No evidence of phosphine in the atmosphere of Venus from independent analyses

Abstract

The detection of phosphine (PH3) in the atmosphere of Venus has been recently reported employing mm-wave radio observations 1 , hereafter G2020. In this report, we identify several fundamental issues in the analysis and interpretation of the spectroscopic data, which would mean that the detection PH3 is not supported by our analysis of the data.The measurements target the fundamental first rotational transition of PH3 (J=1-0) at 266.944513 GHz, which was observed with the James Maxwell Clark Telescope (JCMT) in June 2017 and with the Atacama Large Millimeter/submillimeter Array (ALMA) in March 2019. This line is very close to the SO2 (J=309,21-318,24) transition at 266.943329 GHz (only 1.3 km/s away from the PH3 line) and therefore this SO2 line represents a serious source of contamination. The presented JCMT and ALMA datasets as presented in G2020 are at spectral resolutions comparable to the velocity separation of the two lines, and the line cores are several km/s in width, which does not permit spectroscopic separation of these two species.To explore the hypothesis that the observed 267 GHz feature is SO2, and not PH3, we employed the same VIRA45 temperature/pressure (T/P) profile used by G2020 ("extended Data Figure 8") and the G2020 SO2 profile ("extended Data Figure 9"). See further information about plausible Venus SO2 abundances and known variability in S1. As shown in Figure 1, we can fully explain the claimed "PH3" feature with their SO2 profile. For these simulations, we employed three independent radiative transfer analyses: the Planetary Spectrum Generator (PSG, https://psg.gsfc.nasa.gov) 2 , the Non-linear optimal Estimator for MultivariatE spectral analySIS (NEMESIS) 3 and the CfA planetary modeling tool 4 . The PSG radiative transfer analysis included the latest HITRAN SO2 line parameters for a CO2 atmosphere 5 , a layer-by-layer line-by-line study, and a full disk sampling scheme with 10 concentric rings. The NEMESIS analysis was also performed in line-by-line mode, and used the same line data with a 5-point Gauss-Lobatto disc-integration scheme. As described in G2020, there is some uncertainty in the line-shape parameters for the PH3 line in a CO2 atmosphere. HITRAN reports an air linewidth of 0.067 cm -1 /atm for this line, which could correspond to 0.12 cm -1 /atm for CO2 if we scale by the typical 1.8 scaling ratio observed for the SO2 lines 6 . G2020 employed the line shape for the NH3(J=1-0) line at 572.498160 GHz, which has a much greater linewidth of 0.2862 cm -1 /atm. This uncertainty in the linewidth has a dramatic impact on the inferred PH3 abundance, and our upper limit for the abundance of PH3 from these data (after removing SO2) ranges from < 5 ppb (3s) for 0.12 cm -1 /atm to < 12 ppb (3s) for 0.2862 cm -1 /atm (Figure 1). This upper-limit is consistent with the recent reports of non-detection of PH3 (< 5 ppb) at infrared wavelengths with TEXES/NASA-IRTF 7 .

Was Venus Ever Habitable? Constraints from a Coupled Interior–Atmosphere–Redox Evolution Model

“…Understanding past conditions on Venus may enable more robust interpretations of terrestrial exoplanet observations (Kane et al 2019;Lustig-Yaeger et al 2019b). Moreover, purported detections of phosphine in Venus's atmosphere and its possible biological origin (Bains et al 2021;Greaves et al 2021), while controversial (Encrenaz et al 2020;Snellen et al 2020;Akins et al 2021;Villanueva et al 2021), similarly highlight the need to better understand Venusian history, as does recent reanalysis of Pioneer Mass Spectrometer data that are suggestive of previously unknown chemical disequilibria in Venus's middle atmosphere (Mogul et al 2021).…”

Chemical complexity of phosphorous bearing species in various regions of the Interstellar medium

“…This discovery opened up a series of debates. Very recently, Villanueva et al (2020) question about the analysis and interpretation of the spectroscopic data used in Greaves et al (2020). These authors claimed that there is no PH 3 in Venus's atmosphere.…”

“…Our computed BE with H 2 SO 4 and Benzene is ∼ 2271 K and ∼ 3094 K, respectively. However,Snellen et al (2020) andVillanueva et al (2020) questioned about the identification ofGreaves et al…”

From Atmospheric Evolution to the Search of Species of Astrobiological Interest in the Solar System—Case Studies Using the Planetary Spectrum Generator

“…The non-detection of phosphine, as in Encrenaz et al [22], does not preclude the existence of phosphine on Venus. We must consider that only an upper limit of 7 ppb was derived and still has not confirmed [20,21,73]. One must also consider possible latitudinal, temporal and altitude variations in the abundance of phosphine.…”