Titan's ‘detached’ haze, seen in Voyager images in 1980 and 1981 and monitored by the Cassini Imaging Science Subsystem (ISS) during the period 2004–2017, provides a measure of seasonal activity in Titan’s mesosphere with observations over almost half of Saturn’s seasonal cycle. Here we report on retrieved haze extinction profiles that reveal a depleted layer (having a diminished aerosol content), visually manifested as a gap between the main haze and a thin, detached upper layer. Our measurements show the disappearance of the feature in 2012 and its reappearance in 2016, as well as details after the reappearance. These observations highlight the dynamical nature of the detached haze. The reappearance seems congruent with earlier descriptions by climate models but more complex than previously described. It occurs in two steps, first as haze reappearing at 450 ± 20 km and one year later at 510 ± 20 km. These observations provide additional tight and valuable constraints about the underlying mechanisms, especially for Titan's mesosphere, that control Titan's haze cycle.
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Research was supported by the Cassini-Huygens mission, a cooperative endeavour of NASA, ESA and ASI managed by JPL/Caltech under a contract with NASA. Part of this work was performed by the Jet Propulsion Laboratory, California Institute of Technology. Part of this work was done while R.A.W. was hosted at the Université de Reims Champagne-Ardenne with the support of the Région Champagne-Ardenne, and simultaneously with the support of the JPL Senior Research Scientist Leave programme. P.R. thanks the Agence Nationale de la Recherche (ANR Project ‘APOSTIC’ no. 11BS56002, France).
Supplementary Figures 1–3