Letter | Published:

Haze heats Pluto’s atmosphere yet explains its cold temperature

Nature volume 551, pages 352355 (16 November 2017) | Download Citation


Pluto’s atmosphere is cold and hazy1,2,3. Recent observations1 have shown it to be much colder than predicted theoretically4, suggesting an unknown cooling mechanism1. Atmospheric gas molecules, particularly water vapour, have been proposed as a coolant; however, because Pluto’s thermal structure is expected to be in radiative–conductive equilibrium4,5,6,7,8,9, the required water vapour would need to be supersaturated by many orders of magnitude under thermodynamic equilibrium conditions9. Here we report that atmospheric hazes, rather than gases, can explain Pluto’s temperature profile. We find that haze particles have substantially larger solar heating and thermal cooling rates than gas molecules, dominating the atmospheric radiative balance from the ground to an altitude of 700 kilometres, above which heat conduction maintains an isothermal atmosphere. We conclude that Pluto’s atmosphere is unique among Solar System planetary atmospheres, as its radiative energy equilibrium is controlled primarily by haze particles instead of gas molecules. We predict that Pluto is therefore several orders of magnitude brighter at mid-infrared wavelengths than previously thought—a brightness that could be detected by future telescopes.

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We thank Y. Yung, B. Bézard, E. Lellouch, M. Liang, X. Zhu and P. Gao for discussions. X.Z. acknowledges partial support from NASA Solar System Workings grant NNX16AG08G. D.F.S. acknowledges partial support from NASA’s New Horizons Mission. H.I. acknowledges support from NASA Cassini Data Analysis grant NNX14AF61G and NASA Exoplanet Research grant NNX15AQ73G.

Author information


  1. Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, California 95064, USA

    • Xi Zhang
  2. Department of Earth & Planetary Sciences and Physics & Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA

    • Darrell F. Strobel
  3. SETI Institute, 189 North Bernardo Avenue, Suite 100, Mountain View, California 94043, USA

    • Hiroshi Imanaka
  4. NASA Ames Research Center, Moffett Field, California 94035, USA

    • Hiroshi Imanaka


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X.Z. conceived the research, performed the calculations and wrote the manuscript. D.F.S. provided the New Horizons data and the gas-only model and assisted with analysis. H.I. provided the refractive indices of haze particles. D.F.S. and H.I. contributed to manuscript writing.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Xi Zhang.

Reviewer Information Nature thanks R. West and Y. Yung for their contribution to the peer review of this work.

Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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