Charon's radius and atmospheric constraints from observations of a stellar occultation (original) (raw)

Nature volume 439, pages 48–51 (2006)Cite this article

Abstract

The physical characteristics of Pluto and its moon, Charon, provide insight into the evolution of the outer Solar System. Although previous measurements have constrained the masses of these bodies1,2, their radii and densities have remained uncertain. The observation of a stellar occultation by Charon in 1980 established a lower limit on its radius of 600 km (ref. 3) (later refined to 601.5 km; ref. 4) and suggested a possible atmosphere4. Subsequent, mutual event modelling yielded a range of 600–650 km (ref. 5), corresponding to a density of 1.56 ± 0.22 g cm-3 (refs 2, 5). Here we report multiple-station observations of a stellar occultation by Charon. From these data, we find a mean radius of 606 ± 8 km, a bulk density of 1.72 ± 0.15 g cm-3, and rock-mass fraction 0.63 ± 0.05. We do not detect a significant atmosphere and place 3_σ_ upper limits on atmospheric number densities for candidate gases. These results seem to be consistent with collisional formation for the Pluto–Charon system in which the precursor objects may have been differentiated6, and they leave open the possibility of atmospheric retention by the largest objects in the outer Solar System.

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Acknowledgements

B.A.B., J.W.G. and T.T. are Guest Observers at Instituto de Astronomía, Universidad Católica del Norte, Antofagasta, Chile. We thank N. Vogt and M. Murphy of Universidad Católica del Norte for their expertise, assistance, and the use of their telescope at Cerro Armazones; G. Gutiérrez and F. Sánchez, telescope operators at Las Campanas; R. Carrasco, K. Volk (observers), and E. Wendroth (telescope operator) at Gemini South; M. Ottoboni and R. Campos at Pico Dos Dias; and C. Czelusniak, assistant observer from Universidade Estadual de Ponta Grossa. Full credits for Gemini Observatory are available at http://www.us-gemini.noao.edu/sciops/data/dataAcknowIndex.html. Support for this work was provided by NASA Planetary Astronomy. Additional support was provided by the Belgian Federal Office for Scientific, Technical and Cultural Affairs and the Flemish Ministry for Foreign Policy, European Affairs, Science and Technology.

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Authors and Affiliations

  1. Department of Earth, Atmospheric, and Planetary Sciences,
    A. A. S. Gulbis, J. L. Elliot, M. J. Person, E. R. Adams, S. D. Kern & E. A. Kramer
  2. Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139-4307, USA
    J. L. Elliot
  3. Lowell Observatory, Flagstaff, Arizona, 86001, USA
    J. L. Elliot
  4. Physics Department,
    B. A. Babcock
  5. Astronomy Department, Williams College, Williamstown, Massachusetts, 01267-2565, USA
    J. W. Gangestad, J. M. Pasachoff & S. P. Souza
  6. Instituto de Astronomía, Universidad Católica del Norte, Avda. Angamos 0610, Antofagasta, Chile
    B. A. Babcock, J. W. Gangestad & T. Tuvikene
  7. Departamento de Geociências, Universidade Estadual de Ponta Grossa, Paraná, Brazil
    M. Emilio
  8. Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena, Chile
    D. J. Osip
  9. Vrije Universiteit Brussel, Brussels, Belgium
    T. Tuvikene

Authors

  1. A. A. S. Gulbis
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  2. J. L. Elliot
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  3. M. J. Person
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  4. E. R. Adams
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  5. B. A. Babcock
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  6. M. Emilio
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  7. J. W. Gangestad
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  8. S. D. Kern
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  9. E. A. Kramer
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  10. D. J. Osip
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  11. J. M. Pasachoff
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  12. S. P. Souza
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  13. T. Tuvikene
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Corresponding author

Correspondence toA. A. S. Gulbis.

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Supplementary information

Supplementary Table

This lists the five sites from which we arranged to view the occultation of C313.2 by Charon and provides details about the observations. (DOC 41 kb)

Supplementary Discussion

This provides a complete description of how we established Charon’s radius and error bar (DOC 23 kb)

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Gulbis, A., Elliot, J., Person, M. et al. Charon's radius and atmospheric constraints from observations of a stellar occultation.Nature 439, 48–51 (2006). https://doi.org/10.1038/nature04276

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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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