arXiv subjects

Janusz J. Petkowski

Publications and source records attributed to Janusz J. Petkowski.

At least 19 recordsLinked to original sources

arXiv2026

A Model of UV-Blue Absorbance in Bulk Liquid of Venusian Cloud Aerosols Is Consistent with Efficient Organic Absorbers at High Concentrations

At visible wavelengths, Venus appears serene and pale-yellow, but since the 1920s, observers have noted high-contrast features in the ultraviolet. These features track the about 4-day superrotation of the upper cloud deck and vary widely over time and space. The identity of the UV absorber(s), active between at least 280 and 500 nm, remains unknown, as no proposed candidate fully matches all observational data. From remote observations of Venus, and accounting for light scattering by sub-micrometer droplets, we modeled the 365-455 nm absorbance per cm of the bulk liquids forming Venus's clouds. Assuming a uniform distribution in mode 1 and 2 particles across a 6 km layer below the cloud top at 65 km, we constrain the we constrained the decadic absorption coefficient within the modeled range to a peak at 375 nm to be 1278 per cm. This extremely high absorption coefficient implies the presence of a highly efficient absorber, for example, conjugated organics, at relatively high concentration, e.g., approx. 12 g/L for porphyrin-type pigments with molar absorption coefficient of approx. 100,000 per mole per cm. Inorganic absorbers, typically below 10,000 would either need to constitute a large portion of the aerosols or still not be sufficiently light-absorbing, even in pure form. We emphasize that all candidate absorbers must be evaluated against Venus's reflectance curve using (i) known molar absorption coefficients, (ii) realistic atmospheric distributions, and (iii) appropriate particle size distributions. The planned Rocket Lab mission will test the hypothesis of organics in Venus's clouds.

astro-ph.EP↗

arXiv2026

The Viability of Life in Helium-Dominated Exoplanet Atmospheres

Helium is the second most abundant element in the Universe, yet helium-dominated atmospheres are rarely considered as environments for life. Two assumptions have contributed to this neglect: helium is expected to escape from rocky planets together with hydrogen, and Earth itself lacks a substantial helium envelope. Recent observations and atmospheric evolution models, indicate that rocky exoplanets can retain helium-dominated atmospheres. Here we make the case for life in such environments by synthesizing a largely overlooked body of laboratory research on life in helium-dominated atmospheres. Every organism studied, including bacteria, fungi, protozoa, microalgae, plants, and animals tolerates helium-dominated atmospheres when supplied with essential metabolic requirements. Across a range of pressures, helium has shown no demonstrated toxicity and no fundamental barrier to metabolism, cell division, photosynthesis, nitrogen fixation, or coordinated multicellular activity, including in humans. Helium-dominated atmospheres therefore constitute a viable and underrecognized planetary environment for life. Helium is chemically inert and spectroscopically unobtrusive, so the bulk atmosphere would neither contribute to the chemical destruction of biosignature gases nor strongly obscure their spectral features. Helium-dominated atmospheres also have low mean molecular weights and large scale heights, strengthening spectral features in transmission and improving remote detectability.

astro-ph.EP↗

arXiv2026

Ionic Liquid Biospheres

Liquid is a fundamental requirement for life as we understand it, but whether that liquid has to be water is not known. We propose the hypothesis that ionic liquids (ILs) and deep eutectic solvents (DES) constitute a class of non-aqueous planetary liquids capable of persisting on a wide range of bodies where stable liquid water cannot exist. This hypothesis is motivated by key physical properties of ILs and DES. Many exhibit vapor pressures orders of magnitude lower than that of water and remain liquid across exceptionally wide temperature ranges, from cryogenic to well above terrestrial temperatures. These properties permit stable liquids to exist where liquid water would rapidly evaporate or freeze and outside of bulk phases as persistent microscale reservoirs-such as thin films and pore-filling droplets. In other words, ILs and DES can persist in environments without requiring oceans, thick atmospheres, or narrowly regulated climate conditions. We further hypothesize that ILs and DES could act as solvents for non-Earth-like life. Our hypothesis ex-tends to the idea that ILs and DES could enable prebiotic chemistry by providing long-lived, protective liquid environments for complex organic molecules on bodies such as comets and asteroids, where liquid water is absent. Based on the occurrence of DES-like mixtures as protective intracellular liquids in desiccation-tolerant plants, we propose that ILs and DES might be solvents that life elsewhere purposefully evolves. We review protein and other biomolecule studies in ILs and DES and outline planetary environments in which ILs and DES might occur by discussing available anions and cations. We present strategies to advance the IL/DES solvent hypothesis using laboratory studies, computational chemistry, planetary missions, analysis of existing spectroscopic datasets, and modeling of liquid microniches and chemical survival on small bodies.

astro-ph.EP↗

arXiv2025

Warm, water-depleted rocky exoplanets with surface ionic liquids: A proposed class for planetary habitability

The discovery of thousands of exoplanets and the emergence of telescopes capable of exoplanet atmospheric characterization have intensified the search for habitable worlds. Due to selection biases, many exoplanets under study are planets deemed inhospitable because their surfaces are too warm to support liquid water. We propose that such planets could still support life through ionic liquids: Liquid salts with negligible vapor pressure that can persist on warm planets with thin atmospheres, where liquid water cannot. Ionic liquids have not previously been considered as naturally occurring substances, and thus have not been discussed in planetary science. We demonstrate in laboratory experiments that ionic liquids can form from planetary materials: Sulfuric acid combined with nitrogen-containing organic molecules. Sulfuric acid can be volcanic in origin, and organic compounds are commonly found on planetary bodies. The required planetary surface is water-depleted and must support sulfuric acid transiently in liquid phase to dissolve organics, followed by evaporation of excess liquid, conditions spanning approximately 300 K at 10^-7 atm to 350-470 K at 0.01 atm. Because ionic liquids have extremely low vapor pressures, they are not prone to evaporation, allowing small droplets or pools to persist without ocean-like reservoirs. Ionic liquids' minuscule vapor pressure at room temperature suggests possible stability on planets with negligible atmospheres, shielded by magnetic fields or rock crevices against harsh cosmic radiation. Ionic liquids can stably dissolve enzymes and other biomolecules, enabling biocatalysis and offering a plausible solvent for life, broadening the definition of habitable worlds.

astro-ph.EP↗

arXiv2025

The Diversity of Exoplanetary Environments and the Search for Signs of Life Beyond Earth

Thousands of exoplanets orbit nearby stars, showcasing a remarkable diversity in mass, size, and orbits. With the James Webb Space Telescope now operational, we are observing exoplanet atmospheres and aiming to reach down to small, habitable-zone exoplanets in search of signs of habitability and possibly even biosignature gases. Given the scarcity of targets, it is imperative to embrace the known diversity and consider the range of exoplanets that might host life. We review how Earth life interacts with various atmospheric gases, noting that bacteria can survive in high concentrations of gases such as H2, He, CO2, and CO. Additionally, we consider the potential for life in alternative solvents and in cloud biospheres where rocky surfaces are excessively hot, as well as in hypothesized planetary global oceans. We highlight that life fundamentally requires metal ions for catalytic reactions, suggesting that environments without surface contact need meteoritic delivery to provide these essential elements. Despite today's observational limits, a suite of next-generation telescopes is being designed specifically for exoplanet studies, promising to expand our capabilities and understanding in the future.

astro-ph.EP↗

arXiv2025

Prospects for Detecting Signs of Life on Exoplanets in the JWST Era

The search for signs of life in the Universe has entered a new phase with the advent of the James Webb Space Telescope (JWST). Detecting biosignature gases via exoplanet atmosphere transmission spectroscopy is in principle within JWST's reach. We reflect on JWST's early results in the context of the potential search for biological activity on exoplanets. The results confront us with a complex reality. Established inverse methods to interpret observed spectra-already known to be highly averaged representations of intricate 3D atmospheric processes-can lead to disparate interpretations even with JWST's quality of data. Characterizing rocky or sub-Neptune-size exoplanets with JWST is an intricate task, and moves us away from the notion of finding a definitive "silver bullet" biosignature gas. Indeed, JWST results necessitate us to allow "parallel interpretations" that will perhaps not be resolved until the next generation of observatories. Nonetheless, with a handful of habitable-zone planet atmospheres accessible given the anticipated noise floor, JWST may continue to contribute to this journey by designating a planet as biosignature gas candidate. To do this we will need to sufficiently refine our inverse methods and physical models for confidently quantifying specific gas abundances and constraining the atmosphere context. Looking ahead, future telescopes and innovative observational strategies will be essential for the reliable detection of biosignature gases.

astro-ph.EP↗

arXiv2025

Simple lipids form stable higher-order structures in concentrated sulfuric acid

Venus has become a target of astrobiological interest because it is physically accessible to direct exploration, unlike exoplanets. So far this interest has been motivated not by the explicit expectation of finding life but rather by a desire to understand the limits of biology. The venusian surface is sterilizing, but the cloud deck includes regions with temperatures and pressures conventionally considered compatible with life. However, the venusian clouds are thought to consist of concentrated sulfuric acid. To determine if any fundamental features of life as we understand them here on Earth could in principle exist in these extreme solvent conditions, we tested several simple lipids for resistance to solvolysis and their ability to form structures in concentrated sulfuric acid. We find that single-chain saturated lipids with sulfate, alcohol, trimethylamine, and phosphonate head groups are resistant to sulfuric acid degradation at room temperature. Furthermore, we find that they form stable higher-order structures typically associated with lipid membranes, micelles, and vesicles. Finally, results from molecular dynamics simulations suggest a molecular explanation for the observed robustness of the lipid structures formed in concentrated sulfuric acid. We conclude with implications for the study of Venus as a target of experimental astrobiology.

physics.chem-ph↗

arXiv2024

Alternative solvents for life: framework for evaluation, current status and future research

Life is a complex, dynamic chemical system that requires a dense fluid solvent in which to take place. A common assumption is that the most likely solvent for life is liquid water, and some researchers argue that water is the only plausible solvent. However, a persistent theme in astrobiological research postulates that other liquids might be cosmically common, and could be solvents for the chemistry of life. In this paper we present a new framework for the analysis of candidate solvents for life, and deploy this framework to review substances that have been suggested as solvent candidates. We categorize each solvent candidate through four criteria: occurrence, solvation, solute stability and solvent chemical functionality. Our semi-quantitative approach addresses all the requirements for a solvent not only from the point of view of its chemical properties but also from the standpoint of their biochemical function. Only the protonating solvents fulfil all the chemical requirements to be a solvent for life, and of those only water and concentrated sulfuric acid are also likely to be abundant in a rocky planetary context. Among the non-protonating solvents liquid CO2 stands out as a planetary solvent, and its potential as a solvent for life should be explored. We conclude with a discussion of whether it is possible for a biochemistry to change solvents, as an adaptation to radical changes in a planet's environment. Our analysis provides the basis for prioritizing future experimental work exploring potential complex chemistry on other planets.

astro-ph.EP↗

arXiv2024

Can Isotopologues Be Used as Biosignature Gases in Exoplanet Atmospheres?

Isotopologue ratios are anticipated to be one of the most promising signs of life that can be observed remotely. On Earth, carbon isotopes have been used for decades as evidence of modern and early metabolic processes. In fact, carbon isotopes may be the oldest evidence for life on Earth, though there are alternative geological processes that can lead to the same magnitude of fractionation. However, using isotopologues as biosignature gases in exoplanet atmospheres presents several challenges. Most significantly, we will only have limited knowledge of the underlying abiotic carbon reservoir of an exoplanet. Atmospheric carbon isotope ratios will thus have to be compared against the local interstellar medium or, better yet, their host star. A further substantial complication is the limited precision of remote atmospheric measurements using spectroscopy. The various metabolic processes which cause isotope fractionation cause less fractionation than anticipated measurement precision (biological fractionation is typically 2 to 7%). While this level of precision is easily reachable in the laboratory or with special in situ instruments, it is out of reach of current telescope technology to measure isotope ratios for terrestrial exoplanet atmospheres. Thus, gas isotopologues are poor biosignatures for exoplanets given our current and foreseeable technological limitations.

astro-ph.EP↗

arXiv2024

Astrobiological Potential of Venus Atmosphere Chemical Anomalies and Other Unexplained Cloud Properties

Long-standing unexplained Venus atmosphere observations and chemical anomalies point to unknown chemistry but also leave room for the possibility of life. The unexplained observations include several gases out of thermodynamic equilibrium (e.g. tens of ppm O2, the possible presence of PH3 and NH3, SO2 and H2O vertical abundance profiles), an unknown composition of large, lower cloud particles, and the "unknown absorber(s)". Here we first review relevant properties of the Venus atmosphere and then describe the atmospheric chemical anomalies and how they motivate future astrobiology missions to Venus.

astro-ph.EP↗

arXiv2024

Atmospheric carbon depletion as a tracer of water oceans and biomass on temperate terrestrial exoplanets

The conventional observables to identify a habitable or inhabited environment in exoplanets, such as an ocean glint or abundant atmospheric O$_2$, will be challenging to detect with present or upcoming observatories. Here we suggest a new signature. A low carbon abundance in the atmosphere of a temperate rocky planet, relative to other planets of the same system, traces the presence of substantial amount of liquid water, plate tectonic and/or biomass. We show that JWST can already perform such a search in some selected systems like TRAPPIST-1 via the CO$_2$ band at $4.3\,\rm μm$, which falls in a spectral sweet spot where the overall noise budget and the effect of cloud/hazes are optimal. We propose a 3-step strategy for transiting exoplanets: 1) detection of an atmosphere around temperate terrestrial planets in $\sim 10$ transits for the most favorable systems, (2) assessment of atmospheric carbon depletion in $\sim 40$ transits, (3) measurements of O$_3$ abundance to disentangle between a water- vs biomass-supported carbon depletion in $\sim100$ transits. The concept of carbon depletion as a signature for habitability is also applicable for next-generation direct imaging telescopes.

astro-ph.EP↗

arXiv2024

Stability of 20 Biogenic Amino Acids in Concentrated Sulfuric Acid: Implications for the Habitability of Venus' Clouds

Scientists have long speculated about the potential habitability of Venus, not at the 700K surface, but in the cloud layers located at 48-60 km altitudes, where temperatures match those found on Earth's surface. However, the prevailing belief has been that Venus' clouds cannot support life due to the cloud chemical composition of concentrated sulfuric acid-a highly aggressive solvent. In this work, we study 20 biogenic amino acids at the range of Venus' cloud sulfuric acid concentrations (81% and 98% w/w, the rest water) and temperatures. We find 19 of the biogenic amino acids we tested are either unreactive (13 in 98% w/w and 12 in 81% w/w) or chemically modified in the side chain only, after four weeks. Our major finding, therefore, is that the amino acid backbone remains intact in concentrated sulfuric acid. These findings significantly broaden the range of biologically relevant molecules that could be components of a biochemistry based on a concentrated sulfuric acid solvent.

astro-ph.EP↗

arXiv2023

Fully fluorinated non-carbon compounds NF3 and SF6 as ideal technosignature gases

Waste gas products from technological civilizations may accumulate in an exoplanet atmosphere to detectable levels. We propose nitrogen trifluoride (NF3) and sulfur hexafluoride (SF6) as ideal technosignature gases. Earth life avoids producing or using any N-F or S-F bond-containing molecules and makes no fully fluorinated molecules with any element. NF3 and SF6 may be universal technosignatures owing to their special industrial properties, which unlike biosignature gases, are not species-dependent. Other key relevant qualities of NF3 and SF6 are: their extremely low water solubility, unique spectral features, and long atmospheric lifetimes. NF3 has no non-human sources and was absent from Earth's pre-industrial atmosphere. SF6 is released in only tiny amounts from fluorine-containing minerals, and is likely produced in only trivial amounts by volcanic eruptions. We propose a strategy to rule out SF6's abiotic source by simultaneous observations of SiF4, which is released by volcanoes in an order of magnitude higher abundance than SF6. Other fully fluorinated human-made molecules are of interest, but their chemical and spectral properties are unavailable. We summarize why life on Earth-and perhaps life elsewhere-avoids using F. We caution, however, that we cannot definitively disentangle an alien biochemistry byproduct from a technosignature gas.

astro-ph.EP↗

arXiv2023

Stability of nucleic acid bases in concentrated sulfuric acid: Implications for the habitability of Venus' clouds

What constitutes a habitable planet is a frontier to be explored and requires pushing the boundaries of our terracentric viewpoint for what we deem to be a habitable environment. Despite Venus' 700 K surface temperature being too hot for any plausible solvent and most organic covalent chemistry, Venus' cloud-filled atmosphere layers at 48 to 60 km above the surface hold the main requirements for life: suitable temperatures for covalent bonds; an energy source (sunlight); and a liquid solvent. Yet, the Venus clouds are widely thought to be incapable of supporting life because the droplets are composed of concentrated liquid sulfuric acid-an aggressive solvent that is assumed to rapidly destroy most biochemicals of life on Earth. Recent work, however, demonstrates that a rich organic chemistry can evolve from simple precursor molecules seeded into concentrated sulfuric acid, a result that is corroborated by domain knowledge in industry that such chemistry leads to complex molecules, including aromatics. We aim to expand the set of molecules known to be stable in concentrated sulfuric acid. Here, we show that nucleic acid bases adenine, cytosine, guanine, thymine, and uracil, as well as 2,6-diaminopurine and the "core" nucleic acid bases purine and pyrimidine, are stable in sulfuric acid in the Venus cloud temperature and sulfuric acid concentration range, using UV spectroscopy and combinations of 1D and 2D 1H 13C 15N NMR spectroscopy. The stability of nucleic acid bases in concentrated sulfuric acid advances the idea that chemistry to support life may exist in the Venus cloud particle environment.

physics.chem-ph↗

arXiv2023

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.

astro-ph.EP↗

arXiv2023

Large Uncertainties in the Thermodynamics of Phosphorus (III) Oxide (P$_4$O$_6$) Have Significant Implications for Phosphorus Species in Planetary Atmospheres

Phosphorus (III) oxide (P$_4$O$_6$) 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, P$_4$O$_6$'s proposed role is based on thermodynamic modeling, itself based on values for the free energy of formation of P$_4$O$_6$ estimated from limited experimental data. Values of the standard Gibbs free energy of formation ($Δ$Go(g)) of P$_4$O$_6$ in the literature differ by up to ~656 kJ/mol, a huge range. Depending on which value is assumed, P$_4$O$_6$ 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 P$_4$O$_6$ geochemistry. We conclude that the widely used values from the NIST/JANAF database are almost certainly too low (predicting that P$_4$O$_6$ is more stable than is plausible). We show that, regardless of the value of $Δ$Go(g) for P$_4$O$_6$ assumed, the formation of phosphine from P$_4$O$_6$ 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.

astro-ph.EP↗

arXiv2023

Recovering Phosphine in Venus' Atmosphere from SOFIA Observations

Searches for phosphine in Venus' atmosphere have sparked a debate. Cordiner et al. 2022 analyse spectra from the Stratospheric Observatory For Infrared Astronomy (SOFIA) and infer <0.8 ppb of PH3. We noticed that some spectral artefacts arose from non-essential calibration-load signals. By-passing these signals allows simpler post-processing and a 5.7σ candidate detection, suggesting approx. 3 ppb of PH3 above the clouds. Compiling six phosphine results hints at an inverted abundance trend: decreasing above the clouds but rising again in the mesosphere from some unexplained source. However, no such extra source is needed if phosphine is undergoing destruction by sunlight (photolysis), to a similar degree as on Earth. Low phosphine values/limits are found where the viewed part of the super-rotating Venusian atmosphere had passed through sunlight, while high values are from views moving into sunlight. We suggest Venusian phosphine is indeed present, and so merits further work on models of its origins.

astro-ph.EP↗

arXiv2022

Venus Life Finder Habitability Mission: Motivation, Science Objectives, and Instrumentation

For over half a century, scientists have contemplated the potential existence of life within the clouds of Venus. Unknown chemistry leaves open the possibility that certain regions of the Venusian atmosphere are habitable. In situ atmospheric measurements with a suite of modern instruments can determine whether the cloud decks possess the characteristics needed to support life as we know it. The key habitability factors are cloud particle droplet acidity and cloud-layer water content. We envision an instrument suite to measure not only the acidity and water content of the droplets (and their variability) but additionally to confirm the presence of metals and other non-volatile elements required for life's metabolism, verify the existence of organic material, and search for biosignature gases as signs of life. We present an astrobiology-focused mission, science goals, and instruments that can be used on both a large atmospheric probe with a parachute lasting about one hour in the cloud layers (40 to 60 km) or a fixed-altitude balloon operating at about 52 km above the surface. The latter relies on four deployable mini probes to measure habitability conditions in the lower cloud region. The mission doubles as a preparation for sample return by determining whether a subset of cloud particles is non-liquid as well as characterizing the heterogeneity of the cloud particles, thereby informing sample collection and storage methods for a return journey to Earth.

astro-ph.IM↗