P092-04
Challenges to the retrieval of PH3 from ALMA & JCMT observations
Friday, 11 December 2020: 10:42
Virtual
Geronimo Villanueva1, M Cordiner1, Patrick GJ Irwin2, Imke De Pater3, Bryan J Butler4, Mark A Gurwell5, Stefanie N Milam1, Conor A Nixon1, Statia Luszcz-Cook6, Colin F Wilson7, Vincent Kofman8, Giuliano Liuzzi8, Sara Faggi9, Thomas Fauchez10, Manuela Lippi9, Richard Cosentino11, Alexander E Thelen10, Arielle Moullet12, Paul Hartogh13, Edward Mischel Molter14, Steven B Charnley1, Giada N Arney1, Avi Mandell1, Nicolas Biver15, Ann Carine Vandaele16, Katherine de Kleer17 and Ravi Kopparapu18, (1)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (2)University of Oxford, Oxford, United Kingdom, (3)Univ California Berkeley, Berkeley, CA, United States, (4)National Radio Astronomy Observatory, Socorro, NM, United States, (5)Smithsonian Astrophysical Obs., Cambridge, MA, United States, (6)Columbia University, New York, United States, (7)Univ Oxford, Oxford, United Kingdom, (8)AU / NASA Goddard Space Flight Center, Greenbelt, United States, (9)AU / NASA Goddard Space Flight Center, Greenbelt, MD, United States, (10)USRA / NASA Goddard Space Flight Center, Greenbelt, MD, United States, (11)UMD / NASA Goddard Space Flight Center, Greenbelt, MD, United States, (12)SOFIA/USRA, Moffett Field, CA, United States, (13)MPI for Solar System Research, Katlenburg-Lindau, Germany, (14)University of California, Berkeley, Berkeley, CA, United States, (15)Observatoire de Paris, Paris, France, (16)Royal Belgian Institute for Space Aeronomy, Brussels, Belgium, (17)California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, CA, United States, (18)NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD, United States
Abstract:
Phosphine (PH3) has been recently reported to be present in the atmosphere of Venus (Greaves et at. 2020), as determined from radio observations with the James Clerk Maxwell Telescope (JCMT) and the Atacama Large Millimeter/submillimeter Array (ALMA). We find that the spectral feature identified with JCMT and ascribed to PH3 could instead be explained employing plausible mesospheric SO2 abundances (~100 ppbv), while the identification of PH3 in the ALMA spectra as presented was affected by severe spectral passband calibration issues. We have independently calibrated and analyzed the raw ALMA data using different interferometric analysis tools, and in all cases, we do not detect the PH3 spectral line. Furthermore, our radiative transfer models show that for a PH3 signature to be observable in either the ALMA or JCMT spectra, phosphine needs to be present in the atmosphere of Venus at altitudes above 70 km, in contrast with the suggested altitudes of 55-65 km from the reported photochemical network. From our analysis of these data, we ultimately determine sensitive upper-limits for the mesospheric abundance of PH3 in Venus.
