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Thread: Phosphine, a strong biosignature, has been detected in the atmosphere of Venus

  1. #61
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    Perhaps it's worth contextualising the reported phosphine by looking at whether other simple hydrogen compounds, such as methane (CH4), ammonia (NH3) and hydrogen sulfide (H2S) have been detected in the atmosphere of Venus...

    It turns out that space probe data has given apparent indications of all these compounds. Venera 8 (1972) found indications of NH3. Pioneer Venus Large Probe (1978) found indications of NH3 and H2S.

    These are the papers I found

    Ammonia in the atmosphere of Venus

    Venus methane and water

    Composition of the atmosphere of Venus below the clouds


    The apparent indications of NH3 and CH4 were treated with scepticism by scientists. But considering how little research has been done on Venus in the last few decades, can probe data from the seventies be disregarded?

    If all these simple hydrogenated molecules are there, how does it relate to the phosphine finding?

    Methane, ammonia and hydrogen sulfide, like phosphine, are produced on Earth by micro-organisms in conditions which are anoxic (lacking O2 molecules) yet comparatively oxidising (rich in oxygen compounds). The microbial chemistry breaks bonds between oxygen and another element (carbon, nitrogen, sulfur, or phosphorus), and bonds the C, N, S, or P with hydrogen instead. This makes oxygen atoms available for energy-producing reactions (anaerobic respiration).

    So the apparent presence of CH4, NH3, and H2S is consistent with the hypothesis that the apparent presence of PH3 is due to life. But doesn't necessarily rule out geothermal activity either, as this can produce a range of hydrogen-rich molecules.

    Another reason methane (CH4) is interesting... Compared to other simple carbon compounds, such as CO2, CH4 is chemically more similar to biomolecules, which typically contain large numbers of carbon-hydrogen bonds (as well as carbon-carbon bonds).
    Last edited by Colin Robinson; 2020-Oct-01 at 08:11 PM.

  2. #62
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    Quote Originally Posted by Colin Robinson View Post
    Perhaps it's worth contextualising the reported phosphine by looking at whether other simple hydrogen compounds, such as methane (CH4), ammonia (NH3) and hydrogen sulfide (H2S) have been detected in the atmosphere of Venus...

    It turns out that space probe data has given apparent indications of all these compounds. Venera 8 (1972) found indications of NH3. Pioneer Venus Large Probe (1978) found indications of NH3 and H2S.
    I meant to write: Pioneer Venus Large Probe (1978) found indications of CH4 and H2S.

  3. #63
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    In the meantime, controversy has been unfolding over the 'apparent discovery' announcement:

    The IAU (International Astronomy Union) have taken the discovery team to task, with the IAU having ancountered attacks from multiple sources, as well as the discovery itself being very much in question:
    Controversy erupts among astronomers over whether phosphine really was discovered on Venus – Physics World

    Synopsis is (my words): Possible parasitic effects ensuing from Greaves etal using a 12 order polynomial to remove the background continuum of thermal emission from Venus spectrum, (albeit for good reasons, ie: removal of 'instrumental artefacts'). This same refutation has been presented by two independent teams, now.

    What is evident, is that this is yet another classic example of peer review doing its job.

    The matter seems destined to reach a solid conclusion (ie: on the validity of the original announcement), with there being a way to resolve it using high altitude (airborne) observational measurements. (Which would be good news).

    Definitely one worthy of keeping an eye on for further updates ..

  4. #64
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    Two reports out in mid-November within a day of each other.

    --------

    https://arxiv.org/abs/2011.08176

    Re-analysis of Phosphine in Venus' Clouds

    Jane S. Greaves, Anita M. S. Richards, William Bains, Paul B. Rimmer, David L. Clements, Sara Seager, Janusz J. Petkowski, Clara Sousa-Silva, Sukrit Ranjan, Helen J. Fraser

    We first respond to two points raised by Villanueva et al. We show the JCMT discovery spectrum of PH3 can not be re-attributed to SO2, as the line width is larger than observed for SO2 features, and the required abundance would be an extreme outlier. The JCMT spectrum is also consistent with our simple model, constant PH3-abundance with altitude, with no discrepancy in line profile (within data limits); reconciliation with a full photochemical model is the subject of future work. Section 2 presents initial results from re-processed ALMA data. Villanueva et al. noted an issue with bandpass calibration. They have worked on a partially re-processed subset of the ALMA data, so we note where their conclusions, and those of Greaves et al., are now superseded. To summarise: we tentatively recover PH3 in Venus' atmosphere with ALMA (~5{\sigma} confidence). Localised abundance appears to peak at ~5 parts-per-billion, with suggestions of spatial variation. Advanced data-products suggest a planet-averaged PH3 abundance ~1 ppb, ~7 times lower than from the earlier ALMA processing. The ALMA data are reconcilable with the JCMT detection (~20 ppb) if there is order-of-magnitude temporal variation; more advanced processing of the JCMT data is underway to check methods. Independent PH3 measurements suggest possible altitude dependence (under ~5 ppb at 60+ km, up to ~100 ppb at 50+ km; see Section 2: Conclusions.) Given that both ALMA and JCMT were working at the limit of observatory capabilities, new spectra should be obtained. The ALMA data in-hand are no longer limited by calibration, but spectral ripples still exist, probably due to size and brightness of Venus in relation to the primary beam. Further, spatial ripples are present, potentially reducing significance of real narrow spectral features.

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    https://arxiv.org/abs/2010.15188

    The statistical reliability of 267 GHz JCMT observations of Venus: No significant evidence for phosphine absorption

    M.A. Thompson

    In the light of the recent announcement of the discovery of the potential biosignature phosphine in the atmosphere of Venus I present an independent reanalysis of the original JCMT data to assess the statistical reliability of the detection. Two line detection methods are explored, low order polynomial fits and higher order multiple polynomial fits. A non-parametric bootstrap analysis reveals that neither line detection method is able to recover a statistically significant detection. Similar to the results of other reanalyses of ALMA Venus spectra, the polynomial fitting process results in false positive detections in the JCMT spectrum. There is thus no significant evidence for phosphine absorption in the JCMT Venus spectra.
    Do good work. —Virgil Ivan "Gus" Grissom

  5. #65
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    Would life on Venus be derived from life on Earth? Panspermia by asteroids once again raises its head.


    https://arxiv.org/abs/2009.09512

    Transfer of Life Between Earth and Venus with Planet-Grazing Asteroids

    Amir Siraj, Abraham Loeb

    Recently, phosphine was discovered in the atmosphere of Venus as a potential biosignature. This raises the question: if Venusian life exists, could it be related to terrestrial life? Based on the known rate of meteoroid impacts on Earth, we show that at least ∼6 × 10^5 asteroids have grazed Earth's atmosphere without being significantly heated and later impacted Venus, and a similar number have grazed Venus's atmosphere and later impacted the Earth, both within a period of ∼10^5 years during which microbes could survive in space. Although the abundance of terrestrial life in the upper atmosphere is unknown, these planet-grazing shepherds could have potentially been capable of transferring microbial life between the atmospheres of Earth and Venus. As a result, the origin of possible Venusian life may be fundamentally indistinguishable from that of terrestrial life.
    Do good work. —Virgil Ivan "Gus" Grissom

  6. #66
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    Two more papers closely related to the phosphine announcement. The second paper was written by some of the "phosphine discovery" team members.


    https://arxiv.org/abs/2009.07835

    On The Biomass Required To Produce Phosphine Detected In The Cloud Decks Of Venus

    Manasvi Lingam, Abraham Loeb

    The detection of phosphine in the atmosphere of Venus at an abundance of ∼20 ppb suggests that this gas is being generated by either indeterminate abiotic pathways or biological processes. We consider the latter possibility, and explore whether the amount of biomass required to produce the observed flux of phosphine may be reasonable. We estimate that the typical biomass densities predicted by our simple model are potentially orders of magnitude lower than the biomass density of Earth's aerial biosphere in the lower atmosphere. We briefly discuss how small spacecraft could sample the Venusian cloud decks and search for biomarkers.

    =====

    https://arxiv.org/abs/2009.06474

    The Venusian Lower Atmosphere Haze as a Depot for Desiccated Microbial Life: A Proposed Life Cycle for Persistence of the Venusian Aerial Biosphere

    Sara Seager, Janusz J. Petkowski, Peter Gao, William Bains, Noelle C. Bryan, Sukrit Ranjan, Jane Greaves

    We revisit the hypothesis that there is life in the Venusian clouds to propose a life cycle that resolves the conundrum of how life can persist aloft for hundreds of millions to billions of years. Most discussions of an aerial biosphere in the Venus atmosphere temperate layers never address whether the life-small microbial-type particles-is free floating or confined to the liquid environment inside cloud droplets. We argue that life must reside inside liquid droplets such 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. However, 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 downward to hotter, uninhabitable layers of the Venusian atmosphere. (Droplet fragmentation-which would reduce particle size-does not occur in Venusian atmosphere conditions.) 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. We also review the challenges for life in the extremely harsh conditions of the Venusian atmosphere, refuting the notion that the 'habitable' cloud layer has an analogy in any terrestrial environment.
    Do good work. —Virgil Ivan "Gus" Grissom

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