Interior Of Venus Research Articles

Stress state of the Mars’ and Venus’ interior

It is shown that most of the epicenters of marsquakes are located in the zones of extension and fairly large shear stresses associated with the deviation of Mars from hydrostatic equilibrium. Non-hydrostatic stresses in the interior of Venus are calculated for two types of models: an elastic model and a model with a lithosphere of varying thickness (150–500 km) overlying a weakened layer that has partially lost its elastic properties. Numerical modeling of the system of elastic equilibrium equations for a gravitating planet is carried out with a step of 1°×1° in latitude and longitude up to a depth of 480 km – the first phase transition zone in the mantle. The topography and the gravitational field of the planet are the boundary conditions of the problem. Overall, the level of nonhydrostatic stress on Venus is not very high. On the surface and in the crust, the highest shear stresses are observed in the region of the Maxwell Monte on Ishtar Terra. Beneath the Maxwell Monte, shear stresses in the crust reach 80 MPa and compressive stresses, 125–150 MPa, depending on the model. Tensile stresses around this region are about 20 MPa. The highest tensile stresses occur in the regions beneath structures such as Lavinia Planitia, Sedna Planitia, and Aino Planitia.

VALENTInE: A Concept for a New Frontiers–Class Long-duration In Situ Balloon-based Aerobot Mission to Venus

Described here is a concept for a variable-altitude aerobot mission to Venus developed as part of the 2020 NASA Planetary Science Summer School in collaboration with NASA Jet Propulsion Laboratory. The Venus Air and Land Expedition: a Novel Trailblazer for in situ Exploration (VALENTInE) is a long-duration New Frontiers–class mission to Venus in alignment with the goals recommended by the 2013 Planetary Science Decadal Survey. VALENTInE would have five science objectives: (1) determine the driving force of atmospheric superrotation, (2) determine the source of D/H and noble gas inventory, (3) determine the properties that govern how light is reflected within the lower cloud later, (4) determine whether the tesserae are felsic, and (5) determine whether there is evidence of a recent dynamo preserved in the rock record. The proposed mission concept has a total duration of 15 Earth days and would float at an altitude of 55 km, along with five dips to a lower altitude of 45 km to study Venus’s lower atmosphere. The instrument payload allows for measurements of the atmosphere, surface, and interior of Venus and includes six instruments: an atmospheric weather suite, a mass spectrometer, a multispectral imager, a near-infrared spectrometer, light detection and ranging, and a magnetometer. Principle challenges included a limitation caused by battery lifetime and low technology readiness levels for aerobots that can survive the harsh conditions of Venus’s atmosphere. This preliminary mission was designed to fit within an assumed New Frontiers 5 (based on inflated New Frontiers 4) cost cap.

Dynamics of Lithospheric Overturns and Implications for Venus's Surface

AbstractVenus is currently characterized by stagnant‐lid mantle convection, but could have previously experienced episodes of global resurfacing due to lithospheric overturn. Using numerical models of Venus's interior, we attempt to explain Venus's surface characteristics in the context of interior evolution and to understand how Venus's tectonic history has diverged from Earth's. For both the stagnant‐ and the episodic‐lid regime, we explore the role of reference mantle viscosity; for the latter regime, we also explore the role of the lithospheric yield stress. Our stagnant‐lid models predict thicker crust and younger surface than typically inferred from cratering statistics. When considering resurfacing episodes, the yield stress influences the frequency of overturns, which limits crustal thickness to better agree with previous independent estimates. Surface age is variable and depends on overturn frequency and resurfacing rate between overturns but reaches larger values just before an upcoming overturn event compared to values in the stagnant‐lid cases. Both regimes predict substantial lateral variations in surface age, instead of an end‐member uniform surface age indicating the cessation time of the last overturn, because ongoing volcanic resurfacing is spatially heterogeneous and dominates over tectonic resurfacing. Reviewing the crater‐based surface age variations suggests that the model‐predicted age spreads in the episodic scenario could be consistent with Venus's cratering record. Moreover, we find that a small fraction of crust can resist recycling during overturns. These outcomes indicate that overturn events may allow for surface age variations that reproduce Venus's surface better than stagnant‐lid models.

Inversion of Venus internal structure based on geodetic data

Understanding the internal structure of Venus promotes the exploration of the evolutionary history of this planet. However, the existing research concerning the internal structure of Venus has not used any inversion methods. In this work we employed an inversion method to determine the internal structure of Venus using observational or hypothetical geodetic data; these data include mass, mean radius, mean moment of inertia and second degree tidal Love number k2. To determine the core state of Venus, we created two models of Venus, an isotropic 3-layer model with entire liquid core and an isotropic 4-layer model with liquid outer core and a solid inner core, assuming that the interior of Venus is spherically symmetric and in hydrostatic equilibrium. A series of the sensitivity analysis of interior structure parameters to the geodetic data considered in here shows that not all of the parameters can be constrained by the geodetic data from Venus. On this basis, a Markov Chain Monte Carlo algorithm was used to determine the posterior probability distribution and the optimal values of the internal structure parameters of Venus with the geodetic data. We found that the 3-layer model is more credible than the 4-layer model via currently geodetic data. For the assumption of the 3-layer model with the k2 = 0.295 ± 0.066, I/MR2 = 0.33 ± 0.0165, and kgm−3, the liquid iron-rich core of Venus has a radius of km, which suggests a larger core than previous research has indicated. The average density of the mantle and liquid core of Venus are and kgm−3, respectively.

Electrical conductivity of tremolite under high temperature and pressure: implications for the high-conductivity anomalies in the Earth and Venus

We measured the electrical conductivity of tremolite over a range of pressures (1.0, 1.5, and 2.0 GPa) and temperatures (648–1373 K). At temperatures lower than 1173 K, the electrical conductivity of tremolite was ~ 0.001 S/m, but once the dehydroxylation reaction took place at 1173 K, we observed a significant increase in the electrical conductivity. The electrical conductivity continued to increase until it reached its maximum value of ~ 1 S/m at a temperature of 1373 K, which we attributed to dehydroxylation in the tremolite samples. The electrical behavior was altered by the physical breakdown of the tremolite structure, rather than the oxidation process. The decomposition of tremolite resulted in the creation of diopside, enstatite, and quartz. To explain some anomalous conductivity measurements, we propose that iron-free amphibole experiences a dehydroxylation mechanism that differs from the dehydroxylation mechanism observed in iron-bearing amphiboles. Our conductivity analyses indicate that the observed increase in the electrical conductivity in deep subduction regions (at depths of ~ 180 km) is driven by the dehydroxylation of tremolite and by the mixing of lherzolite and tremolite in the upper mantle. Using our data and previously published temperature gradient data, we were able to extrapolate reasonable electrical conductivity values for the surface and interior of Venus.

Tidal constraints on the interior of Venus

AbstractAs a prospective study for a future exploration of Venus, we compute the tidal response of Venus' interior assuming various mantle compositions and temperature profiles representative of different scenarios of Venus' formation and evolution. The mantle density and seismic velocities are modeled from thermodynamical equilibria of mantle minerals and used to predict the moment of inertia, Love numbers, and tide‐induced phase lag characterizing the signature of the internal structure in the gravity field. The viscoelasticity of the mantle is parameterized using an Andrade rheology. From the models considered here, the moment of inertia lies in the range of 0.327 to 0.342, corresponding to a core radius of 2900 to 3450 km. Viscoelasticity of the mantle strongly increases the potential Love number relative to previously published elastic models. Due to the anelasticity effects, we show that the possibility of a completely solid metal core inside Venus cannot be ruled out based on the available estimate of k2 from the Magellan mission (Konopliv and Yoder, 1996). A Love number k2 lower than 0.27 would indicate the presence of a fully solid iron core, while for larger values, solutions with an entirely or partially liquid core are possible. Precise determination of the Love numbers, k2 and h2, together with an estimate of the tidal phase lag, are required to determine the state and size of the core, as well as the composition and viscosity of the mantle.

Studying lower crustal flow beneath Mead basin: Implications for the thermal history and rheology of Venus

Mead, the largest crater on Venus, has low topographic relief at the surface and at the crust-mantle boundary. Due to high surface temperatures, viscous deformation could play an important role in crustal structure. Using the finite element method, we simulate the long-term viscoelastic deformation of Mead crater and investigate the role of lower crustal flow in the evolution of the surface and subsurface topography. We examine the thermal states that allow this evolution to occur and determine the background heat flux. Our study constrains the background heat flux in the vicinity of Mead basin to 55–90mWm−2. This surface heat flow is generally higher than the average Venusian global values suggested by recent thermal models. In addition by applying hydrous and anhydrous creep rheological parameters, we demonstrate that the Venus's interior is rheologically dry and that the crust near Mead could be relatively high in plagioclase.

Did a mega-collision dry Venus' interior?

The limited relaxation of shapes of impact craters and high correlation between topography and gravity are some of the reasons that support the widely accepted view that the interior of Venus is dry compared to Earth. The fact that the atmospheric abundance of 40Ar is only ~ 25% of the radiogenic gas produced inside Venus argues that Venus is not thoroughly degassed and its interior has not been dried over time. Therefore Venus must have lost its water very early in its history, before any significant 40Ar was produced. Current ideas suggest that Venus did not suffer a major impact. Therefore one would not expect it to have been substantially molten. As a result degassing all its water would be difficult and losing all the water without leaving oxygen in the atmosphere would also be very difficult. To overcome the above difficulties in explaining a dry Venus interior, a new hypothesis is proposed that Venus formed by a near head-on collision of two large planetary embryos, as might be expected from favoured oligarchic planetary accretion. Such a collision would be sufficiently large to melt totally and briefly vapourise a significant proportion of both bodies. This would allow much of the released water to react rapidly with iron. Depending upon the reaction hydrogen is either expected to escape to space or enter the core. Oxygen would form FeO, most of which would enter the core, together with other iron reaction products. Most everything else not caught in the hydrodynamic escape driven by any hydrogen stream would be gravitationally retained by the final body. The model can therefore reconcile the 40Ar data, a virtually oxygen free atmosphere and a dry interior. An appropriate large collision also provides an easy explanation for the retrograde rotation of Venus. The possible implications for inner core and magnetic field formation; and atmosphere evolution including effects on D/H, C, N and inert gases are also discussed. A simple test of this hypothesis is that, in contrast to the current Venus paradigm, little or no hydrated minerals should be found on the surface.

Effects of crustal heterogeneity on the morphology of chasmata, Venus

The Ix‐Chel, Kuanja, and Vir‐ava Chasmata (IKVC) are a 7000‐km‐long collection of discontinuous topographic troughs and deformation suites. Collectively, they account for approximately 12.5% of the ∼55,000 linear km of chasmata on Venus; however, morphologically the IKVC differs significantly from the majority (75%) of Venusian chasmata because it lacks corona features. Coronae represent notable volumes of material both erupted onto the surface and intruded into the crust. Together with chasmata, coronae may also be important indicators of Venus's interior convective processes as well as significant contributors to Venus's heat loss. Although IKVC lacks coronae, detailed geologic and structural mapping along its length highlights previously unrecognized structural and volcanic relationships indicative of local uplift, collapse, and volcanism we call pseudocoronae. In light of this mapping, previous corona formation models (theoretical and numerical) are evaluated, and an amended hypothesis (diapir stagnation) is presented for pseudocorona formation. The diapir stagnation model proposes that variations of the crustal thickness perturb corona formation and thus affect their resultant surface morphology. Chasmata are accompanied by corona development when forming in regions of relatively thin, or normal (plains‐type), crust (<20 km) but lack corona features when influenced by crustal heterogeneities (mechanical and chemical) at depth associated with thick crustal plateau roots (35–80 km (e.g., Ovda, Thetis, and Phoebe Regios)). Beneath crustal plateaus, diapiric rise is inhibited by (1) the presence of a low‐density crustal keel that creates a deep‐seated density trap and (2) a composition‐dependent mechanically weak crust‐mantle boundary layer. Diapir stagnation can be characterized or accompanied by minimal broad doming of the surface, formation of radial and concentric extension structures, lateral dike propagation, and collapse, all of which may be accompanied by limited volume surface eruptions of the lowest density melt phases. Through time, the crust‐mantle boundary layer may repeatedly lift and subside through conductive heating and viscous flow, which may allow more voluminous melt migration and eruption; however, true coronae fail to develop.

Stagnant lid convection on Venus

The effect of strongly temperature‐dependent viscosity on convection in the interior of Venus is studied systematically with the help of finite element numerical models. For viscosity contrasts satisfying experimental constraints on the rheology of rocks, Venus is likely to be in the regime of stagnant lid convection. This regime is characterized by the formation of a slowly creeping, very viscous lid on top of the mantle‐Venusian lithosphere and is in agreement with the tectonic style observed on Venus. Stagnant lid convection explains large geoid to topography ratios on Venus by the thermal thinning of a thick lithosphere. The thickness of the lithosphere can be as large as 400–550 km for Beta Regio and 200–400 km on average. Geoid and topography data and experimental data on the rheology of rocks provide constraints on the viscosity of the mantle, 1020–1021 Pa s; the convective stresses in the interior, 0.2–0.5 MPa; the stresses in the lid, 100–200 MPa; the velocity in the interior, 0.5–3 cm yr−1; and the heat flux beneath the lithosphere, 8–16 mW m−2. Parameterized convection calculations of thermal history of Venus are difficult to reconcile with a thick present‐day lithosphere. However, a sufficiently thick lithosphere can be formed if a convective regime with mobile plates was replaced by stagnant lid convection around 0.5 b.y. ago. One of the possible explanations for the cessation of Venusian late tectonics is that during the evolution of Venus, stresses in the lid dropped below the yield strength of the lithosphere. This model predicts a drastic drop in the heat flux, thickening of the lithosphere, and suppression of melting and is consistent with the hypothesis of cessation of resurfacing on Venus around 0.5 b.y. ago.

10. The surface and interior of venus

Present ideas about the surface and interior of Venus are based on data obtained from (1) Earth-based radio and radar: temperature, rotation, shape, and topography; (2) fly-by and orbiting spacecraft: gravity and magnetic fields; and (3) landers: winds, local structure, gamma radiation. Surface features, including large basins, crater-like depressions, and a linear valley, have been recognized from recent ground-based radar images. Pictures of the surface acquired by the USSR's Venera 9 and 10 show abundant boulders and apparent wind erosion.