[Paper Review] Is Phosphine in the Mass Spectra from Venus' Clouds?

Rakesh Mogul, S. S. Limaye+2 more|arXiv (Cornell University)|Sep 27, 2020

Planetary Science and Exploration4 citations

TL;DR

This study re-analyzes Pioneer-Venus Large Probe Neutral Mass Spectrometer (LNMS) data from Venus' clouds (50–60 km altitude) to investigate the presence of phosphorus compounds, specifically phosphine (PH₃). It finds evidence supporting phosphine's existence in the cloud layer, though its origin remains unexplained, contributing to ongoing debate about potential atmospheric biosignatures on Venus.

ABSTRACT

Considering the implications of the reported single spectral line detection of phosphine (PH3) by Greaves et al., we were inspired to re-examine data obtained from the Pioneer-Venus Large Probe Neutral Mass Spectrometer (LNMS) to search for evidence of phosphorus compounds. The LNMS obtained masses of neutral gases (and their fragments) at different altitudes within Venus' clouds. Published mass spectral data correspond to gases at altitudes of 50-60 km, or within the lower and middle clouds of Venus - which has been identified as a potential habitable. We find that LMNS data support the presence of phosphine; although, the origins of phosphine remain unknown.

Motivation & Objective

• To re-express and re-analyze published neutral mass spectrometry data from the Pioneer-Venus Large Probe to search for phosphorus-bearing compounds.
• To assess whether the reported detection of phosphine in Venus' atmosphere is supported by independent, pre-existing in situ measurements.
• To evaluate the presence of phosphine in the 50–60 km altitude range, a region considered potentially habitable.
• To contribute to the scientific debate on potential biosignatures in Venus' atmosphere by examining historical data.

Proposed method

• Re-analyzing mass spectral data collected by the Pioneer-Venus Large Probe Neutral Mass Spectrometer (LNMS) during its descent through Venus' cloud deck.
• Focusing on mass-to-charge ratios corresponding to phosphine (PH₃) and its potential fragment ions.
• Comparing observed ion intensities at 50–60 km altitude with expected signals from known atmospheric constituents.
• Assessing spectral features consistent with PH₃ based on molecular mass and fragmentation patterns.
• Using published LNMS data from the lower and middle cloud layers to evaluate signal consistency with phosphine.

Experimental results

Research questions

• RQ1 Does the Pioneer-Venus LNMS data contain detectable signals consistent with phosphine (PH₃) in Venus' cloud layer?
• RQ2 Are there mass spectral features in the LNMS data that match the expected m/z values for PH₃ and its fragments?
• RQ3 Can the presence of phosphine in the 50–60 km altitude range be supported by independent in situ measurements from the Pioneer-Venus mission?
• RQ4 What implications does the potential detection of phosphine have for the habitability and atmospheric chemistry of Venus?

Key findings

• The LNMS data from the 50–60 km altitude range show spectral features consistent with the presence of phosphine (PH₃).
• The observed signals align with the expected m/z values for PH₃ and its fragment ions, supporting its potential detection.
• No definitive identification of phosphorus compounds was made in earlier analyses of the same data, indicating the need for re-evaluation.
• The presence of phosphine in the cloud layer remains unexplained, as no known abiotic processes on Venus are currently sufficient to account for its formation.