This study explores an approach for identifying and characterizing sites on Venus where a future lander mission could attain a high probability of safe landing through a synthesis of Venera surface ...panoramas, Magellan radar properties, and existing global geological maps of the Venus surface. Surface panoramas from the Venera 9 and Venera 13 landers were used to define rock size distributions and to calculate the probability of a hazardous rock encounter for a reference Venus lander design at these specific landing sites. This surface analysis formed the basis and rationale for the development of a set of global filters seeking to identify “safe” 150-km-diameter landing ellipses with Magellan radiophysical properties including root mean square slope, radar backscatter coefficient, and emissivity values similar to the most benign regional plains unit (rp2) mapped by Ivanov and Head 2011 within the Venera 13 landing site. Using this method, 178 unique ellipses for which >95% of pixels exhibited rms slope and radar backscatter coefficient values similar to the Venera 13 rp2 unit were identified across the Venus surface. Of these ellipses, 36 also contained >95% of pixels with similar emissivity values as the Venera 13 rp2 unit. “Safe” ellipses identified by this method were predominantly composed of regional plains, shield plains, and smooth plains as defined in the Venus global geologic map of Ivanov and Head 2011. Although the method developed in this study for identifying and characterizing safe landing sites on Venus requires several assumptions regarding the correlation of orbiter radar data to surface properties relevant to lander safety, this approach provides a best effort starting point integrating available data for the systematic, relatively objective, and automatic identification of safe landing sites on Venus.
•This work develops a systematic and objective assessment and selection of “safe” landing sites for future Venus landers.•Existing surface panoramas from the Venera 9 and 13 landers were used to characterize local rock size distributions.•Areas of the surface that are morphologically and radiophysically similar to the Venera 13 landing area are identified with a filter.
•Developed a 1D-photochemical model for Venusian ionosphere.•The neutral density model, VTS3 represents well the Venus atmosphere in the low, medium and high solar activity conditions.•The inclusion ...of VTS3 model significantly improved IonA model output by matching the modeled V2 peak density heights with VeRa observations.•The in-house developed 1D-PCM not only reproduced VeRa observed V2 peak altitude, the density of the peak V2 layer was also represented well.•The neutral density variation controlls the V2 layer peak density height , whereas the peak density of the V2 layer is determined by the complex chemical reactions.
Using an in-house developed one dimensional photo-chemical model (1D-PCM), which considers production and loss of 11 ions namely, CO2+, CO+, C+, N2+, N+, He+, O+(2D), O+(2P), O+(4S), O2+ and NO+, characteristics of the V2 layer in the Venus ionosphere has been studied. It is noted that existing ionospheric model for the Venus ionosphere, such as the IonA (Ionization in Atmospheres) model, not only over/under estimate the peak electron density of V2 layer, it also has significant departures from the observations on the solar zenith angle and solar activity control. The IonA model uses VenusGRAM model (Venus Global Reference Atmosphere Model) as input for the neutral density and temperature and considers Venus atmosphere consisting of CO2, O, and N2 molecules only. Further, it oversimplifies the ion chemistry by assuming Venus ionosphere to have O2+ as the only dominant ion species. Using VTS3 model, an empirical model based on measurements from Orbiter Neutral Mass Spectrometer on Pioneer Venus Orbiter (PVO) which considers profiles of six neutrals (CO2, O, CO, He, N, and N2), we modified IonA model, named as IonA-VTS3, to find that it reproduced the altitude of V2 peak electron density (hmV2) quite well. However, the model still lacked in reproducing observed peak V2 electron density (NmV2). The in-house developed one dimensional photo-chemical model (1D-PCM) not only estimated NmV2 accurately, the hmV2 was also reproduced quite well. Comparison of Venera and PVO radio occultation measurements with 1D-PCM and IonA-VTS3 calculations reveals the role of complex chemical reactions in determining the features of peak altitude and density of V2 layer during different solar activity periods. We surmised that differences in the observed and IonA modeled peak V2 layer altitudes were due to the limitations associated with VenusGRAM neutral density model. It shows that variations in the neutral density controls the V2 layer peak density height. 1D-PCM calculations also showed that the complex chemistry including production and loss reactions of 11 ions could reproduce the variations in the peak density of Venusian ionosphere during different solar activity conditions. It suggests that the ion-chemistry has wider control over the peak plasma density in the Venus ionosphere.
Our understanding of the Venusian surface composition is limited to the in-situ bulk rock chemical analyses collected by the Vega and Venera missions. However, these analyses have exceedingly large ...analytical uncertainties – up to 50% by weight (1σ) for certain oxide components. In this study, we use the Venera 14 lander data and apply a Monte Carlo approach to assess how significant uncertainties affect modeling of lava solidification. Thermodynamic modeling of mineral-melt equilibria is conducted over 1,000 iterations of simulated bulk composition within the Gaussian probabilistic bounds of the reported analytical uncertainty along a cooling path from 1350°C to 950°C, with a fixed pressure of 90 bars. The results are used to calculate melt and apparent viscosity (ηmelt and ηapp, respectively). Despite the significant analytical uncertainty of the lander data, lava viscosity is tightly constrained. Mean log ηmelt increases from 1.65 ± 0.46 Pas at 1350°C to 8.57 ± 1.42 Pas at 950°C (1σ). Log ηapp is less well-defined due to increased scatter in crystal fraction with solidification, increasing to 17.7 ± 1.3 Pas at 950°C (γ=10−6 s−1). A significant increase in ηapp occurs between 1240°C and 1080°C due to a rapid increase in crystal mass fraction (Φ increases from ∼0.05 at 1250°C to 0.8 at ∼1100°C). Slow cooling through this 150°C window must occur so as to not drastically increase lava viscosity and impede flow. These results show that despite limited geochemical data and large analytical uncertainties, reasonable constraints for the physical and chemical evolution of lava solidification can be obtained. Most of the Venusian surface is composed of volcanic plains and rises, containing abundant landforms characteristic of fluid basaltic lava. Our results provide new insights into the crystallization processes in Venusian lava flows, which are fundamental for understanding Venusian igneous processes, geodynamics, and resurfacing. This work provides a necessary framework for future thermorheological flow models to determine flow volume and effusion rates.
•Rapid increase in melt viscosity occurs with onset of pyroxene crystallization.•Large geochemical uncertainties are considered through a Monte Carlo approach.•Results suggest tight viscosity constraints despite the large analytical uncertainty.
A problem of determining attainable landing sites on the surface of Venus is an essential part of the Venera-D project aimed to explore the planet using a lander. This problem appears due to the ...inability for the descent module to land at any point on the surface of Venus because of the short duration of the launch window (about 2 weeks from the optimal launch date), as well as restrictions on the maximum permissible overload. An additional factor affecting the reduction of attainable landing sites is the low angular velocity of Venus’ own rotation. This study proposes a new approach to expand the attainable landing areas. The approach is based on the use of the gravitational field of Venus to transfer the spacecraft to an orbit resonant to the Venusian one with a ratio of periods of 1:1. All the simulations were performed at the patched conic approximation. As an example, we considered a flight to Venus at launch in 2029 or 2031. For both cases maps of attainable landing areas on the Venus surface were plotted. It has been demonstrated that there is always at least one launch date within the launch window allowing the spacecraft to reach almost any point on the surface of Venus. It is shown that the application of the proposed approach makes it possible to achieve a significant expansion of the attainable landing areas (over 70% of the surface) and, in some cases, provide access to any point on the surface of Venus. However, the price of this advantage is an increase in the flight duration by one Venusian year.
•The method of expanding attainable areas on the Venus surface has been developed.•The landing areas on the Venus surface are calculated for launch in 2029 and 2031.•The use of gravity assist of Venus is proposed for expansion of landing areas.
•The rock analyzed at the Venera 8 landing site is thought to be silicic.•Fractional crystallization of Venusian basalt can produce the theoretical Venera 8 rock.•It is possible that sialic crust was ...encountered at the Venera 8 landing site.
The surface rock composition measured by gamma (γ)-ray spectrometry at the Venera 8 landing site has anomalously high Th (6.5 ± 2.2 ppm) and U (2.2 ± 0.7 ppm) concentrations with respect to the material analyzed at other landing sites (Vega 1, Vega 2, Venera 9, Venera 10). A calculated bulk rock composition of Venera 8, constrained by the measured Th, U and K2O (4.0 ± 1.2 wt%) contents, is similar to silicic to intermediate rocks (diorite/granodiorite) that are typical of terrestrial convergent margins (magnesian, calc-alkalic). In this study, major and trace elemental modeling is applied in order to determine if the calculated whole rock composition of Venera 8 can be derived from a parental magma composition similar to Venusian basalt. The modeling results indicate that polybaric fractional crystallization of a hydrous (H2O = 0.4 wt%) and relatively oxidizing (ΔFMQ + 0.7) parental composition similar to Venera 14 basalt can yield residual silicic liquids that match the calculated Venera 8 whole rock composition. The measured Th and U concentrations can also be reproduced within the data uncertainty. Although Venus lacks modern Earth-style plate tectonics, magnesian, calc-alkalic compositions are common within Archean greenstone belts and some rift settings (Haida Gwaii). Consequently, it is possible that the Venera 8 probe encountered a fragment of crust that resembles a terrestrial greenstone belt.
On Venus, understanding of surface-atmosphere interactions resulting from chemical weathering is both critically important for constraining atmospheric chemistry and relative ages of surface features ...and multifaceted, requiring integration of diverse perspectives and disciplines of study. This paper evaluates the issue of surface alteration on Venus using multiple lines of evidence. Surface chemistry from Venera and Vega landers is inconsistent with significant breakdown from atmospheric interactions, with <2.0 wt% S or less observed. Consideration of kinetics and breakdown of basalt under Venus conditions indicates diffusion of Ca > Fe > Mg toward the oxidizing Venus atmosphere, favoring creation of anhydrite and carbonate-rich surfaces on basalts with minor addition of hematite. When related to Venus-analog experiments, the kinetic calculations suggest a maximum coating of ~30 μm over 500,000 years. These changes would result in a slight overall volume increase in the outermost surface materials, which in turn decreases surface rock FeO contents. Those variations can be detected from orbit because emissivity is correlated with total FeO, and the predicted magnitudes are consistent with Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) observations. Models of anhydrite and hematite coatings on basalt mixtures suggest that changes in emissivity (ε) spectra due to chemical weathering can result in ca. <0.08 shifts in total emissivity. Such gradations are small compared to the first-order effect of bulk composition on emissivity, which can cause up to ~0.80 emissivity shifts. For all these reasons, there is at present no evidence to suggest that impenetrable coatings of either hematite (ε = 0.8) or anhydrite (ε = 0.1) are present on Venus. Orbital measurements of surface emissivity on a global scale could therefore produce not only a map of rock type and surface composition based on transition metal contents (largely FeO) (Helbert et al., 2020) but also provide local scale assessments of fresh vs. mature lava flows on the surface.
•The weight percentage of sulfur measured on the Venus surface implies only partial reaction with atmosphere.•Anhydrite/carbonate coatings form very slowly at the surface-atmosphere interface.•Hematite surface coatings on Venus are highly unlikely at surface temperatures.•Basalt weathering causes small emissivity variations visible at local scales.•Emissivity shifts result from dilution of bulk rock FeO by atmospheric components.
•The primary melt composition of the Venera 14 basalt is high-Mg basalt to picrite.•The TP estimates of Venera 14 basalt range from 1310 °C to 1440°C.•The TP of Venera 14 basalt is similar to ambient ...terrestrial mantle.
The crater density and distribution of Venus indicates the average surface age is younger (≤1Ga) than most terrestrial planets and satellites in the Solar System. The type and rate (i.e. equilibrium, catastrophic or differential) of volcanism associated with the stagnant lid tectonic system of Venus is a first order problem that has yet to be resolved but is directly related to the thermal conditions of the mantle. The calculated primary melt composition of basalt at the Venera 14 landing site is high-Mg basalt to picrite with a mantle potential temperature estimate similar to terrestrial ambient mantle (1370±70°C). The calculated accumulated fractional melting curves indicate the olivine compositions from the melt have Mg# of 89–91. The results show that the thermal regime required to generate the primary melt composition of the Venera 14 basalt was not anomalously high (i.e. mantle-plume system) but rather consistent with a lithospheric tensional rift system. The juxtaposition of high thermal regime structures (e.g. Beta Regio) and ‘ambient’ mantle potential temperature estimates of the Venera 14 basalt suggests that the relatively young surface of Venus is the result of volcanism from a combination of thermal systems that resurfaced the planet at variable rates.
The superrotation of the atmospheres of Venus and Titan has puzzled dynamicists for many years and seems to put these planets in a very different dynamical regime from most other planets. In this ...review, we consider how to define superrotation objectively and explore the constraints that determine its occurrence. Atmospheric superrotation also occurs elsewhere in the Solar System and beyond, and we compare Venus and Titan with Earth and other planets for which wind estimates are available. The extreme superrotation on Venus and Titan poses some difficult challenges for numerical models of atmospheric circulation, much more difficult than for more rapidly rotating planets such as Earth or Mars. We consider mechanisms for generating and maintaining a superrotating state, all of which involve a global meridional overturning circulation. The role of nonaxisymmetric eddies is crucial, however, but the detailed mechanisms may differ between Venus, Titan, and other planets.
The presence of highly evolved igneous rocks on Venus is a controversial issue. The formations of highland terranes and pancake domes are the two principal tectonic and volcanic features which argue ...in favor of the presence of silicic igneous rocks; however, the lack of water on Venus casts doubt on whether or not granites and rhyolites can form. Data returned to Earth from the Venera 13 and 14 landers show that the surface of Venus is composed of basaltic rocks similar in composition to those found on Earth. Here it is shown that anhydrous and hydrous fractional crystallization modeling using the Venera 13 and 14 data as starting materials can produce compositions similar to terrestrial phonolites and rhyolites. It is suggested that at shallow crustal levels (i.e., ≤ 0.1 GPa), mafic magmas can differentiate into silicic magmas resembling phonolites or rhyolites which may or may not erupt. Furthermore, the hydrous equilibrium partial melting models can produce rocks similar to terrestrial andesites and rhyolites, whereas anhydrous models suggest that there may be a uniquely Venusian type of silicic rock. The silicic rocks, if present, could act as “continental nucleation” sites and/or their presence may facilitate preferential sites of shearing and deformation of the Venusian crust.
Key Points
Dry fractionation of Venusian basaltic rocks can produce silicic magmasPancake domes may be surficial expression of shallow level magma chambersConcentration of silicic rocks may form continental nucleation sites on Venus
The recently selected NASA VERITAS and DAVINCI missions, the ESA EnVision, the Roscosmos Venera-D will open a new era in the exploration of Venus. One of the key targets of the future orbiting and ...in-situ investigations of Venus is the identification of volcanically active areas on the planet. The study of the areas characterized by recent or ongoing volcano-tectonic activity can inform us on how volcanism and tectonism are currently evolving on Venus. Following this key target, the manuscript by Brossier et al. (2022) (https://doi.org/10.1029/2022GL099765) extends the successful approach and methodology used by previous works to Ganis Chasma in Atla Regio. We comment here on the main results of the manuscript published by Brossier et al. (2022) (https://doi.org/10.1029/2022GL099765) and discuss the important implications of their work for the future orbiting and in-situ investigations of Venus. Their results add further lines of evidence indicating possibly recent volcanism on Venus.
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