Published January 11, 2022 | Published + Accepted Version + Supplemental Material

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A bimodal distribution of haze in Pluto's atmosphere

Creators: Fan, Siteng; Gao, Peter; Zhang, Xi; Adams, Danica J.; Kutsop, Nicholas W.; Bierson, Carver J.; Liu, Chao; Yang, Jiani; Young, Leslie A.; Cheng, Andrew F.; Yung, Yuk L.

Abstract

Pluto, Titan, and Triton make up a unique class of solar system bodies, with icy surfaces and chemically reducing atmospheres rich in organic photochemistry and haze formation. Hazes play important roles in these atmospheres, with physical and chemical processes highly dependent on particle sizes, but the haze size distribution in reducing atmospheres is currently poorly understood. Here we report observational evidence that Pluto's haze particles are bimodally distributed, which successfully reproduces the full phase scattering observations from New Horizons. Combined with previous simulations of Titan's haze, this result suggests that haze particles in reducing atmospheres undergo rapid shape change near pressure levels ~0.5 Pa and favors a photochemical rather than a dynamical origin for the formation of Titan's detached haze. It also demonstrates that both oxidizing and reducing atmospheres can produce multi-modal hazes, and encourages reanalysis of observations of hazes on Titan and Triton.

Additional Information

© The Author(s) 2022. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Received 22 September 2021; Accepted 22 November 2021; Published 11 January 2022. We thank William M. Grundy for sharing the LEISA data, Michael L. Wong and Xue Feng for improving figure representations, and Yan Wu for comments. P.G. is supported by NASA Hubble Fellowship grant HST-HF2-51456.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. X.Z. is supported by NASA Solar System Workings Grant 80NSSC19K0791. A.F.C. is supported by NASA under the New Horizons Project. Data availability: The New Horizons observations are available on NASA PDS (https://pds-smallbodies.astro.umd.edu/data_sb/missions/newhorizons/index.shtml). The measured haze optical properties are in Khare et al. 38. The processed observations, including the extinction and scattering intensities, are attached in the Supplementary Information. The retrieved parameters describing haze morphology and corresponding scattering properties are also attached in the Supplementary Information. Source data are provided with this paper. Code availability: The data processing procedure is described step by step in the Methods. The Python package emcee for implementing MCMC is available at https://emcee.readthedocs.io. The haze scattering model is described in the appendix of Tomasko et al.10. The sphere pixelation tool is available at https://healpix.sourceforge.io. Author Contributions: S.F. conducted the data analysis, performed the calculations, and wrote the manuscript. S.F., P.G., X.Z., and Y.L.Y. conceived and designed the research. P.G. and D.J.A. provided the microphysical model. P.G. and C.L. provided the aggregate scattering model. X.Z. originated the idea of bi-modality. N.W.K. and C.J.B. contributed to the analysis of MVIC data. J.Y. contributed to interpreting and presenting the retrieval results. L.A.Y. and A.F.C provided insights into interpreting New Horizons observations. All authors contributed to the manuscript writing. The authors declare no competing interests. Peer review information: Nature Communications thanks Kathleen Mandt and the anonymous reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

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