Hazy blue worlds: A holistic aerosol model for Uranus and Neptune, including Dark Spots. (arXiv:2201.04516v1 [astro-ph.EP])

Hazy blue worlds: A holistic aerosol model for Uranus and Neptune, including Dark Spots. (arXiv:2201.04516v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Irwin_P/0/1/0/all/0/1">Patrick G.J. Irwin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Teanby_N/0/1/0/all/0/1">Nicholas A. Teanby</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fletcher_L/0/1/0/all/0/1">Leigh N. Fletcher</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Toledo_D/0/1/0/all/0/1">Daniel Toledo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Orton_G/0/1/0/all/0/1">Glenn S. Orton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wong_M/0/1/0/all/0/1">Michael H. Wong</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Roman_M/0/1/0/all/0/1">Michael T. Roman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Perez_Hoyos_S/0/1/0/all/0/1">Santiago Perez-Hoyos</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+James_A/0/1/0/all/0/1">Arjuna James</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dobinson_J/0/1/0/all/0/1">Jack Dobinson</a>

We present a reanalysis (using the Minnaert limb-darkening approximation) of
visible/near-infrared (0.3 – 2.5 micron) observations of Uranus and Neptune
made by several instruments. We find a common model of the vertical aerosol
distribution that is consistent with the observed reflectivity spectra of both
planets, consisting of: 1) a deep aerosol layer with a base pressure >7 bar,
assumed to be composed of a mixture of H2S ice and photochemical haze; 2) a
layer of photochemical haze, trapped in a layer of high static stability at the
methane condensation level at 1-2 bar; and 3) an extended layer of
photochemical haze, likely 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), 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
clearing of the deep aerosol layer only.

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