(top) Comparison of the temperature profiles and structure of the atmospheres of Titan and Earth. Vertical bars at left show the regions probed by Cassini instruments (Ion and Neutral Mass Spectrometer, INMS; CAssini Plasma Spectrometer, CAPS; Radio and Plasma Wave Science, RPWS; UltraViolet Imaging Spectrometer, UVIS; Imaging Science Subsystem, ISS; Visual and Infrared Mapping Spectrometer, VIMS; Composite InfraRed Spectrometer, CIRS), the Huygens Gas Chromatograph Mass Spectrometer (GCMS), and the Atacama Large Millimeter/submillimeter Array (ALMA) telescope. (bottom) Similar to the cycling of water on Earth, Titan's troposphere hosts the hydrological cycle of methane between the surface and on atmosphere. Irreversible loss of methane in the thermosphere suggests that a methane replenishment mechanism is necessary.

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... hosts the most Earth-like atmosphere in the solar system. Similarities include the atmospheric structure ( Fulchignoni et al. 2005) (Figure 1), a nitrogen-dominated composition (95% N 2 , 4% CH 4 , and 1% trace species at the surface), and a surface pressure of 1.5 bar. The photolytic destruction of atmospheric methane initiates a chain of photochemical reactions responsible for the plethora of organic species that make up the haze observed by CassiniHuygens and ground-based facilities ( Marten et al. 2002;Gurwell 2004;Ali et al. 2013;Cordiner et al. 2014Cordiner et al. , 2015Cordiner et al. , 2018Cordier & Carrasco 2019;Molter et al. 2016;Desai et al. 2017;Lai et al. 2017;Palmer et al. 2017;Teanby et al. 2018;Lombardo et al. 2019;Thelen et al. 2019bThelen et al. ,a, 2020Nixon et al. 2020). ...

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... hosts the most Earth-like atmosphere in the solar system. Similarities include the atmospheric structure ( Fulchignoni et al. 2005) (Figure 1), a nitrogen-dominated composition (95% N 2 , 4% CH 4 , and 1% trace species at the surface), and a surface pressure of 1.5 bar. The photolytic destruction of atmospheric methane initiates a chain of photochemical reactions responsible for the plethora of organic species that make up the haze observed by CassiniHuygens and ground-based facilities ( Marten et al. 2002;Gurwell 2004;Ali et al. 2013;Cordiner et al. 2014Cordiner et al. , 2015Cordiner et al. , 2018Cordier & Carrasco 2019;Molter et al. 2016;Desai et al. 2017;Lai et al. 2017;Palmer et al. 2017;Teanby et al. 2018;Lombardo et al. 2019;Thelen et al. 2019bThelen et al. ,a, 2020Nixon et al. 2020). ...

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... thank the broader Titan community for supporting the submission of a white paper of similar content to the 2023-2032 Decadal Survey. We also thank Caleb Heidel (JHU APL) for graphical contributions to Figure 1. S.M.M. acknowledges support from JHU APL and Cassini Data Analysis and Participating Scientst Program (CDAP) grant #80NSSC19K0888. ...