Scientists Have Re-analyzed Their Data and Still See a Signal of Phosphine at Venus—Just Less of Ithttps://phys.org/news/2020-11-scientists-re-analyzed-phosphine-venusjust.htmlIn September, an international team announced that they had discovered phosphine gas (PH3) in the atmosphere of Venus based on data obtained by the Atacama Millimeter-submillimeter Array (ALMA) in Chile and the James Clerk Maxwell Telescope (JCMT) in Hawaii. The news was met with its fair share of skepticism and controversy since phosphine is considered a possible indication of life (AKA a biosignature).
Shortly thereafter, a series of papers was published that questioned the observations and conclusions, with one team going as far as to say there was "no phosphine" in Venus's atmosphere at all. Luckily, after re-analyzing the ALMA data, the team responsible for the original discovery concluded that there is indeed phosphine in the cloud tops of Venus—just not as much as they initially thought.
In the original study, which was published in the Sept. 14th issue of Nature Astronomy, the team presented findings from ALMA and the JCMT that indicated the presence of PH3 around Venus' cloud deck. On Earth, phosphine is part of the phosphorus biochemical cycle and is likely the result of phosphate reduction in decaying organic matter. On Venus, there are no known chemistry or photochemical pathways for its creation.
... In one study, which was led by researchers from NASA Goddard and appeared in a Nature Astronomy article (Oct. 26, 2020), also cast doubt on the analysis and interpretation of the ALMA and JCMT datasets. Here, the research team indicated that the spectral data that was interpreted as phosphine (PH3) was actually too close to sulfur dioxide (SO2), which is common in Venus atmosphere.
According to another study that was led by Leiden University (November 17, 2020, Astronomy & Astrophysics), the spectral data obtained by ALMA could be explained by the presence of compounds other than phosphine gas. From this, they concluded that there "no statistically significant detection of phosphine" in Venus' atmosphere and that the previous results were, in fact, "spurious."
Jane Greaves, who led the discovery team (and is an astronomer at Cardiff University, U.K.), claims that they were motivated to reexamine their original conclusions because the original ALMA data contained a "spurious signal" that could have thrown off their results. When the corrected ALMA data was posted on November 16th, Greaves and her colleagues ran a fresh analysis and posted it ahead of peer review on arXiv.
According to Greaves and her colleagues, the ALMA data demonstrated a spectral signature that cannot be explained by anything other than the compound phosphene. This, they claim, is further bolstered by the JCMT spectra that indicated the chemical fingerprints of phosphine.
Based on the new ALMA data, the team estimates that phosphine levels average at about 1 ppb—about one-seventh of their earlier estimate.
These levels, they indicate, likely peak at five parts per billion (ppm) and vary over time and depending on location. If true, this situation is similar to what scientists have observed on Mars, where methane levels wax and wane over the course of a Martian year and vary from place to place.
Inspired by the possibility, biochemist Rakesh Mogul of the California State Polytechnic University in Pomona and his colleagues reexamined data from NASA's Pioneer Venus mission. In 1978, this missions studies Venus' cloud layer using a probe that it dropped into the atmosphere. Based on their reanalysis of the data, Mogul and his colleagues found evidence of phosphorus.
This could evidence of phosphine or some other phosphorus compound, though Mogul and his team believe phosphine is the most likely candidate. Regardless, several scientists argued at VEXAG that a modest level of even 1 ppm phosphine cannot be attributed to processes like volcanism or lightning. There was also the recent announcement that the amino acid glycine was discovered in Venus's atmosphere, another potential biomarker.
Alexandra Witze.
Prospects for life on Venus fade—but aren't dead yet,
Nature (2020)
https://www.nature.com/articles/d41586-020-03258-5