Hazy Blue Worlds: A Holistic Aerosol Model for Uranus and Neptune, Including Dark Spots

PGJ Irwin*, Nicholas A Teanby, LN Fletcher, D Toledo, GS Orton, MH Wong, MT Roman, S Perez-Hoyos, A James, J Dobinson

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

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Abstract

We present a reanalysis (using the Minnaert limb-darkening approximation) of visible/near-infrared (0.3–2.5 μm) observations of Uranus and Neptune made by several instruments. We find a common model of the vertical aerosol distribution i.e., consistent with the observed reflectivity spectra of both planets, consisting of: (a) a deep aerosol layer with a base pressure >5–7 bar, assumed to be composed of a mixture of H2S ice and photochemical haze; (b) a layer of photochemical haze/ice, coincident with a layer of high static stability at the methane condensation level at 1–2 bar; and (c) an extended layer of photochemical haze, likely mostly of the same composition as the 1–2-bar layer, extending from this level up through to the stratosphere, where the photochemical haze particles are thought to be produced. For Neptune, we find that we also need to add a thin layer of micron-sized methane ice particles at ∼0.2 bar to explain the enhanced reflection at longer methane-absorbing wavelengths. We suggest that methane condensing onto the haze particles at the base of the 1–2-bar aerosol layer forms ice/haze particles that grow very quickly to large size and immediately “snow out” (as predicted by Carlson et al. (1988), https://doi.org/10.1175/1520-0469(1988)045<2066:CMOTGP>2.0.CO;2), re-evaporating at deeper levels to release their core haze particles to act as condensation nuclei for H2S ice formation. In addition, we find that the spectral characteristics of “dark spots”, such as the Voyager-2/ISS Great Dark Spot and the HST/WFC3 NDS-2018, are well modelled by a darkening or possibly clearing of the deep aerosol layer only.
Original languageEnglish
Article numbere2022JE007189
Number of pages44
JournalJournal of Geophysical Research: Planets
Volume127
Issue number6
Early online date23 May 2022
DOIs
Publication statusPublished - 4 Jun 2022

Bibliographical note

Funding Information:
We are grateful to the United Kingdom Science and Technology Facilities Council for funding this research (Irwin: ST/S000461/1, Teanby: ST/R000980/1). Glenn Orton was supported by funding to the Jet Propulsion Laboratory, California Institute of Technology, under contract 80NM0018D0004 with the National Aeronautics and Space Administration (NASA). Michael H. Wong and Glenn Orton received support for program GO/DD‐13937 and related programs from NASA through a grant from the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astroniomy, Inc. (AURA) under NASA contract NAS5‐26555. Leigh Fletcher and Mike Roman were supported by a European Research Council Consolidator Grant (under the European Union's Horizon 2020 research and innovation programme, grant agreement No 723890) at the University of Leicester. Santiago Pérez‐Hoyos is supported by grant PID2019‐109467GB‐I00Z, funded by MCIN/AEI/10.13039/501100011033. We are also grateful for the assistance of Larry Sromovsky and Pat Fry in locating and reading the HST/STIS data. We are also grateful to the PDS Ring‐Moon Systems Node's OPUS search service for providing access to the Voyager‐2 ISS images. Finally, the Gemini/NIFS observations used were obtained at the international Gemini Observatory, a program of NSF's NOIRLab, which is managed by AURA under a cooperative agreement with the National Science Foundation on behalf of the Gemini Observatory partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). This work was enabled by the location of the Gemini and NASA IRTF telescopes within the Maunakea Science Reserve, adjacent to the summit of Maunakea. We are grateful for the privilege of observing Uranus and Neptune from a place that is unique in both its astronomical qualtiy and its cultural significance.

Funding Information:
We are grateful to the United Kingdom Science and Technology Facilities Council for funding this research (Irwin: ST/S000461/1, Teanby: ST/R000980/1). Glenn Orton was supported by funding to the Jet Propulsion Laboratory, California Institute of Technology, under contract 80NM0018D0004 with the National Aeronautics and Space Administration (NASA). Michael H. Wong and Glenn Orton received support for program GO/DD-13937 and related programs from NASA through a grant from the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astroniomy, Inc. (AURA) under NASA contract NAS5-26555. Leigh Fletcher and Mike Roman were supported by a European Research Council Consolidator Grant (under the European Union's Horizon 2020 research and innovation programme, grant agreement No 723890) at the University of Leicester. Santiago Pérez-Hoyos is supported by grant PID2019-109467GB-I00Z, funded by MCIN/AEI/10.13039/501100011033. We are also grateful for the assistance of Larry Sromovsky and Pat Fry in locating and reading the HST/STIS data. We are also grateful to the PDS Ring-Moon Systems Node's OPUS search service for providing access to the Voyager-2 ISS images. Finally, the Gemini/NIFS observations used were obtained at the international Gemini Observatory, a program of NSF's NOIRLab, which is managed by AURA under a cooperative agreement with the National Science Foundation on behalf of the Gemini Observatory partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). This work was enabled by the location of the Gemini and NASA IRTF telescopes within the Maunakea Science Reserve, adjacent to the summit of Maunakea. We are grateful for the privilege of observing Uranus and Neptune from a place that is unique in both its astronomical qualtiy and its cultural significance.

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© 2022. The Authors.

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