Charon's size and an upper limit on its atmosphere from a stellar occultation (original) (raw)

Nature volume 439, pages 52–54 (2006)Cite this article

Abstract

Pluto and its satellite, Charon (discovered in 1978; ref. 1), appear to form a double planet, rather than a hierarchical planet/satellite couple. Charon is about half Pluto's size and about one-eighth its mass. The precise radii of Pluto and Charon have remained uncertain, leading to large uncertainties on their densities2. Although stellar occultations by Charon are in principle a powerful way of measuring its size, they are rare, as the satellite subtends less than 0.3 microradians (0.06 arcsec) on the sky. One occultation (in 1980) yielded a lower limit of 600 km for the satellite's radius3, which was later refined to 601.5 km (ref. 4). Here we report observations from a multi-station stellar occultation by Charon, which we use to derive a radius, R_C = 603.6 ± 1.4 km (1_σ), and a density of ρ = 1.71 ± 0.08 g cm-3. This occultation also provides upper limits of 110 and 15 (3_σ_) nanobar for an atmosphere around Charon, assuming respectively a pure nitrogen or pure methane atmosphere.

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Acknowledgements

We thank the Conseil Scientifique of the Paris Observatory and the Programme National de Planétologie for supporting part of the observations of this event in South America.

Author information

Authors and Affiliations

  1. Observatoire de Paris, LESIA, 92195, Meudon cedex, France
    B. Sicardy, A. Bellucci, E. Gendron, F. Lacombe, S. Lacour, J. Lecacheux, E. Lellouch, S. Renner, S. Pau, F. Roques & T. Widemann
  2. Université Pierre et Marie Curie, 75252 cedex 5, Paris, France
    B. Sicardy
  3. Observatoire de Paris, IMCCE, 75014, Paris, France
    F. Colas, F. Vachier & R. Vieira Martins
  4. European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, 19, Santiago, Chile
    N. Ageorges, O. Hainaut & O. Marco
  5. International Occultation Timing Association, European Section, 30459, Hannover, Germany
    W. Beisker & E. Hummel
  6. Facultad de Ciencias Astronómicas y Geofísicas, Observatorio Astronómico & Instituto de Astrofísica de La Plata, CONICET, Paseo del Bosque 1900, La Plata, Argentina
    C. Feinstein
  7. Instituto de Astrofísica de La Plata, CONICET, Paseo del Bosque 1900
    C. Feinstein
  8. Complejo Astronómico, El Leoncito, CP J5402DSP, San Juan, Argentina
    H. Levato
  9. Gene Shoemaker Observatory, Casilla 21, San Pedro de Atacama, Chile
    A. Maury
  10. Planétarium de Saint-Etienne, 42100, Saint-Etienne, France
    E. Frappa
  11. Association des Utilisateurs de Détecteurs Electroniques (AUDE), France, c/o F. Colas, 45, Av. Reille, 75014, Paris, France
    B. Gaillard & M. Lavayssière
  12. Campo Catino Austral Observatory, Casilla 21, San Pedro de Atacama, Chile
    M. Di Sora, F. Mallia & G. Masi
  13. Università di Tor Vergata di Roma, Via della Ricerca Scientifica n.1, 00133, Rome, Italy
    G. Masi
  14. Observatoire de Genève, CH-1290, Sauverny, Switzerland
    R. Behrend & F. Carrier
  15. Observatoire de Besançon, BP1615, 25010, Besançon cedex, France
    O. Mousis & P. Rousselot
  16. Observatório Nacional, 20921-400, Rio de Janeiro, Brazil
    R. Vieira Martins, A. Alvarez-Candal, D. Lazzaro, C. Veiga & A. H. Andrei
  17. Observatório do Valongo/UFRJ, CEP 20080-090, Rio de Janeiro, Brazil
    A. H. Andrei, M. Assafin & D. N. da Silva Neto
  18. Observatório CEAMIG-REA, CEP 31545-120, MG, Belo Horizonte, Brazil
    C. Jacques & E. Pimentel
  19. Observatório Astronômico Christus, Universidade de Fortaleza, rua João Carvalho, 630, CEP 60140-140, Fortaleza, Brazil
    D. Weaver
  20. Observatoire Aquitain des Sciences de l'Univers, 33270, Floirac, France
    J.-F. Lecampion
  21. Observatorio Astronómico, Universidad Nacional de Asunción, 2169, Paraguay
    F. Doncel & T. Momiyama
  22. Observatorio Astronómico Los Molinos, Facultad de Ciencias, 11400, Montevideo, Uruguay
    G. Tancredi

Authors

  1. B. Sicardy
  2. A. Bellucci
  3. E. Gendron
  4. F. Lacombe
  5. S. Lacour
  6. J. Lecacheux
  7. E. Lellouch
  8. S. Renner
  9. S. Pau
  10. F. Roques
  11. T. Widemann
  12. F. Colas
  13. F. Vachier
  14. R. Vieira Martins
  15. N. Ageorges
  16. O. Hainaut
  17. O. Marco
  18. W. Beisker
  19. E. Hummel
  20. C. Feinstein
  21. H. Levato
  22. A. Maury
  23. E. Frappa
  24. B. Gaillard
  25. M. Lavayssière
  26. M. Di Sora
  27. F. Mallia
  28. G. Masi
  29. R. Behrend
  30. F. Carrier
  31. O. Mousis
  32. P. Rousselot
  33. A. Alvarez-Candal
  34. D. Lazzaro
  35. C. Veiga
  36. A. H. Andrei
  37. M. Assafin
  38. D. N. da Silva Neto
  39. C. Jacques
  40. E. Pimentel
  41. D. Weaver
  42. J.-F. Lecampion
  43. F. Doncel
  44. T. Momiyama
  45. G. Tancredi

Corresponding author

Correspondence toB. Sicardy.

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Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

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Sicardy, B., Bellucci, A., Gendron, E. et al. Charon's size and an upper limit on its atmosphere from a stellar occultation.Nature 439, 52–54 (2006). https://doi.org/10.1038/nature04351

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Editorial Summary

Charon among the stars

Stellar occultations, when a Solar System object passes between us and a star and blocks its light, are eagerly awaited by astronomers as they provide a chance to make measurements that are not normally possible. It had been 25 years since a solitary observation of a stellar occultation by Pluto's moon Charon. But on 11 July 2005 another occurred and this time observatories across South America were ideally placed to track it. The resulting haul of data has been used to obtain an accurate measure of Charon's radius, of close to 605 km, and to establish an upper limit (a rather low one) on the density of its atmosphere. Visit tinyurl.com/9c56s for a QuickTime movie of the event.

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