Letters to Nature

Nature 393, 765-767 (25 June 1998) | doi:10.1038/31651; Received 12 February 1998; Accepted 14 April 1998

Global warming on Triton

J. L. Elliot1,2,3, H. B. Hammel1, L. H. Wasserman3, O. G. Franz3, S. W. McDonald1, M. J. Person1, C. B. Olkin3, E. W. Dunham3, J. R. Spencer3, J. A. Stansberry3, M. W. Buie3, J. M. Pasachoff4, B. A. Babcock5 & T. H. McConnochie4

  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. Lowell Observatory, Flagstaff, Arizona 86001, USA
  4. Astronomy Department, Williams College, Williamstown, Massachusetts 01267-2565, USA
  5. Physics Department, Williams College, Williamstown, Massachusetts 01267-2565, USA

Correspondence to: J. L. Elliot1,2,3 Correspondence and requests for materials should be addressed to J.L.E. at the Department of Earth, Atmospheric, and Planetary Sciences, MIT.

Triton, Neptune's largest moon, has been predicted to undergo significant seasonal changes that would reveal themselves as changes in its mean frost temperature1, 2, 3. But whether this temperature should at the present time be increasing, decreasing or constant depends on a number of parameters (such as the thermal properties of the surface, and frost migration patterns) that are unknown. Here we report observations of a recent stellar occultation by Triton which, when combined with earlier results, show that Triton has undergone a period of global warming since 1989. Our most conservative estimates of the rate of temperature and surface-pressure increase during this period imply that the atmosphere is doubling in bulk every 10 years—significantly faster than predicted by any published frost model for Triton2,3. Our result suggests that permanent polar caps on Triton play a dominant role in regulating seasonal atmospheric changes. Similar processes should also be active on Pluto.