In 2020 a spectroscopic analysis of the atmosphere of Venus was reported by Jane Greaves. She and her team had made observations in 2017 using the James Clerk Maxwell submillimetre-wavelength radio telescope at Mauna Kea Observatory in Hawaii. These observations showed signs of phosphine in the atmosphere of Venus in quantities that could not be explained by known abiotic processes. Later re-analysis of this work showed interpolation errors had been made, and re-analysis of data with the fixed algorithm do not result in the detection of phosphine. A similar negative finding of phosphine was made on three flights in November 2021 using the SOFIA far-infrared telescope which is carried for high altitude observations in a Boeing 747. The authors of the original study then claimed to still detect it with a much lower concentration of 1 ppb.
Phosphine is a colorless, flammable, highly toxic compound with the chemical formula PH3, classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting fish, due to the presence of substituted phosphine and diphosphane (P2H4). On Earth, where there is almost no loose hydrogen, phosphine is generated by microorganisms living in an anaerobic environment or by industrial processes; this does not rule out novel abiotic sources in the extreme Venutian environment.
With extreme surface temperatures reaching nearly 735 K and an atmospheric pressure 92 times that of Earth, the conditions on Venus make water-based life as we know it unlikely on the surface of the planet. However, a few scientists have speculated that thermoacidophilic extremophile microorganisms might exist in the temperate, acidic upper layers of the Venusian atmosphere. In June 2021, calculations of water activity levels in Venusian clouds based on data from space probes showed these to be two magnitudes too low at the examined places for any known extremophile bacteria to survive.
In 2023 Greaves, speaking at Royal Astronomical Society's National Astronomy Meeting in Cardiff, Wales; released new findings. Again using the Maxwell Radio-Telescope, her team discovered phosphine spectral lines deeper in the atmosphere of Venus than in the previous observations.
NASA has two probes scheduled for Venus in the early 2030s, VERITAS an orbiter with packages to do spectral atmospheric chemistry analysis, as well as the DIVINCI probe (Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging); which will include an atmospheric descent probe able to directly sample and analyze atmospheric gas chemistry.
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