On the internal structure and magnetic fields of

Zhang, C. Z.; Zhang, K.

doi:10.1007/bf00643786

Cited by 16 publications

(12 citation statements)

References 19 publications

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“…The MoI is estimated to be 0.317-0.33 for a S-free, 0.317-0.338 for a nominal and 0.32-0.351 for a S-rich composition. These ranges are somewhat larger, but compatible with previous estimates of 0.327-0.342 and 0.329-0.341 (Dumoulin et al (2017), Zhang & Zhang (1995)). Fig.…”

Section: Comparison To Previous Studiessupporting

confidence: 90%

Interior Structure Models Of Venus

Shah¹,

Helled²,

Alibert³

et al. 2021

Preprint

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Venus' mass and radius are similar to those of Earth. However, dissimilarities in atmospheric properties, geophysical activity and magnetic field generation could hint towards significant differences in the chemical composition and interior evolution of the two planets. Although various explanations for the differences between Venus and Earth have been proposed, the currently available data are insufficient to discriminate among the different solutions. Here we investigate the possible range of Venus structure models. We assume that core segregation happened as a single-stage event. The mantle composition is inferred from the core composition using a prescription for metal-silicate partitioning. We consider three different cases for the composition of Venus defined via the bulk Si and Mg content, and the core's S content. Permissible ranges for the core size, mantle and core composition as well as the normalized moment of inertia (MoI) are presented for these compositions. A solid inner core could exist for all compositions. We estimate that Venus' MoI is 0.317-0.351 and its core size 2930-4350 km for all assumed compositions. Higher MoI values correspond to more oxidizing conditions during core segregation. A determination of the abundance of FeO in Venus' mantle by future missions could further constrain its composition and internal structure. This can reveal important information on Venus' formation and evolution, and possibly, the reasons for the differences between Venus and our home planet.

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Section: Comparison To Previous Studiessupporting

confidence: 90%

Interior Structure Models Of Venus

Shah¹,

Helled²,

Alibert³

et al. 2021

Preprint

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show abstract

“…We selected a value based on the requirement that a simulation of Venus (0.815 M ⊕ and T p = 785 K) predicts no dynamo at the present time. [The slow rotation of Venus cannot be solely responsible for the absent dynamo (Zhang & Zhang 1995).] If Venus has had a stagnant lid over its entire history, then the required viscosity enhancement for the Venusian dynamo to cease by 4.5 Gyr is a factor of 6.…”

Section: Parameter Values and A Nominal Earth-mass Casementioning

confidence: 99%

Thermodynamic Limits on Magnetodynamos in Rocky Exoplanets

Gaidos

Conrad

Manga

et al. 2010

ApJ

117

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To ascertain whether magnetic dynamos operate in rocky exoplanets more massive or hotter than the Earth, we developed a parametric model of a differentiated rocky planet and its thermal evolution. Our model reproduces the established properties of Earth's interior and magnetic field at the present time. When applied to Venus, assuming that planet lacks plate tectonics and has a dehydrated mantle with an elevated viscosity, the model shows that the dynamo shuts down or never operated. Our model predicts that at a fixed planet mass, dynamo history is sensitive to core size, but not to the initial inventory of long-lived, heat-producing radionuclides. It predicts that rocky planets larger than 2.5 Earth masses will not develop inner cores because the temperature-pressure slope of the iron solidus becomes flatter than that of the core adiabat. Instead, iron "snow" will condense near or at the top of these cores, and the net transfer of latent heat upwards will suppress convection and a dynamo. More massive planets can have anemic dynamos due to core cooling, but only if they have mobile lids (plate tectonics). The lifetime of these dynamos is shorter with increasing planet mass but longer with higher surface temperature. Massive Venus-like planets with stagnant lids and more viscous mantles will lack dynamos altogether. We identify two alternative sources of magnetic fields on rocky planets: eddy currents induced in the hot or molten upper layers of planets on very short period orbits, and dynamos in the ionic conducting layers of "ocean" planets with ∼10% mass in an upper mantle of water (ice).

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“…Venus is situated 0.72 AU from the Sun and in theory resides within the Solar System's habitable zone (Byrne et al 2019). Based on the results of modelling studies, Venus is thought to have a large metallic core, broadly similar to that of Earth (Zhang and Zhang 1995). However, unlike Earth, Venus does not have a significant global magnetic field (Jacobson et al 2017).…”

Section: Planetary Parametersmentioning

confidence: 99%

What is the Oxygen Isotope Composition of Venus? The Scientific Case for Sample Return from Earth’s “Sister” Planet

Greenwood

Anand

2020

Space Sci Rev

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Venus is Earth’s closest planetary neighbour and both bodies are of similar size and mass. As a consequence, Venus is often described as Earth’s sister planet. But the two worlds have followed very different evolutionary paths, with Earth having benign surface conditions, whereas Venus has a surface temperature of 464 °C and a surface pressure of 92 bar. These inhospitable surface conditions may partially explain why there has been such a dearth of space missions to Venus in recent years. The oxygen isotope composition of Venus is currently unknown. However, this single measurement ($\Delta ^{17}\text{O}$ Δ 17 O ) would have first order implications for our understanding of how large terrestrial planets are built. Recent isotopic studies indicate that the Solar System is bimodal in composition, divided into a carbonaceous chondrite (CC) group and a non-carbonaceous (NC) group. The CC group probably originated in the outer Solar System and the NC group in the inner Solar System. Venus comprises 41% by mass of the inner Solar System compared to 50% for Earth and only 5% for Mars. Models for building large terrestrial planets, such as Earth and Venus, would be significantly improved by a determination of the $\Delta ^{17}\text{O}$ Δ 17 O composition of a returned sample from Venus. This measurement would help constrain the extent of early inner Solar System isotopic homogenisation and help to identify whether the feeding zones of the terrestrial planets were narrow or wide. Determining the $\Delta ^{17}\text{O}$ Δ 17 O composition of Venus would also have significant implications for our understanding of how the Moon formed. Recent lunar formation models invoke a high energy impact between the proto-Earth and an inner Solar System-derived impactor body, Theia. The close isotopic similarity between the Earth and Moon is explained by these models as being a consequence of high-temperature, post-impact mixing. However, if Earth and Venus proved to be isotopic clones with respect to $\Delta ^{17}\text{O}$ Δ 17 O , this would favour the classic, lower energy, giant impact scenario. We review the surface geology of Venus with the aim of identifying potential terrains that could be targeted by a robotic sample return mission. While the potentially ancient tessera terrains would be of great scientific interest, the need to minimise the influence of venusian weathering favours the sampling of young basaltic plains. In terms of a nominal sample mass, 10 g would be sufficient to undertake a full range of geochemical, isotopic and dating studies. However, it is important that additional material is collected as a legacy sample. As a consequence, a returned sample mass of at least 100 g should be recovered. Two scenarios for robotic sample return missions from Venus are presented, based on previous mission proposals. The most cost effective approach involves a “Grab and Go” strategy, either using a lander and separate orbiter, or possibly just a stand-alone lander. Sample return could also be achieved as part of a more ambitious, extended mission to study the venusian atmosphere. In both scenarios it is critical to obtain a surface atmospheric sample to define the extent of atmosphere-lithosphere oxygen isotopic disequilibrium. Surface sampling would be carried out by multiple techniques (drill, scoop, “vacuum-cleaner” device) to ensure success. Surface operations would take no longer than one hour. Analysis of returned samples would provide a firm basis for assessing similarities and differences between the evolution of Venus, Earth, Mars and smaller bodies such as Vesta. The Solar System provides an important case study in how two almost identical bodies, Earth and Venus, could have had such a divergent evolution. Finally, Venus, with its runaway greenhouse atmosphere, may provide data relevant to the understanding of similar less extreme processes on Earth. Venus is Earth’s planetary twin and deserves to be better studied and understood. In a wider context, analysis of returned samples from Venus would provide data relevant to the study of exoplanetary systems.

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On the internal structure and magnetic fields of

Cited by 16 publications

References 19 publications

Interior Structure Models Of Venus

Interior Structure Models Of Venus

Thermodynamic Limits on Magnetodynamos in Rocky Exoplanets

What is the Oxygen Isotope Composition of Venus? The Scientific Case for Sample Return from Earth’s “Sister” Planet

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