Publications

Life on Venus

Building on the work of Rimmer et al. 2021, the model predicts that the clouds are not entirely made of sulfuric acid, but partially composed of ammonium salt slurries, which may be the result of biological production of ammonia in cloud droplets. As a result, the clouds are no more acidic than some extreme terrestrial environments that harbor life. Life could be making its own environment on Venus.

The model’s predictions for the abundance of gases in Venus’ atmosphere matches observation better than any previous model, and reconcile decades-long atmosphere anomalies.
Bains, W., Petkowski, J. J., Rimmer, P. B., & Seager, S. (2021). Production of Ammonia Makes Venusian Clouds Habitable and Explains Observed Cloud-Level Chemical AnomaliesProceedings of the National Academy of Sciences, 00(00), 00-00. Embargoed until publication.

The mysterious UV absorber in the top clouds of Venus has defied explanation for close to a century.

A new study proposes that the UV absorber involves organic molecules inside the Venus cloud particles. Simple organic molecules can be formed from seed carbon compounds undergoing a chain of chemical reactions that lead to a rich variety of organic molecules. UV radiation is relevant for some reactions. The simple organic molecules originate from meteoritic delivery, photochemistry, or even possibly life itself.
Spacek, J. (2021). Organic Carbon Cycle in the Atmosphere of VenusarXiv preprint arXiv:2108.02286.

The clouds of Venus might not be as inhospitable as previously thought.

Alternative interpretations to in situ measurements yield potentially habitable conditions with water activities (0.585) and buffered acidities pH ~0 that lie within the limits of terrestrial microbial growth.
Mogul, R., Limaye, S. S., Lee, Y. J., & Pasillas, M. (2021). Potential for phototrophy in Venus’ cloudsAstrobiology21(10), 1237-1249.

A new model of the chemistry of the atmosphere of Venus suggests that the clouds are not entirely made of sulfuric acid, but of salts.

The model predicts that the acidity of some cloud particles is much higher than previously thought and could reach the pH of around 1.
Rimmer, P. B., Jordan, S., Constantinou, T., Woitke, P., Shorttle, O., Hobbs, R., & Paschodimas, A. (2021). Hydroxide salts in the clouds of Venus: their effect on the sulfur cycle and cloud droplet pHThe Planetary Science Journal2(4), 133.

People wonder if water is be the only possible solvent for life. If life on Venus exist then it can use concentrated sulfuric acid as a solvent rather than water.

Our theoretical study suggest that concentrated sulfuric acid can in principle support a rich and diverse organic chemistry. However, if sulfuric acid-based life exists then it has to be completely different than Earth-like, water-based life.
Bains, W., Petkowski, J. J., Zhan, Z., & Seager, S. (2021). Evaluating Alternatives to Water as Solvents for Life: The Example of Sulfuric AcidLife11(5), 400.

We have created a database of sulfuric acid reactivity of organic chemicals as a tool to study the possibility of life in concentrated sulfuric acid solvent.

Bains, W., Petkowski, J. J., & Seager, S. (2021). A Data Resource for Sulfuric Acid Reactivity of Organic ChemicalsData6(3), 24.

Our hypothesized life cycle for the hypothetical microbial life in the Venusian atmosphere.

The paper includes a detailed description of  the extreme challenges to life of any kind in the Venusian atmosphere.
Seager, S., Petkowski, J. J., Gao, P., Bains, W., Bryan, N. C., Ranjan, S., & Greaves, J. (2021).
The Venusian Lower Atmosphere Haze as a Depot for Desiccated Microbial Life: A Proposed Life Cycle for Persistence of the Venusian Aerial Biosphere. Astrobiology21(10), 1206-1223.

Phosphine

A short summary paper on the Venusian PH3 discovery and the scientific debate that arose since the original candidate detection in September 2020.

Bains, W., Petkowski, J. J., Seager, S., Ranjan, S., Sousa-Silva, C., Rimmer, P. B., … & Richards, A. M. (2021). Venusian phosphine: a ‘Wow!’ signal in chemistry?Phosphorus Sulfur and Silicon and the Related Elements00(00), 00-00.

The announcement of the potential presence of PH3 on Venus resulted in the community showing a small but significant increase in the notion that life in the clouds of Venus is a possibility. Nevertheless, the community still considers Venus to be the least likely abode of life ranking far behind Europa, Enceladus, Mars and even behind Titan.

Bains, W. & Petkowski, J. (2021). Astrobiologists are rational but not BayesianInternational Journal of Astrobiology,20(4), 312-318.

Several authors suggested that the signal from JCMT telescope can be attributed to mesospheric SO2 instead of PH3. It is however unlikely that the contested absorption line comes from the SO2; simultaneous observation of other SO2absorptions show that the potential SO2 line-contamination is less than <10% of the observed signal.

Greaves, J. S., Rimmer, P. B., Richards, A., Petkowski, J. J., Bains, W., Ranjan, S., … & Fraser, H. J. (2021). Low Levels of Sulphur Dioxide Contamination of Phosphine Spectra from Venus’ AtmospherearXiv preprint arXiv:2108.08393.

A response to papers by Snellen et al. 2020, Villanueva et al. 2021 and Thompson 2021 that question the data processing and data interpretation of the original Venusian PH3 discovery paper. The paper shows the recovery of the PH3 in the atmosphere of Venus in data taken with ALMA, using three different calibration methods and confirms that the JCMT detection of PH3 remains robust.

Greaves, J. S., Richards, A. M., Bains, W., Rimmer, P. B., Clements, D. L., Seager, S., … & Fraser, H. J. (2021). Reply to: No evidence of phosphine in the atmosphere of Venus from independent analysesNature Astronomy5(7), 636-639.

A response to papers by Snellen et al. 2020, Villanueva et al. 2021, and Thompson 2021 that question the data processing and data interpretation of the original Venusian PH3 discovery paper. The response demonstrates that PH3-identification was not a post-hoc rationalization of a feature found after complex data processing.

Greaves, J. S., Richards, A. M., Bains, W., Rimmer, P. B., Sagawa, H., Clements, D. L., … & Hoge, J. (2021). Addendum: Phosphine gas in the cloud deck of VenusNature Astronomy5(7), 726-728.

Re-analyzed data from the Pioneer Venus Large Probe Neutral Gas Mass Spectrometer (LNMS) reveal the presence of several trace chemical species in Venus’ clouds including phosphine, hydrogen sulfide, nitrous acid (nitrite), nitric acid (nitrate), hydrogen cyanide, and possibly ammonia.

Mogul, R., Limaye, S. S., Way, M. J., & Cordova, J. A. (2021). Venus’ mass spectra show signs of disequilibria in the middle cloudsGeophysical Research Letters48(7), e2020GL091327.

Discovery paper of PH3 in the Venusian atmosphere and its implications for the presence of life.

Greaves, J. S., Richards, A., Bains, W., Rimmer, P. B., Sagawa, H., Clements, D. L., … & Hoge, J. (2021). Phosphine gas in the cloud decks of VenusNature Astronomy5(7), 655-664.

A supplementary paper to the PH3 on Venus discovery paper. Here we expand on the arguments that no known atmospheric, surface, or subsurface chemistry can explain the presence of atmospheric ppb by volume levels of PH3. The paper also discusses the volcanic sources of PH3 proposed by Truong and Lunine 2021 and other PH3 formation pathways postulated by Omran et al 2021.

Bains, W., Petkowski, J. J., Seager, S., Ranjan, S., Sousa-Silva, C., Rimmer, P. B., … & Richards, A. M. (2021). Phosphine on Venus cannot be explained by conventional processesAstrobiology21(10), 1277-1304.

We present a new model for the biological production of phosphine (PH3) in specific anaerobic environments, where the combined action of phosphate reducing and phosphite disproportionating bacteria can produce phosphine.

Bains, W., Petkowski, J. J., Sousa-Silva, C., & Seager, S. (2019).
New Environmental Model for Thermodynamic Ecology of Biological Phosphine Production. Science of The Total Environment, 658, 521-536.

Many scientists are not aware or do not believe phosphine is produced by life. In this paper we list and then dispel the four main arguments against (too toxic, no direct evidence of production from a specific species, too energetically costly to produce, unstable in O2-rich environment). We postulate that anaerobic life persisting in anoxic (O2-free) environments may exploit trivalent phosphorus chemistry much more extensively, in contrast to O2-dependent life for which phosphine is highly toxic.

Bains, W., Petkowski, J. J., Sousa-Silva, C., & Seager, S. (2019).
Trivalent Phosphorus and Phosphines as Components of Biochemistry in Anoxic Environments.Astrobiology, 19(7), 885-902.

We make the case for PH3 as a biosignature gas on exoplanets. The main conclusion is massive amounts of PH3 need to be produced by life on an exoplanet in order to generate enough PH3 to accumulate in the atmosphere for hypothetical remote sensing detection.

Sousa-Silva, C., Seager, S., Ranjan, S., Petkowski, J. J., Zhan, Z., Hu, R., & Bains, W. (2020).
Phosphine as a Biosignature Gas in Exoplanet Atmospheres. Astrobiology, 20(2), 235-268.

Phosphine Discovery in the Venusian Atmosphere

On September 14, 2020 Dr. Jane Greaves of Cardiff University announced that she detected phosphine in Venus’ atmosphere using the James Clerk Maxwell Telescope (JCMT) in Hawaii, and the Atacama Large Millimeter Array (ALMA) observatory in Chile.

The MIT team, led by Prof. Sara Seager, Dr. Janusz Petkowski, and Dr. Willliam Bains followed up the new observation with an exhaustive analysis of all known processes, other than life, that could have produced phosphine in Venus’ harsh, sulfuric environment. Based on the many scenarios they considered, the team concluded that there is no explanation for the phosphine detected in Venus’ clouds, other than the presence of life or chemical processes that are not yet known to occur on rocky planets.

MIT Initiative press release will follow when it is available (Sept. 14).

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