Cloud Layer Of Venus Research Articles

Impact of the Turbulent Vertical Mixing on Chemical and Cloud Species in the Venus Cloud Layer

AbstractThe Venusian atmosphere hosts a 10 km deep convective layer that has been studied by various spacecrafts. However, the impact of the strong vertical mixing on the chemistry of this region is still unknown. This study presents the first realistic coupling between resolved small‐scale turbulence and a chemical network. The resulting vertical mixing is different for each species: those with longer chemical timescales will tend to be well‐mixed. Vertical eddy diffusion due to resolved convection motions was estimated, ranging from 102 to 104 m2/s for the 48–55 km convective layer, several orders of magnitude above the typically used value. In the 48–55 km convective layer, the impact of the small‐scale turbulence on the cloud layer boundaries was between 200 m and 1 km. The impact of turbulence on cloud chemistry is consistent with Venus Express/Visible and Infrared Thermal Imaging Spectrometer observations. The observability at the cloud‐top of small‐scale turbulence by VenSpec‐U spectrometer would be challenging.

Different Scenarios for the Origin and the Subsequent Succession of a Hypothetical Microbial Community in the Cloud Layer of Venus.

The possible existence of a microbial community in the venusian clouds is one of the most intriguing hypotheses in modern astrobiology. Such a community must be characterized by a high survivability potential under severe environmental conditions, the most extreme of which are very low pH levels and water activity. Considering different scenarios for the origin of life and geological history of our planet, a few of these scenarios are discussed in the context of the origin of hypothetical microbial life within the venusian cloud layer. The existence of liquid water on the surface of ancient Venus is one of the key outstanding questions influencing this possibility. We link the inherent attributes of microbial life as we know it that favor the persistence of life in such an environment and review the possible scenarios of life's origin and its evolution under a strong greenhouse effect and loss of water on Venus. We also propose a roadmap and describe a novel methodological approach for astrobiological research in the framework of future missions to Venus with the intent to reveal whether life exists today on the planet.

Introducing the Collection of Papers from the Second Workshop on Habitability of the Venus Cloud Layer and Related Research.

Introducing the Collection of Papers from the Second Workshop on Habitability of the Venus Cloud Layer and Related Research.

Multi-Channel Hyperspectral Imaging Spectrometer Design for Ultraviolet Detection in the Atmosphere of Venus

The spectroscopic detection of SO2 and unknown UV absorber substance in the H2SO4 cloud layer of Venus’ atmosphere is currently a focal point in the study of the habitability of Venusian atmospheric clouds. This paper addresses the simultaneous detection requirements of multiple substances in the ultraviolet range of Venus’ atmosphere and proposes a multi-channel hyperspectral imaging system design using pupil separation prisms and grating multilevel spectra. The system achieves a multi-channel design by splitting the entrance pupil of the telescope using prisms. Spectra from different channels are diffracted to the same detector through different orders of the grating. The system features a single spectrometer and detector, enabling simultaneous detection of spectra from different channels. It also boasts advantages such as compact size, ultra-high spectral resolution, and simultaneous multi-channel detection. The system design results indicate that within the working spectral range of three channels, the spectral resolution is better than 0.15 nm, surpassing previous in-orbit or current in-orbit planetary atmospheric detection spectrometers. With a Nyquist frequency of 56 lp/mm, the full-field MTF exceeds 0.7. The system’s smile is less than 0.05 μm, and the keystone is less than 0.04 μm, meeting the requirements for imaging quality.

Use of VEGA data to analyse balloon options for possible subsequent long endurance Venus cloud layer missions

Abstract The vertical motions and buoyancy variations of the two VEGA super-pressure balloons, flown in the middle cloud layer of Venus, are discussed. Using data derived from these 1985 nightside flights, estimates are made of the energy required to operate some alternative balloon platform schemes under consideration for future-proposed Venus-atmosphere in situ science missions. Despite the dissimilarity of these alternative platform schemes, the energy inputs required to operate each scheme on the Venus nightside are found to be similar. Estimates of the associated mass penalties of the associated energy sources are also made. Further investigation of a vertical propulsive assist scheme is recommended.

Lightning Flares in the Cloud Layer of Venus Detected in the Near-Infrared Range

Lightning Flares in the Cloud Layer of Venus Detected in the Near-Infrared Range

Searching for Life on Venus: History of the Problem and Basic Concepts

Venus has always been one of the priorities of the space research program in Russia. The history of successful investigations of Venus in the Soviet Union is primarily associated with delivering a whole series of spacecraft to it and implementing the first ever landing on its surface. In the last few years, the study of Venus in astrobiological direction has been rapidly developing. To date, a fairly large number of theoretical papers have been published, the main purpose of which is to estimate the possibility of the existence of living organisms on Venus. The most likely ecosystem, in which Earth-type organisms could develop, is considered to be a dense cloud layer of Venus. It is supposed that, in this layer, hypothetical microbial communities could exist in aerosols being a concentrated aqueous solution of sulfuric acid. Microorganisms in such a specific air habitat are to be exposed to several extreme factors at once, the main among which are very low values of pH and water activity. The principal strategies for survival under these conditions should be the availability of effective biochemical mechanisms of resistance to the impact of adverse environmental factors and the use of all possible ways of extracting energy in such an ecosystem to maintain the biomass of organisms at a level for stable reproduction.

Simulation of Venus Lightning‐I: Characterization of Free Radicals Generated in Venus Major Gas Mixture

AbstractA new Venus‐ESD‐Chamber (VEC) and peripheral systems were designed and built to simulate Venus lightning. It consists of three subsystems (a) electrostatic discharge (ESD) generation, (b) environmental pressure, temperature, gas composition control & monitoring, and (c) optical and non‐optical sensors. We conducted arc discharge experiments in air, in CO2, and in Venus major gas mixture (CO2‐N2, 96.5% ± 1.5%:3.5% ± 1.5%) under 10, 350, 700, and 1,000 mbar pressures, that correspond to the 50–75 km altitude range in the cloud layer of Venus. Plasma and Raman spectra, plus gas sensors, and GC‐MS were used to identify the ESD products and to semi‐quantify CO and O3 generated by ESD. We have found all species of free radicals that have been found in previous simulation studies using different discharge technologies, including some important species in CO2‐N2 system, nitrogen oxides and CN. In addition, we found three species (O3, N2+, and C2) that have not been previously reported. Our results suggest that electron flux and kinetic energy are the determining factors for the type of generated free radical species and gas pressure plays a less important role. We found that the quantity of CO changes with the type of ESD. The detection of O3 in this study suggests that lightning might be one of the sources of O3 observed in the Venusian atmosphere. OI emission line at 777.4 nm is the most prominent line in our plasma spectra of FD, consistent with the intense optical flash observed by the Lightning and Airglow Camera (LAC) on the Akatsuki mission.

In situ biochemical characterization of Venus cloud particles using a life-signature detection microscope.

Much of the information about the size and shape of aerosols forming haze and the cloud layer of Venus is obtained from indirect inferences from nephelometers on probes and from the analysis of the variation of polarization with the phase angle and the glory feature from images of Venus. The microscopic imaging of Venus' aerosols has recently been advocated. Direct measurements from a fluorescence microscope can provide information on the morphology, density, and biochemical characteristics of the particles; thus, fluorescence microscopy is attractive for in situ particle characterization of the Venus cloud layer. Fluorescence imaging of Venus cloud particles presents several challenges owing to the sulfuric acid composition and corrosive effects. In this article, we identify the challenges and describe our approach to overcoming them for a fluorescence microscope based on an in situ biochemical and physical characterization instrument for use in the clouds of Venus from a suitable aerial platform. We report that pH adjustment using alkali was effective for obtaining fluorescence images and that fluorescence attenuation was observed after the adjustment, even when the acidophile suspension in concentrated sulfuric acid was used as a sample.

Long duration flights in Venus’ atmosphere using passive solar hot air balloons

Solar balloons are a promising platform for providing multi-hour flights in and above the upper cloud layer of Venus. The temperature and pressure profiles from 55–75 km above the surface of Venus are very similar to Earth’s from sea level to approximately 30 km, the site of numerous terrestrial solar balloon missions. Additionally, Venus’ highly reflective cloud layer can provide a higher intensity of reflected solar radiation. An ideal solar balloon envelope incorporates a lightweight material that has a high absorbtivity in the visual spectrum, and a low emissivity in the infrared spectrum. The envelope then absorbs direct, reflected, and diffuse radiation, as well as infrared radiation, and heats up the internal balloon air through conduction, resulting in passive flight without the need for an external heat source or lifting gas. This work builds on previous high altitude and solar balloon models and adapts them for Venus’ atmosphere to explore their expected payload mass capacity and flight times. The possible equilibrium float altitudes for various system masses and solar zenith angles are compared between Earth and Venus. Finally, an Earth simulation is compared to terrestrial solar balloon mission data to validate the model and further demonstrate the feasibility of solar balloon flight on Venus.

Thermal Tides in the Upper Cloud Layer of Venus as Deduced From the Emission Angle Dependence of the Brightness Temperature by Akatsuki/LIR

AbstractThe brightness temperature of the Venus disk obtained by Longwave Infrared Camera (LIR) on board Akatsuki shows clear limb darkening at low and middle latitudes. The profile of limb brightness reflects the vertical distributions of atmospheric temperature and the optical thickness of the cloud particles. Horizontal distributions of brightness temperature obtained by LIR during ∼5.8 Venusian years were analyzed to investigate the vertical structure of the brightness temperature distribution above the cloud tops based on the emission angle dependence of the sensing altitude. Emission angles were converted to sensing altitudes by a radiative transfer calculation with nominal temperature and cloud particle distributions based on past observations. We show a local time‐altitude cross section of the brightness temperature deviation above the cloud tops for three latitudinal zones. The derived vertical amplitude distribution of the diurnal and semidiurnal tides above ∼68 km is mostly explained by the classical theory of thermal tides. A semidiurnal tide in which the phase shifts upstream with altitude is clearly seen in the equatorial region. By applying the dispersion relation of the internal gravity wave to the observed wave structure, it was found that the zonally averaged zonal wind velocity at altitudes of 66–71 km was approximately the same as the known superrotation velocity. By comparing the observed and simulated vertical phase structures, it is suggested that the tidal wave structure seen in the equatorial cloud tops is an aspect of upward propagation of a gravity wave generated in the upper cloud layer by solar heating.

Water-Sulfuric Acid Foam as a Possible Habitat for Hypothetical Microbial Community in the Cloud Layer of Venus.

The data available at the moment suggest that ancient Venus was covered by extensive bodies of water which could harbor life. Later, however, the drastic overheating of the planet made the surface of Venus uninhabitable for Earth-type life forms. Nevertheless, hypothetical Venusian organisms could have gradually adapted to conditions within the cloud layer of Venus—the only niche containing liquid water where the Earth-type extremophiles could survive. Here we hypothesize that the unified internal volume of a microbial community habitat is represented by the heterophase liquid-gas foam structure of Venusian clouds. Such unity of internal space within foam water volume facilitates microbial cells movements and trophic interactions between microorganisms that creates favorable conditions for the effective development of a true microbial community. The stabilization of a foam heterophase structure can be provided by various surfactants including those synthesized by living cells and products released during cell lysis. Such a foam system could harbor a microbial community of different species of (poly)extremophilic microorganisms that are capable of photo- and chemosynthesis and may be closely integrated into aero-geochemical processes including the processes of high-temperature polymer synthesis on the planet’s surface. Different complex nanostructures transferred to the cloud layers by convection flows could further contribute to the stabilization of heterophase liquid-gas foam structure and participate in chemical and photochemical reactions, thus supporting ecosystem stability.

Dataset: Thermal tides in the upper cloud layer of Venus as deduced from the emission angle dependence of the brightness temperature by Akatsuki/LIR

Dataset: Thermal tides in the upper cloud layer of Venus as deduced from the emission angle dependence of the brightness temperature by Akatsuki/LIR

Characterising atmospheric gravity waves on the nightside lower clouds of Venus: a systematic analysis

We present the detection and characterisation of mesoscale waves on the lower clouds of Venus using images from the Visible Infrared Thermal Imaging Spectrometer onboard the European Venus Express space mission and from the 2 μm camera (IR2) instrument onboard the Japanese space mission Akatsuki. We used image navigation and processing techniques based on contrast enhancement and geometrical projections to characterise morphological properties of the detected waves, such as horizontal wavelength and the relative optical thickness drop between crests and troughs. Additionally, we performed phase velocity and trajectory tracking of wave packets. We combined these observations to derive other properties of the waves such as the vertical wavelength of detected packets. Our observations include 13 months of data from August 2007 to October 2008, and the entire available data set of IR2 from January to November 2016. We characterised almost 300 wave packets across more than 5500 images over a broad region of the globe of Venus. Our results show a wide range of properties and are not only consistent with previous observations but also expand upon them, taking advantage of two instruments that target the same cloud layer of Venus across multiple periods. In general, waves observed on the nightside lower cloud are of a larger scale than the gravity waves reported in the upper cloud. This paper is intended to provide a more in-depth view of atmospheric gravity waves on the lower cloud and enable follow-up works on their influence in the general circulation of Venus.

The Venus Life Equation

Ancient Venus and Earth may have been similar in crucial ways for the development of life, such as liquid water oceans, land-ocean interfaces, favorable chemical ingredients and energy pathways. If life ever developed on, or was transported to, early Venus from elsewhere, it might have thrived, expanded and then survived the changes that have led to an inhospitable surface on Venus today. The Venus cloud layer may provide a refugium for extant life that persisted from an earlier more habitable surface environment. We introduce the Venus Life Equation - a theory and evidence-based approach to calculate the probability of extant life on Venus, L, using three primary factors of life: Origination, Robustness, and Continuity, or L = O x R x C. We evaluate each of these factors using our current understanding of Earth and Venus environmental conditions from the Archaean to the present. We find that the probability of origination of life on Venus would be similar to that of the Earth and argue that the other factors should be nonzero, comparable to other promising astrobiological targets in the solar system. The Venus Life Equation also identifies poorly understood aspects of Venus that can be addressed by direct observations with future exploration missions.

The Venus Life Equation.

Ancient Venus and Earth may have been similar in crucial ways for the development of life, such as liquid water oceans, land-ocean interfaces, favorable chemical ingredients, and energy pathways. If life ever developed on, or was transported to, early Venus from elsewhere, it might have thrived, expanded, and then survived the changes that have led to an inhospitable surface on Venus today. The Venus cloud layer may provide a refugium for extant life that persisted from an earlier more habitable surface environment. We introduce the Venus Life Equation (VLE)-a theory and evidence-based approach to calculate the probability of extant life on Venus, L, using three primary factors of life: Origination, Robustness, and Continuity, or L = O · R · C. We evaluate each of these factors using our current understanding of Earth and Venus environmental conditions from the Archean to the present. We find that the probability of origination of life on Venus would be similar to that of Earth, and argue that the other factors should be nonzero, comparable with other promising astrobiological targets in the solar system. The VLE also identifies poorly understood aspects of Venus that can be addressed by direct observations with future exploration missions.

Spectroscopy of OSSO and Other Sulfur Compounds Thought to be Present in the Venus Atmosphere.

The spectroscopy of cis-OSSO and trans-OSSO is explored and put into the context of the Venusian atmosphere, along with other sulfur compounds potentially present there, namely, S2O, C1-S2O2, trigonal-S2O2, and S3. UV-vis spectra were calculated using the nuclear ensemble approach. The calculated OSSO spectra are shown to match well with the 320-400 nm near-UV absorption previously measured on Venus, and we discuss the challenges of assigning OSSO as the Venusian near-UV absorber. The largest source of uncertainty is getting accurate concentrations of sulfur monoxide (3SO) in the upper cloud layer of Venus (60-70 km altitude) since the 3SO self-reaction is what causes cis- and trans-OSSO to form. Additionally, we employed the matrix-isolation technique to trap OSSO formed by microwave discharging a gas mixture of argon and SO2 and then depositing the mixture onto a cold window (6-12 K). Anharmonic vibrational transition frequencies and intensities were calculated at the coupled cluster level to corroborate the matrix-isolation FTIR spectra. The computationally calculated UV-vis and experimentally recorded IR spectra presented in this work aid future attempts at detecting these sulfur compounds in the Venusian atmosphere.

Global Structure of Thermal Tides in the Upper Cloud Layer of Venus Revealed by LIR on Board Akatsuki

AbstractLongwave Infrared Camera (LIR) on board Akatsuki first revealed the global structure of the thermal tides in the upper cloud layer of Venus. The data were acquired over three Venusian years, and the analysis was done over the areas from the equator to the midlatitudes in both hemispheres and over the whole local time. Thermal tides at two vertical levels were analyzed by comparing data at two different emission angles. Dynamical wave modes consisting of tides were identified; the diurnal tide consisted mainly of Rossby‐wave and gravity‐wave modes, while the semidiurnal tide predominantly consisted of a gravity‐wave mode. The revealed vertical structures were roughly consistent with the above wave modes, but some discrepancy remained if the waves were supposed to be monochromatic. In turn, the heating profile that excites the tidal waves can be constrained to match this discrepancy, which would greatly advance the understanding of the Venusian atmosphere.

Venus' Spectral Signatures and the Potential for Life in the Clouds.

The lower cloud layer of Venus (47.5–50.5 km) is an exceptional target for exploration due to the favorable conditions for microbial life, including moderate temperatures and pressures (∼60°C and 1 atm), and the presence of micron-sized sulfuric acid aerosols. Nearly a century after the ultraviolet (UV) contrasts of Venus' cloud layer were discovered with Earth-based photographs, the substances and mechanisms responsible for the changes in Venus' contrasts and albedo are still unknown. While current models include sulfur dioxide and iron chloride as the UV absorbers, the temporal and spatial changes in contrasts, and albedo, between 330 and 500 nm, remain to be fully explained. Within this context, we present a discussion regarding the potential for microorganisms to survive in Venus' lower clouds and contribute to the observed bulk spectra. In this article, we provide an overview of relevant Venus observations, compare the spectral and physical properties of Venus' clouds to terrestrial biological materials, review the potential for an iron- and sulfur-centered metabolism in the clouds, discuss conceivable mechanisms of transport from the surface toward a more habitable zone in the clouds, and identify spectral and biological experiments that could measure the habitability of Venus' clouds and terrestrial analogues. Together, our lines of reasoning suggest that particles in Venus' lower clouds contain sufficient mass balance to harbor microorganisms, water, and solutes, and potentially sufficient biomass to be detected by optical methods. As such, the comparisons presented in this article warrant further investigations into the prospect of biosignatures in Venus' clouds.

Winds in the Middle Cloud Deck From the Near‐IR Imaging by the Venus Monitoring Camera Onboard Venus Express

AbstractFor more than 8 years the Venus Monitoring Camera (VMC) onboard the Venus Express orbiter performed continuous imaging of the Venus cloud layer in UV, visible and near‐IR filters. We applied the correlation approach to sequences of the near‐IR images at 965 nm to track cloud features and determine the wind field in the middle and lower cloud (49–57 km). From the VMC images that spanned from December of 2006 through August of 2013 we derived zonal and meridional components of the wind field. In low‐to‐middle latitudes (5–65°S) the velocity of the retrograde zonal wind was found to be 68–70 m/s. The meridional wind velocity slowly decreases from peak value of +5.8 ± 1.2 m/s at 15°S to 0 at 65–70°S. The mean meridional speed has a positive sign at 5–65°S suggesting equatorward flow. This result, together with the earlier measurements of the poleward flow at the cloud tops, indicates the presence of a closed Hadley cell in the altitude range 55–65 km. Long‐term variations of zonal and meridional velocity components were found during 1,200 Earth days of observation. At 20° ± 5°S the zonal wind speed increases from −67.18 ± 1.81 m/s to −77.30 ± 2.49 m/s. The meridional wind gradually increases from +1.30 ± 1.82 m/s to +8.53 ± 2.14 m/s. Following Bertaux et al. (2016) we attribute this long‐term trend to the influence from the surface topography on the dynamical process in the atmosphere via the upward propagation of gravity waves that became apparent in the VMC observations due to slow drift of the Venus Express orbit over Aphrodite Terra.