Uranus and Neptune in the Mid-Infrared: Recent Findings from VLT-VISIR and Future Opportunities with JWST-MIRI
Authors: Roman Michael T , Fletcher Leigh N. , Orton Glenn S. , Rowe-Gurney Naomi , Moses Julianne , Greathouse Thomas K. , Irwin Patrick G. J. , Kasaba Yasumasa , Fujiyoshi Takuya , Hammel Heidi B. , de Pater Imke , Antunano Arrate , Sinclair James , Melin Henrik , Bardet Deborah 
Published: September 2022

&lt;p&gt;&lt;strong&gt;In this talk, we present highlights from our recent analyses of mid-infrared observations of Uranus and Neptune, and we look ahead to anticipated discoveries from the James Webb Space Telescope. &amp;#160;&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;Drawing from a combination of archival and recent ground-based imaging and spectroscopy, we examine the spatial structure and trends of mid-infrared emission from the ice giant atmospheres.&amp;#160; &lt;strong&gt;We report on surprising temporal variability in the atmosphere of Neptune&lt;/strong&gt; (see Figure 1) with an unexpected decline in stratospheric temperatures since at least 2003. &amp;#160;Recent VLT-VISIR imaging and spectroscopy are presented, revealing how this trend has progressed.&lt;/p&gt;
&lt;p&gt;In contrast, we show that no evidence yet exists of long-term thermal changes in Uranus&amp;#8217; stratosphere, but mid-IR observations of Uranus are still extremely limited. &lt;strong&gt;The observed spatial structure of Uranus&amp;#8217; mid-infrared emission is intriguing&lt;/strong&gt; (Figure 2), as it is inconsistent with simple models of the atmospheric circulation and/or chemistry and &lt;strong&gt;its physical interpretation remains unclear.&lt;/strong&gt; We share recent observations from VLT-VISIR and express the need for continued ground-based imaging for both Uranus and Neptune.&lt;/p&gt;
&lt;p&gt;Finally, we discuss how the &lt;strong&gt;James Webb Space Telescope MIRI observations &lt;/strong&gt;will help greatly advance our understanding of the ice giants in the years ahead&lt;strong&gt;.&lt;/strong&gt; In particular, given its supreme sensitivity compared to ground-based observations, JWST-MIRI observations will resolve the nature of Uranus stratospheric thermal/chemical structure and reveal how temperature and chemical abundances change with the seasons in the atmospheres of both ice giants.&lt;/p&gt;
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&lt;p&gt;&lt;strong&gt;Figure 1:&lt;/strong&gt; &lt;em&gt;Observed changes in Neptune&amp;#8217;s thermal-infrared brightness, a measure of temperature in Neptune&amp;#8217;s atmosphere. The plot shows the relative change in the thermal-infrared brightness from Neptune&amp;#8217;s stratosphere with time for all existing images taken by ground-based telescopes. Brighter images are interpreted as warmer. Corresponding thermal-infrared images (top) at wavelengths of ~12 &amp;#181;m show Neptune&amp;#8217;s appearance in 2006, 2009, 2018 (observed by the European Southern Observatory&amp;#8217;s Very Large Telescope VISIR instrument), and 2020 (observed by Subaru&amp;#8217;s COMICS instrument). The south pole appears to have become dramatically warmer in just the past few years.&amp;#160;&lt;/em&gt;&lt;/p&gt;
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&lt;p&gt;&lt;strong&gt;Figure 2: &lt;/strong&gt;&lt;em&gt;Uranus' 13-micron images from VLT-VISIR in 2009 and 2018, with enhanced emission from high latitudes.&amp;#160; From current ground-based observations alone, it is unclear whether the enhanced radiances are due to greater temperatures or enhance acetylene abundances, but JWST will solve this mystery.&amp;#160; &lt;br /&gt;&lt;/em&gt;&lt;/p&gt;
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