Issue |
A&A
Volume 676, August 2023
|
|
---|---|---|
Article Number | A135 | |
Number of page(s) | 11 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361/202142548 | |
Published online | 23 August 2023 |
Uncertainty in phosphine photochemistry in the Venus atmosphere prevents a firm biosignature attribution
1
Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt,
Rutherfordstraße 2,
12489
Berlin,
Germany
e-mail: wunderlich.fabian@googlemail.com
2
Zentrum für Astronomie und Astrophysik, Technische Universität Berlin,
Hardenbergstraße 36,
10623
Berlin,
Germany
3
Institut für Geologische Wissenschaften, Freie Universität Berlin,
Malteserstr. 74-100,
12249
Berlin,
Germany
Received:
29
October
2021
Accepted:
28
March
2023
Context. The possible detection of phosphine (PH3) in the clouds of Venus has raised the question as to which processes could produce such large abundances of PH3. Previous studies suggested that abiotic processes including photochemical production cannot explain the claimed PH3 concentrations. However, the photochemistry of phosphorus-bearing species in the atmosphere of Venus is not well known.
Aims. We aim to assess the abiotic production of PH3 considering the effect of uncertainties in the chemical rate coefficients of phosphorus-containing reactions.
Methods. Using a photochemical column model, we simulated Venus-like conditions and varied the chemical rate coefficients with a Monte Carlo (MC) approach in order to estimate the associated error in the PH3 abundances throughout the atmosphere.
Results. Current uncertainties and missing data in photochemical rate coefficients lead to a variation of about six orders of magnitude in the modelled PH3 abundance on Venus, assuming photochemical production of PH3 from tetraphosphorus hexoxide (P4O6) pathways. Our results suggest an abiotically produced upper limit of 2 ppb PH3 between 50 and 60 km. These concentrations are in the range of a recent reanalysis of Atacama Large Millimeter Array (ALMA) data, suggesting planet-averaged abundances in PH3 of 1–4 ppb above 55 km. Future observations of phosphorus monoxide (PO) on Venus would be beneficial for increasing our confidence in assessing PH3 as a biosignature.
Conclusions. We conclude that due to the large uncertainties in phosphorus chemistry, even a firm detection of several ppb PH3 in the Venus atmosphere would not necessarily mean a biological origin.
Key words: planets and satellites: atmospheres / astrobiology / astrochemistry / planets and satellites: terrestrial planets
© The Authors 2023
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://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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