Unexpected increase of the deuterium to hydrogen ratio in the Venus mesosphere
Vandaele, Ann Carine; Robert, Séverine; Chamberlain, Sarah; Trompet, Loïc; Willame, Yannick; Mahieux, Arnaud; Piccialli, Arianna; Pereira, Nuno; Nakagawa, Hiromu; Koyama, Shungo; Maggiolo, Romain; Karyu, Hiroki; Viscardy, Sébastien; Cessateur, Gaël; Yelle, Roger Vincent; Erwin, Justin Tyler; Ubukata, Soma
Belgium, United States, Japan
Abstract
Studying Venus's HDO and H2O sheds light on its water history. The HDO/H2O ratio in its bulk atmosphere, 120 times Earth's, suggests a significantly wetter past for Venus. Our study analyzes mesospheric (70 to 110 km) temperature, H2O, and HDO profiles taken in solar occultation by SOIR/Venus Express. We observe increasing relative abundances of both isotopologues and a significant D/H ratio rise with altitude. This finding challenges previous assumptions about upper-mesosphere H and D abundances available for escape, impacting atmospheric evolution models. We propose a cycle mechanism involving water fractionation during condensation into the sulfur-based aerosols, evaporation, and transport in the mesosphere between warm and cold regions to explain our finding, which is consistent with the observed SO2 inversion layer.