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Did Pioneer see phosphine in the clouds of Venus decades ago?



The discovery of phosphine in the atmosphere of Venus has aroused much interest. It has the potential to be a biological signature, although researchers have thrown cold water on that idea since the discovery.

But it appears, at least, that the discovery is real and that one of NASA’s Pioneer spacecraft detected the elusive gas in 1978. And while it’s not necessarily a biological signature, the authors of a new study think it is necessary to rethink the chemistry of the gas. atmosphere of Venus.

The recent study found only small amounts of phosphine in Venus’s atmosphere – 20 parts per billion. But it was still there. And it appears to have been there for a while, according to the results of a new document.

A team of researchers announced Pioneer̵

7;s data on phosphine in a paper titled “Is Phosphine in the Mass Spectra from Venus’ Clouds?” The lead author is Rakesh Mogul, a professor of biological chemistry at California State Polytechnic University. Mogul is also associated with the SETI Institute and NASA’s Office of Planetary Protection. The document is available on the pre-press site arxiv.org.

“Considering the implications of phosphine (PH3) detection reported by a single spectral line by Greaves et al., We were inspired to re-examine the data obtained from the Pioneer-Venus Large Probe (LNMS) neutral mass spectrometer to look for evidence of phosphorus compounds. “the researchers write at the beginning of their paper.

The Pioneer Venus Multiprobe, also called the Pioneer Venus 2, or Pioneer 13, detected this with its Large Probe Neutral Mass Spectrometer (LNMS) instrument.

Engineers inspecting NASA's Pioneer Venus Multiprobe space bus with the four probes attached. Image Credit: from NASA Ames Research Center (NASA-ARC) - http://nix.larc.nasa.gov/info;jsessionid=6v6flfypvl37?id=AC77-0376-8&orgid=9, public domain, https: // commons .wikimedia.org / w / index.php? curid = 2354021
Engineers inspecting NASA’s Pioneer Venus Multiprobe space bus with the four probes connected. Image Credit: from NASA Ames Research Center (NASA-ARC) – http://nix.larc.nasa.gov/info;jsessionid=6v6flfypvl37?id=AC77-0376-8&orgid=9, public domain, https: // commons .wikimedia.org / w / index.php? curid = 2354021

The nomenclature around NASA’s Pioneer program deserves some clarification. There were actually two Pioneer programs.

The first involved a series of spacecraft launched between 1958 and 1960. It sent spacecraft to orbit the Moon, to fly over the Moon and to investigate the interplanetary space between Venus and Earth.

The second part launched spacecraft between 1965 and 1992. It sent four spacecraft, two of which were sent to Venus. These two included the Pioneer Venus project, consisting of the Pioneer Venus Orbiter and the Pioneer Venus Multiprobe.

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It is the Pioneer Venus Multiprobe (PVM) and the collected data that are at the heart of this study. The PVM consisted of a main spacecraft carrying four separate probes. One was large and three were smaller. On December 9, 1978, all four probes were released into the Venusian atmosphere in different locations, collecting data as they descended through the thick clouds.

A NASA poster from the archives illustrates the components of the Pioneer Venus Multiprobe. Image credit: from NASA / Glenn Research Center - https://archive.org/details/C-1978-1565, public domain, https://commons.wikimedia.org/w/index.php?curid=71788219
A NASA poster from the archives illustrates the components of the Pioneer Venus Multiprobe. Image credit: from NASA / Glenn Research Center – https://archive.org/details/C-1978-1565, public domain, https://commons.wikimedia.org/w/index.php?curid=71788219

The largest of the four probes is simply called the Large Probe. He carried more instruments than the smaller probes; seven, in fact. And he lowered himself by parachute, while the other three did not. One of his tools was the Large Probe Neutral Mass Spectrometer

When Greaves et al discovered phosphine in the upper layers of Venus ‘clouds, the team of researchers behind this work set out to look for evidence of the previous days’ phosphine. Since the LNMS studied neutral gases and their masses at different altitudes, they thought that perhaps it “saw” phosphine in the upper layers of the clouds, way back in 1978.

After reviewing the data, the team wrote: “We find that the LMNS data supports the presence of phosphine; although the origins of the phosphine remain unknown. “

The Pioneer Venus Multiprobe released a total of four probes into the Venusian atmosphere. Image credit: from NASA - http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19780020162.pdf, public domain, https://commons.wikimedia.org/w/index.php ? curid = 38737173
The Pioneer Venus Multiprobe released a total of four probes into the Venusian atmosphere. Image credit: from NASA – http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19780020162.pdf, public domain, https://commons.wikimedia.org/w/index.php ? curid = 38737173

It took some work to come to that conclusion. After all, the data is over 40 years old.

They start by testing the accuracy of the data and the tool that collected it, to be sure. “To estimate the resolution and resolving power of the LNMS, we first compared the measured and expected masses for CO2, SO2, N2, 40Ar and 36Ar, identified by Hoffman et al,” they write. “In all cases, the measured masses (from the spectra) and the expected masses differed by <0.003 amu ). “This difference is not significant in this work. In their article, they explain the accuracy of their data in more detail.

“With this in mind, we used high resolution data and dynamic range to discover the presence of phosphine. We note that phosphorus compounds were not reported in the initial analyzes… ”of the LNMS data. But this does not mean that the signal was not present.

The authors say that the data confirm the presence of phosphine in the atmosphere of Venus. They also list some other conclusions, which only those with a particularly chemical mind might find interesting. Interested readers can check out the document, which is a fairly short read.

In short, there is some initial ambiguity in the readings, suggesting that what appears to be PH3 could potentially be H.2S, or hydrogen sulfide. But in the end it is PH3 and his brother PH2 this explains it, in the authors’ analysis.

Venus balloon missions have been proposed for both exploration and colonization. Image credit: NASA
Venus balloon missions have been proposed for both exploration and colonization. Image credit: NASA

They also found other inconsistent data for other chemicals in Venus’s atmosphere. Again, this might only be of interest to the chemically minded people among us, but it’s worth mentioning. They say the presence of these chemicals is in contrast to the oxidizing atmosphere of Venus. These include methane, nitrous oxide, and hydrogen peroxide.

In their conclusion, the authors write that “this reassessment of the mass spectra of Venus shows the revelation of atomic phosphorus as a fragmentation product from a neutral gas. Furthermore, the spectra show a tantalizing possibility for the presence of PH3, along with its fragments. Associates … “

They also point out that the LNMS signal for phosphine is weak, but it matches the figure of 20 ppb in the study a couple of weeks ago.

“Although the peak intensities are low, perhaps they are consistent with
the abundances of ~ 20 ppb reported by Greaves et al. Together, the assignment attempts suggest that the reported abundances of H2S (from mass spectra) in Venus’ atmosphere may indeed be PH3; “

This figure from the study shows the tentative assignments of different chemicals to the spectra obtained by the Neutral Mass Spectrometer on NASA's Venus Pioneer spacecraft. Image credit: Mogul et al, 2020.
This figure from the study shows the tentative assignments of different chemicals to the spectra obtained by the neutral mass spectrometer on NASA’s Venus Pioneer spacecraft. Image credit: Mogul et al, 2020.

In total, the team thinks we may need to rethink Venus’s atmosphere and its potential to host life. Not just because of the Greaves et al study, but because of their own results. “We believe this is an indication of undiscovered and / or potentially life-enhancing chemicals.”

“Looking ahead,” they write, “and to better understand the potential for imbalances in the clouds, we need a sustained approach to the exploration of Venus.”

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