Context: ALMA observations of Venus at 267 GHz have been presented in the
literature that show the apparent presence of phosphine (PH3) in its
atmosphere. Phosphine has currently no evident production routes on the
planet's surface or in its atmosphere.
Aims: The aim of this work is to assess the statistical reliability of the
line detection by independent re-analysis of the ALMA data.
Methods: The ALMA data were reduced as in the published study, following the
provided scripts. First the spectral analysis presented in the study was
reproduced and assessed. Subsequently, the spectrum was statistically
evaluated, including its dependence on selected ALMA baselines.
Results: We find that the 12th-order polynomial fit to the spectral passband
utilised in the published study leads to spurious results. Following their
recipe, five other >10 sigma lines can be produced in absorption or emission
within 60 km/s from the PH3 1-0 transition frequency by suppressing the
surrounding noise. Our independent analysis shows a feature near the PH3
frequency at a ~2 sigma level, below the common threshold for statistical
significance. Since the spectral data have a non-Gaussian distribution, we
consider a feature at such level as statistically unreliable that cannot be
linked to a false positive probability.
Conclusions: We find that the published 267-GHz ALMA data provide no
statistical evidence for phosphine in the atmosphere of Venus.
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