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Venus Life Prospects

Phosphine biomarker molecule
Phosphine biomarker molecule
Phosphine biomarker molecule

Phosphine Basic Facts

Composed of 1 phosphorus atom and 3 hydrogen atoms (PH³)

Phosphine on Earth is exclusively associated with anaerobic (O2-free) life or human industry

Phosphine Detection Basic Facts

Amount detected (ppb)

A few ppb

Where phosphine is detected (km)

>53-61  km altitude

Life-time of phosphine in the clouds

A few hours in the lower parts of the atmosphere compared to centuries in the >60-80 km layer.

Observations Facts

Telescopes

James Clerk Maxwell Telescope (RxA instrument)

 

ALMA, the Atacama Large Millimeter/submillimeter Array (Band 3)

Observation dates

June 2017 (JCMT)
March 2019 (ALMA)

Frequency of observations

266.9664 GHz (a wavelength of 1.123 mm)

Concentrated Sulfuric Acid and Biomolecules

Venus’ clouds permanently cover the entire planet, are extensive vertically, and the cloud layers have the right temperature for life. Because Earth’s clouds host bacteria, the overall picture may at first seem promising for microbial-type life in the Venus clouds. The Venus clouds are not made of life-friendly water but of concentrated sulfuric acid. Because concentrated sulfuric acid is deadly to Earth’s life, many cannot entertain the idea of life in the Venusian clouds. Yet, we have found a growing number of biomolecules that are stable in concentrated sulfuric acid. While a large majority of biomolecules are unstable in sulfuric acid, our exploration is just the beginning of research that may suggest a rich and diverse organic chemistry in the Venusian clouds.

Amino Acids: Our twenty biogenic amino acids, with one exception, are stable in concentrated sulfuric acid. About half are unchanged over the months we have monitored them. The other half are stable after they are chemically modified by the concentrated sulfuric acid (sulfonated or sulfated). Seager et al. 2024

 

Nucleic Acid Bases: Our nucleic acid bases and their chemical cores purine and pyrimidine are stable in concentrated sulfuric acid for over the 18 months we have monitored them. These molecules are protonated by the sulfuric acid. M.Seager et al. 2023.

Front cover of Astrobiology magazine showing Venus

Amphiphilic Lipids: The lipids are not only stable in concentrated sulfuric acid but point their polar heads outward in concentrated sulfuric acid forming tiny spherical vesicles the size of cells. Duzedevich et al., submitted 2024.

Illustration showing fluorescent microspectroscopy

Fluorescence microscopy image of lipid vesicles in 80% v/v sulfuric acid.

Production of Organic Molecules: “New experiments show rich organic chemistry in concentrated sulfuric acid with simple organic molecules or even atmospheric gases (e.g. formaldehyde and CO gas) as starting points. Photochemistry, meteoritic delivery or lightning could contribute the precursors for complex organics in the Venus clouds. Spacek et al. 2023

Illustration showing Proposed organic carbon cycle in the atmosphere of Venus

Proposed organic carbon cycle in the atmosphere of Venus. Complex organic molecules can form in concentrated sulfuric acid droplets from simple precursor molecules.

Microbial Life in Venus’ Clouds

Any microbial life that might exist in Venus’ atmosphere will be so different than any Earth life in terms of its composition, because of the extreme conditions in the Venus atmosphere. Conditions in Venus’ habitable atmosphere layer are fifty times drier than the driest place on Earth (the Atacama Desert) and billions of times more acidic than the most acidic environment on Earth (Ethiopia’s Dallol pools).

Illustration of Microbial Life in Venus’ Clouds

A Proposed Venus Life Cycle

A key question for life on Venus is how can microbial-type life persist aloft in the atmosphere for hundreds of millions to billions of years? Most discussions of life on Venus never address whether the life is free floating in the atmosphere or alternatively confined to the liquid environment inside cloud droplets. We argue life must reside inside liquid droplets, so that it will be protected from a fatal net loss of liquid to the atmosphere, an unavoidable problem for any free-floating microbial life forms. Yet, the droplet habitat poses a lifetime limitation: droplets inexorably grow (over a few months) to large enough sizes that are forced by gravity to settle downwards to hotter, uninhabitable layers of the Venusian atmosphere. We propose for the first time that the only way life can survive indefinitely is with a life cycle that involves microbial life drying out as liquid droplets evaporate during settling, with the small desiccated “spores” halting at and partially populating the Venus atmosphere stagnant lower haze layer (33-48 km altitude). We thus call the Venusian lower haze layer a “depot” for desiccated microbial life. The spores eventually return to the cloud layer by upward diffusion caused by mixing induced by gravity waves, act as cloud condensation nuclei, and rehydrate for a continued life cycle. For more information see this journal article (Seager et al. 2021).

Diagram showing habitable layer of the atmosphere

Atmosphere layers of Venus depicting the “habitable” layer of the atmosphere and a hypothesized lifecycle of microbial life that could persist in the atmosphere. Figure credit: Johanna Petkowska.

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