In the absence of direct observations of extraterrestrial life, scientists often focus on searching for biosignatures, chemical by-products of life, that can be detected with remote sensing. Although Mars has received the most attention in this regard, other solar system worlds with atmospheres also have been investigated.
In 2021, planetary astronomers reported a detection of phosphine gas in the atmosphere of Venus using ground-based radio observations. The concentration of the gas was initially reported to be 20 parts per billion but was later revised to seven or fewer parts per billion on the basis of improved calibration and analysis of the data. On Earth, phosphine can be associated with biological processes, and researchers are studying whether the gas may be used as a sign of life on other planets.
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