Re-analysis of Phosphine in Venus' Clouds

Abstract

We first respond to two points raised by Villanueva et al. We show the JCMT discovery spectrum of PH3 can not be re-attributed to SO2, as the line width is larger than observed for SO2 features, and the required abundance would be an extreme outlier. The JCMT spectrum is also consistent with our simple model, constant PH3-abundance with altitude, with no discrepancy in line profile (within data limits); reconciliation with a full photochemical model is the subject of future work. Section 2 presents initial results from re-processed ALMA data. Villanueva et al. noted an issue with bandpass calibration. They have worked on a partially re-processed subset of the ALMA data, so we note where their conclusions, and those of Greaves et al., are now superseded. To summarise: we recover PH3 in Venus' atmosphere with ALMA (~5σ confidence). Localised abundance appears to peak at ~5-10 parts-per-billion (ppb), with suggestions of spatial variation. Advanced data-products suggest a planet-averaged PH3 abundance ~1-4 ppb, lower than from the earlier ALMA processing (which indicated 7+ ppb). The ALMA data are reconcilable with the JCMT detection (~20 ppb) if there is order-of-magnitude temporal variation; more advanced processing of the JCMT data is underway to check methods. Independent PH3 measurements suggest possible altitude dependence (under ~5 ppb at 60+ km, up to ~100 ppb at 50+ km; see Section 2: Conclusions.). Given that both ALMA and JCMT were working at the limit of observatory capabilities, new spectra should be obtained. The ALMA data in-hand are no longer limited by calibration, but spectral ripples still exist, probably due to size and brightness of Venus in relation to the primary beam. Further, spatial ripples are present, potentially reducing significance of real narrow spectral features.

Response to the Matters Arising: "No phosphine in the atmosphere of Venus" by G. Villanueva et al., preprint at arXiv:2010.14305; v2 contains updated values and additional technical details

References in corpus (8)

• Phosphine Gas in the Cloud Decks of Venus
• No evidence of phosphine in the atmosphere of Venus by independent analyses
• Venus' Mass Spectra Show Signs of Disequilibria in the Middle Clouds
• A stringent upper limit of the PH${}_3$ abundance at the cloud top of Venus
• Claimed detection of PH${}_3$ in the clouds of Venus is consistent with mesospheric SO${}_2$
• The statistical reliability of 267 GHz JCMT observations of Venus: No significant evidence for phosphine absorption
• On the Robustness of Phosphine Signatures in Venus' Clouds
• Revisiting the Sulfur-Water Chemical System in the Middle Atmosphere of Venus

Cited by in corpus (10)

• No evidence of phosphine in the atmosphere of Venus by independent analyses
• Phosphine in the Venusian Atmosphere: A Strict Upper Limit from SOFIA GREAT Observations
• On the Robustness of Phosphine Signatures in Venus' Clouds
• Low levels of sulphur dioxide contamination of Venusian phosphine spectra
• Venus' Atmospheric Chemistry and Cloud Characteristics Are Compatible with Venusian Life
• Large Interferometer For Exoplanets (LIFE): VIII. Where is the phosphine? Observing exoplanetary PH3 with a space based MIR nulling interferometer
• Astrobiological Potential of Venus Atmosphere Chemical Anomalies and Other Unexplained Cloud Properties
• Constraints on the production of phosphine by Venusian volcanoes
• Venusian phosphine: a 'Wow!' signal in chemistry?
• Necessary Conditions for Earthly Life Floating in the Venusian Atmosphere