Volume 639, July 2020
|Number of page(s)||11|
|Section||Planets and planetary systems|
|Published online||09 July 2020|
HDO and SO2 thermal mapping on Venus
V. Evidence for a long-term anti-correlation
LESIA, Observatoire de Paris, PSL University, CNRS, Sorbonne Université, Université de Paris,
2 SwRI, Div. 15, San Antonio, TX 78228, USA
3 LATMOS/IPSL, UVSQ Université Paris-Saclay, Sorbonne Université, CNRS, 78280 Guyancourt, France
4 Kyoto Sangyo University, Kyoto 603-8555, Japan
5 LMD/IPSL, Sorbonne University, ENS, PSL University, Ecole Polytechnique, University Paris Saclay, CNRS, 75252 Paris Cedex 05, France
6 Planetary Science Laboratory, University of Michigan, Ann Arbor MI 48109-2143, USA
7 Zentrum fuer Astronomie und Astrophysik, Technische Universitaet Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
8 Jet Propulsion Laboratory, Pasadena, CA 91109, USA
9 Hokkaido Information University, Hokkaido 069-8585, Japan
10 Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064, USA
Accepted: 19 May 2020
Since January 2012, we have been monitoring the behavior of sulfur dioxide and water on Venus, using the Texas Echelon Cross-Echelle Spectrograph imaging spectrometer at the NASA InfraRed Telescope Facility (IRTF, Mauna Kea Observatory). Here, we present new data recorded in February and April 2019 in the 1345 cm−1 (7.4 μm) spectral range, where SO2, CO2, and HDO (used as a proxy for H2O) transitions were observed. The cloud top of Venus was probed at an altitude of about 64 km. As in our previous studies, the volume mixing ratio (vmr) of SO2 was estimated using the SO2/CO2 line depth ratio of weak transitions; the H2O volume mixing ratio was derived from the HDO/CO2 line depth ratio, assuming a D/H ratio of 200 times the Vienna standard mean ocean water. As reported in our previous analyses, the SO2 mixing ratio shows strong variations with time and also over the disk, showing evidence for the formation of SO2 plumes with a lifetime of a few hours; in contrast, the H2O abundance is remarkably uniform over the disk and shows moderate variations as a function of time. We have used the 2019 data in addition to our previous dataset to study the long-term variations of SO2 and H2O. The data reveal a long-term anti-correlation with a correlation coefficient of −0.80; this coefficient becomes −0.90 if the analysis is restricted to the 2014–2019 time period. The statistical analysis of the SO2 plumes as a function of local time confirms our previous result with a minimum around 10:00 and two maxima near the terminators. The dependence of the SO2 vmr with respect to local time shows a higher abundance at the evening terminator with respect to the morning. The dependence of the SO2 vmr with respect to longitude exhibits a broad maximum at 120–200° east longitudes, near the region of Aphrodite Terra. However, this trend has not been observed by other measurements and has yet to be confirmed.
Key words: planets and satellites: atmospheres / planets and satellites: terrestrial planets / infrared: planetary systems
© T. Encrenaz et al. 2020
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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