Letters to Nature

Nature 424, 165-168 (10 July 2003) | doi:10.1038/nature01762; Received 28 February 2003; Accepted 27 May 2003

The recent expansion of Pluto's atmosphere

J. L. Elliot1,2,3, A. Ates4, B. A. Babcock5, A. S. Bosh3,6, M. W. Buie3, K. B. Clancy1, E. W. Dunham3, S. S. Eikenberry7, D. T. Hall8, S. D. Kern1, S. K. Leggett8, S. E. Levine9, D.-S. Moon7, C. B. Olkin3, D. J. Osip1,10, J. M. Pasachoff11, B. E. Penprase4, M. J. Person1, S. Qu12, J. T. Rayner13, L. C. Roberts, Jr8, C. V. Salyk1, S. P. Souza11, R. C. Stone9, B. W. Taylor3, D. J. Tholen14, J. E. Thomas-Osip1,10, D. R. Ticehurst11 & L. H. Wasserman3

  1. Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA
  2. Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA
  3. Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA
  4. Lowell Observatory, Flagstaff, Arizona 86001, USA
  5. Department of Physics & Astronomy, Pomona College, 610 N. College Avenue, Claremont, California 91711, USA
  6. Physics Department, Williams College, Williamstown, Massachusetts 01267-2565, USA
  7. Hopkins Observatory, Williams College, Williamstown, Massachusetts 01267-2565, USA
  8. Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, Massachusetts 02215, USA
  9. Department of Astronomy, 212 Space Sciences Building, Cornell University, Ithaca, New York 14853, USA
  10. The Boeing Company, 535 Lipoa Pkwy, Suite 200, Kihei, Hawaii 96753, USA
  11. US Naval Observatory, Flagstaff Station, PO Box 1149, Flagstaff, Arizona 86002-1149, USA
  12. NASA Infrared Telescope Facility, Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, Hawaii 96822, USA
  13. Present address: Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena, Chile.

Correspondence to: J. L. Elliot1,2,3 Email: jle@mit.edu

Stellar occultations—the passing of a relatively nearby body in front of a background star—can be used to probe the atmosphere of the closer body with a spatial resolution of a few kilometres (ref. 1). Such observations can yield the scale height, temperature profile, and other information about the structure of the occulting atmosphere. Occultation data acquired for Pluto's atmosphere in 1988 revealed a nearly isothermal atmosphere2 above a radius of approx1,215 km. Below this level, the data could be interpreted as indicating either an extinction layer or the onset of a large thermal gradient, calling into question the fundamental structure of this atmosphere. Another question is to what extent Pluto's atmosphere might be collapsing as it recedes from the Sun (passing perihelion in 1989 in its 248-year orbital period), owing to the extreme sensitivity of the equilibrium surface pressure to the surface temperature. Here we report observations at a variety of visible and infrared wavelengths of an occultation of a star by Pluto in August 2002. These data reveal evidence for extinction in Pluto's atmosphere and show that it has indeed changed, having expanded rather than collapsed, since 1988.