig, Hans-Sommer-Str. 66, 38106 Braunschweig, Germany
  22. National Central University, Institute of Astronomy, 32054 Chung-Li, Taiwan. 15DLR Institute for Planetary Research, Rutherfordstr. 2, 12489 Berlin, Germany
  23. DLR Institute for Planetary Research, Rutherfordstr. 2, 12489 Berlin, Germany
  24. Laboratoire d'Astrophysique de Marseille (CNRS/LAM), Traverse du Siphon, Les Trois Lucs, BP 8, 13376 Marseille Cedex 12, France
  25. Instituto de Astrofísica de Andalucía, PO Box 3004, Camino Bajo de Huétor 24, 18080 Granada, Spain
  26. Università di Padova, Departimento di Fisica, Via Gradenigo 6A, 35151 Padova, Italy
  27. Università di Padova, Departimento di Elettronica et Informatica, Via Venezia 1, 35151 Padova, Italy
  28. Instituto Nacional de Tecnica Aeroespacial, Carretera de Ajalvir, p.k. 4, 28850 Torrejon de Ardoz (Madrid), Spain
  29. Universidad Politecnica de Madrid, Instituto Ignacio D'Riva, Plaza Cardenal Cisneros s/n, 28040 Madrid, Spain
  30. Laboratoire d'Astrophysique de Marseille (CNRS/LAM), Traverse du Siphon, Les Trois Lucs, BP 8, 13376 Marseille Cedex 12, France
  31. Università di Padova, Departimento di Elettronica et Informatica, Via Venezia 1, 35151 Padova, Italy
  32. European Space Research and Technology Centre, Space Science Department, Keplerlaan 1, Postbus 299, 2201 AZ Noordwijk ZH, The Netherlands
  33. Lists of participants and affiliations appear at the end of the paper

Correspondence to: Michael Küppers1 Correspondence and requests for materials should be addressed to M.K. (Email: kueppers@mps.mpg.de).

Comets spend most of their life in a low-temperature environment far from the Sun. They are therefore relatively unprocessed and maintain information about the formation conditions of the planetary system, but the structure and composition of their nuclei are poorly understood. Although in situ 1 and remote2 measurements have derived the global properties of some cometary nuclei, little is known about their interiors. The Deep Impact mission3 shot a projectile into comet 9P/Tempel 1 in order to investigate its interior. Here we report the water vapour content (1.5 times 1032 water molecules or 4.5 times 106 kg) and the cross-section of the dust (330 km2 assuming an albedo of 0.1) created by the impact. The corresponding dust/ice mass ratio is probably larger than one, suggesting that comets are 'icy dirtballs' rather than 'dirty snowballs' as commonly believed4. High dust velocities (between 110 m s-1 and 300 m s-1) imply acceleration in the comet's coma, probably by water molecules sublimated by solar radiation. We did not find evidence of enhanced activity of 9P/Tempel 1 in the days after the impact, suggesting that in general impacts of meteoroids are not the cause of cometary outbursts.

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