Venus’s extreme greenhouse effect pushes surface temperatures to 460 °C—hot enough to melt lead. But the planet’s dense clouds, located at an altitude of about 50–70 km, are a balmy 20 °C. In 2020 Cardiff University’s Jane Greaves and colleagues presented the first evidence for the presence of phosphine (PH3) gas in Venus’s upper atmosphere. Phosphine has been discussed as a potential biomarker for the presence of life on planets, and the putative discovery led to a reappraisal of the possible sources and sinks of atmospheric phosphorus-bearing gases.
The evidence presented by Greaves and colleagues was based on two measurements—a tentative detection of the molecule’s spectral line using the James Clerk Maxwell Telescope (JCMT) in Hawaii and a more convincing detection of the same line using Chile’s Atacama Large Millimeter/Submillimeter Array (ALMA). Armed with those data, the researchers interpreted the abundance at 20 parts per billion; a later recalibration of the data suggested a range of 1–7 ppb. But three subsequent investigations found no significant evidence for PH3 absorption in the same JCMT and ALMA data.
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