Life on Venus
Studies continue to question whether life could have existed on the planet's surface before a runaway greenhouse effect took hold, and whether a relict biosphere could persist high in the modern Venusian atmosphere.
[7][8] As of 8 February 2021, an updated status of studies considering the possible detection of lifeforms on Venus (via phosphine) and Mars (via methane) was reported, though whether these gases are present is still unclear.
[10] Because Venus is completely covered in clouds, human knowledge of surface conditions was largely speculative until the space probe era.
"[14] Since then, increasingly clear evidence from various space probes showed Venus has an extreme climate, with a greenhouse effect generating a constant temperature of about 500 °C (932 °F) on the surface.
[26][27] However, the resurfacing of the planet in the past 500 million years[28] means that it is unlikely that ancient surface rocks remain, especially those containing the mineral tremolite which, theoretically, could have encased some biosignatures.
[32] Between 700 and 750 million years ago, a near-global resurfacing event triggered the release of carbon dioxide from rock on the planet, which transformed its climate.
[33] In addition, according to a study from researchers at the University of California, Riverside, Venus would be able to support life if Jupiter had not altered its orbit around the Sun.
[50][51][52] In 2021, it was suggested the color of "unknown UV absorber" match that of "red oil", a known substance comprising a mix of organic carbon compounds dissolved in concentrated sulfuric acid.
[53] Research published in September 2020 indicated the detection of phosphine (PH3) in Venus's atmosphere by Atacama Large Millimeter Array (ALMA) telescope that was not linked to any known abiotic method of production present or possible under Venusian conditions.
[54][55][56][57] A molecule like phosphine is not expected to persist in the Venusian atmosphere since, under the ultraviolet radiation, it will eventually react with water and carbon dioxide.
[58] Related studies suggested that the initially claimed concentration of phosphine (20 ppb) in the clouds of Venus indicated a "plausible amount of life," and further, that the typical predicted biomass densities were "several orders of magnitude lower than the average biomass density of Earth’s aerial biosphere.”[59][60] As of 2019[update], no known abiotic process generates phosphine gas on terrestrial planets (as opposed to gas giants[61]) in appreciable quantities.
[65] In a statement published on October 5, 2020, on the website of the International Astronomical Union's commission F3 on astrobiology, the authors of the September 2020 paper about phosphine were accused of unethical behaviour and criticized for being unscientific and misleading the public.
They also respond to points raised in a critical study by Villanueva et al. that challenged their conclusions and find that so far the presence of no other compound can explain the data.
Johannes Benkhoff, project scientist, believed BepiColombo's MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) could possibly detect phosphine, but "we do not know if our instrument is sensitive enough".
[76] In 2022, observations of Venus using the SOFIA airborne infrared telescope failed to detect phosphine, with an upper limit on the concentration of 0.8 ppb announced for Venusian altitudes 75–110 km.
[57] A subsequent reanalysis of the SOFIA data using nonstandard calibration techniques resulted in a phosphine detection at the concentration level ~ 1 ppb,[77] but this work is yet to be peer-reviewed and therefore remains questionable.
[78] ALMA restarted 17 March 2021 after a year-long shutdown in response to the COVID-19 pandemic and may enable further observations that could provide insights for the ongoing investigation.
The Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy mission (VERITAS) would carry radar to view through the clouds to get new images of the surface, of much higher quality than those last photographed thirty-one years ago.
[83] According to new research announced in January 2021, the spectral line at 266.94 GHz attributed to phosphine in the clouds of Venus was more likely to have been produced by sulfur dioxide in the mesosphere.
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.
Instead, it was proposed that Venusian "life" may be based on self-replicating molecular components of "red oil" – a known class of substances consisting of a mixture of polycyclic carbon compounds dissolved in concentrated sulfuric acid.
