Constraints on the Production of Phosphine by Venusian Volcanoes
, Sukrit Ranjan 5,6,7, Paul B. Rimmer 3,8, Janusz J. Petkowski 1, Jane S. Greaves 2 and Sara Seager 1,9,10
Johan Varekamp
Round 1
Reviewer 1 Report
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Author Response
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Reviewer 2 Report
The authors of the manuscript study the possibility of abiotic origin of PH3 in the clouds of Venus atmosphere,.-due to volcanic eruptions. Phosphine is known as a biomarker in the Earth atmosphere so its detection is of great interest..
On the basis of hypothesis considering a mantle plume volcanism as a source of the PH3, tentatively detected on Venus, a quantitative model was constructed in terms of atmospheric chemistry, mantle chemistry, and the eruption physics and chemistry. In 2020 , there was a sensational report by Greaves et al about the detection of ~20 ± 10 ppb (5-7 ppb after recalibration) phosphine from the absorption line near 1 mm in the low clouds of Venus, below 60 km. Line of phosphine is overlapped by the SO2 line which presents in the atmosphere, so the value of tentative detected abundance of phosphine may be overestimated. SOIR/VEX gave a much lower upper limit < 0.5 ppb above 60 km. Baines et al concluded that to be detected a reasonable PH3 abundance in Venus clouds may be at least 1 ppb.
It was found by the authors from the model calculations that the minimum rate of eruption needed to produce 1ppb phosphine in the clouds should provide ≥21,600 km3 /year of magma erupted. It is a strong constrain on vollcano eruption source of phosphine: indeed, if a tentatively found 1ppb PH3 in the clouds is real the most likely scenario would suggest Venus to be entering a global resurfacing epoch, such as that proposed to have occurred ~300Mya. It is strong constrain for possible volcanic source of phosphine in Venus atmosphere. If phosphine is really, not tentatively, found in Venus atmosphere, it would mean that the gigantic eruption happens on Venus at a current time. Otherwise, phosphine most probably has a biogenic origin.
The manuscript may be recommended for publishing.
Author Response
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