46 research outputs found
Venus' Atmospheric Chemistry and Cloud Characteristics Are Compatible with Venusian Life
Venus is Earth's sister planet, with similar mass and density but an
uninhabitably hot surface, an atmosphere with a water activity 50-100 times
lower than anywhere on Earths' surface, and clouds believed to be made of
concentrated sulfuric acid. These features have been taken to imply that the
chances of finding life on Venus are vanishingly small, with several authors
describing Venus' clouds as "uninhabitable", and that apparent signs of life
there must therefore be abiotic, or artefactual. In this article, we argue that
although many features of Venus can rule out the possibility that Earth life
could live there, none rule out the possibility of all life based on what we
know of the physical principle of life on Earth. Specifically, there is
abundant energy, the energy requirements for retaining water and capturing
hydrogen atoms to build biomass are not excessive, defenses against sulfuric
acid are conceivable and have terrestrial precedent, and the speculative
possibility that life uses concentrated sulfuric acid as a solvent instead of
water remains. Metals are likely to be available in limited supply, and the
radiation environment is benign. The clouds can support a biomass that could
readily be detectable by future astrobiology-focused space missions from its
impact on the atmosphere. Although we consider the prospects for finding life
on Venus to be speculative, they are not absent. The scientific reward from
finding life in such an un-Earthlike environment justifies considering how
observations and missions should be designed to be capable of detecting life if
it is there.Comment: Published in Astrobiology, June 12, 2023:
https://www.liebertpub.com/doi/full/10.1089/ast.2022.011
Direct In-Situ Capture, Separation and Visualization of Biological Particles with Fluid-Screen in the Context of Venus Life Finder Mission Concept Study
Evidence of chemical disequilibria and other anomalous observations in the
Venusian atmosphere motivate the search for life within the planet's temperate
clouds. To find signs of a Venusian aerial biosphere, a dedicated
astrobiological space mission is required. Venus Life Finder (VLF) missions
encompass unique mission concepts with specialized instruments to search for
habitability indicators, biosignatures and even life itself. A key in the
search for life is direct capture, concentration and visualization of particles
of biological potential. Here, we present a short overview of Fluid-Screen (FS)
technology, a recent advancement in the dielectrophoretic (DEP) microbial
particle capture, concentration and separation. FS is capable of capturing and
separating biochemically diverse particles, including multicellular molds,
eukaryotic cells, different species of bacteria and even viruses, based on
particle dielectric properties. In this short communication, we discuss the
possible implementation of Fluid-Screen in the context of the VLF missions,
emphasizing the unique science output of the Fluid-Screen instrument. FS can be
coupled with other highly sophisticated instruments such as an autofluorescence
microscope or a laser desorption mass spectrometer. We discuss possible
configurations of Fluid-Screen that upon modification and testing, could be
adapted for Venus. We discuss the unique science output of the FS technology
that can capture biological particles in their native state and hold them in
the focal plane of the microscope for the direct imaging of the captured
material. We discuss the challenges for the proposed method posed by the
concentrated sulfuric acid environment of Venus' clouds. While Venus' clouds
are a particularly challenging environment, other bodies of the solar system,
e.g., with liquid water present, might be especially suitable for Fluid-Screen
application.Comment: Published in Aerospace as a part of the Special Issue "The Search for
Signs of Life on Venus: Science Objectives and Mission Designs"
(https://www.mdpi.com/journal/aerospace/special_issues/Search_Life_Venus_Science_Objectives_Mission_Designs
Production of ammonia makes Venusian clouds habitable and explains observed cloud-level chemical anomalies.
The atmosphere of Venus remains mysterious, with many outstanding chemical connundra. These include the unexpected presence of ∼10 ppm O2 in the cloud layers, an unknown composition of large particles in the lower cloud layers, and hard to explain measured vertical abundance profiles of SO2 and H2O. We propose a hypothesis for the chemistry in the clouds that largely addresses all of the above anomalies. We include ammonia (NH3), a key component that has been tentatively detected both by the Venera 8 and Pioneer Venus probes. NH3 dissolves in some of the sulfuric acid cloud droplets, effectively neutralizing the acid and trapping dissolved SO2 as ammonium sulfite salts. This trapping of SO2 in the clouds, together with the release of SO2 below the clouds as the droplets settle out to higher temperatures, explains the vertical SO2 abundance anomaly. A consequence of the presence of NH3 is that some Venus cloud droplets must be semisolid ammonium salt slurries, with a pH of ∼1, which matches Earth acidophile environments, rather than concentrated sulfuric acid. The source of NH3 is unknown but could involve biological production; if so, then the most energy-efficient NH3-producing reaction also creates O2, explaining the detection of O2 in the cloud layers. Our model therefore predicts that the clouds are more habitable than previously thought, and may be inhabited. Unlike prior atmospheric models, ours does not require forced chemical constraints to match the data. Our hypothesis, guided by existing observations, can be tested by new Venus in situ measurements
Large Uncertainties in the Thermodynamics of Phosphorus (III) Oxide (PO) Have Significant Implications for Phosphorus Species in Planetary Atmospheres
Phosphorus (III) oxide (PO) has been suggested to be a major
component of the gas phase phosphorus chemistry in the atmospheres of gas giant
planets and of Venus. However, PO's proposed role is based on
thermodynamic modeling, itself based on values for the free energy of formation
of PO estimated from limited experimental data. Values of the standard
Gibbs free energy of formation (Go(g)) of PO in the literature
differ by up to ~656 kJ/mol, a huge range. Depending on which value is assumed,
PO may either be the majority phosphorus species present or be
completely absent from modeled atmospheres. Here, we critically review the
literature thermodynamic values and compare their predictions to observed
constraints on PO geochemistry. We conclude that the widely used values
from the NIST/JANAF database are almost certainly too low (predicting that
PO is more stable than is plausible). We show that, regardless of the
value of Go(g) for PO assumed, the formation of phosphine from
PO in the Venusian atmosphere is thermodynamically unfavorable. We
conclude that there is a need for more robust data on both the thermodynamics
of phosphorus chemistry for astronomical and geological modeling in general and
for understanding the atmosphere of Venus and the gas giant planets in
particular.Comment: Article published in ACS Earth Space Chem.
https://pubs.acs.org/doi/full/10.1021/acsearthspacechem.3c0001
Possibilities for an Aerial Biosphere in Temperate Sub Neptune-Sized Exoplanet Atmospheres
The search for signs of life through the detection of exoplanet atmosphere
biosignature gases is gaining momentum. Yet, only a handful of rocky exoplanet
atmospheres are suitable for observation with planned next-generation
telescopes. To broaden prospects, we describe the possibilities for an aerial,
liquid water cloud-based biosphere in the atmospheres of sub Neptune-sized
temperate exoplanets, those receiving Earth-like irradiation from their host
stars. One such planet is known (K2-18b) and other candidates are being
followed up. Sub Neptunes are common and easier to study observationally than
rocky exoplanets because of their larger sizes, lower densities, and extended
atmospheres or envelopes. Yet, sub Neptunes lack any solid surface as we know
it, so it is worthwhile considering whether their atmospheres can support an
aerial biosphere. We review, synthesize, and build upon existing research.
Passive microbial-like life particles must persist aloft in a region with
liquid water clouds for long enough to metabolize, reproduce, and spread before
downward transport to lower altitudes that may be too hot for life of any kind
to survive. Dynamical studies are needed to flesh out quantitative details of
life particle residence times. A sub Neptune would need to be a part of a
planetary system with an unstable asteroid belt in order for meteoritic
material to provide nutrients, though life would also need to efficiently reuse
and recycle metals. The origin of life may be the most severe limiting
challenge. Regardless of the uncertainties, we can keep an open mind to the
search for biosignature gases as a part of general observational studies of sub
Neptune exoplanets.Comment: Published in Universe: https://www.mdpi.com/2218-1997/7/6/17
The Venusian Lower Atmosphere Haze as a Depot for Desiccated Microbial Life: A Proposed Life Cycle for Persistence of the Venusian Aerial Biosphere
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.Comment: Open Access Astrobiology Articl
Source of phosphine on Venus—An unsolved problem
The tentative detection of ppb levels of phosphine (PH3) in the clouds of Venus was extremely surprising, as this reduced gas was not expected to be a component of Venus’ oxidized atmosphere. Despite potential confirmation in legacy Pioneer Venus mass spectrometry data, the detection remains controversial. Here we review the potential production of phosphine by gas reactions, surface and sub-surface geochemistry, photochemistry, and other nonequilibrium processes. None of these potential phosphine production pathways is sufficient to explain the presence of phosphine in Venus atmosphere at near the observed abundance. The source of atmospheric PH3 could be unknown geo- or photochemistry, which would imply that the consensus on Venus’ chemistry is significantly incomplete. An even more extreme possibility is that a strictly aerial microbial biosphere produces PH3. The detection of phosphine adds to the complexity of chemical processes in the Venusian environment and motivates better quantitation of the gas phase chemistry of phosphorus species and in situ follow-up sampling missions to Venus
Venusian phosphine:a 'Wow!' signal in chemistry?
The potential detection of ppb levels phosphine (PH3) in the clouds of Venus
through millimeter-wavelength astronomical observations is extremely surprising
as PH3 is an unexpected component of an oxidized environment of Venus. A
thorough analysis of potential sources suggests that no known process in the
consensus model of Venus' atmosphere or geology could produce PH3 at anywhere
near the observed abundance. Therefore, if the presence of PH3 in Venus'
atmosphere is confirmed, it is highly likely to be the result of a process not
previously considered plausible for Venusian conditions. The source of
atmospheric PH3 could be unknown geo- or photochemistry, which would imply that
the consensus on Venus' chemistry is significantly incomplete. An even more
extreme possibility is that strictly aerial microbial biosphere produces PH3.
This paper summarizes the Venusian PH3 discovery and the scientific debate that
arose since the original candidate detection one year ago.Comment: A short overview of the Venusian PH3 discovery and the scientific
debate that arose since the original candidate detection in September 2020.
Additional discussion of possible non-canonical sources of PH3 on Venus is
also included. arXiv admin note: text overlap with arXiv:2009.0649