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.
Venus's past climate evolution is uncertain. General circulation model simulations permit a habitable climate as late as ~0.7 Ga, and there is suggestive-albeit inconclusive-evidence for previous liquid water from surface geomorphology and mineralogy. However, it is unclear whether a habitable past can be reconciled with Venus's inferred atmospheric evolution. In particular, the lack of leftover atmospheric oxygen argues against recent water loss. Here, we apply a fully coupled model of Venus's atmospheric-interior-climate evolution from post-accretion magma ocean to present. The model self-co…
Near-Earth asteroid population models predict the existence of bodies located inside the orbit of Venus. Despite searches up to the end of 2019, none had been found. We report discovery and follow-up observations of (594913) 'Ayló'chaxnim, an asteroid with an orbit entirely interior to Venus. (594913) 'Ayló'chaxnim has an aphelion distance of ~0.65 au, is ~2 km in diameter and is red in colour. The detection of such a large asteroid inside the orbit of Venus is surprising given their rarity according to near-Earth asteroid population models. As the first officially numbered and named asteroid …
We are conducting a survey using twilight time on the Dark Energy Camera with the Blanco 4m telescope in Chile to look for objects interior to Earth's and Venus' orbits. To date we have discovered two rare Atira/Apohele asteroids, 2021 LJ4 and 2021 PH27, which have orbits completely interior to Earth's orbit. We also discovered one new Apollo type Near Earth Object (NEO) that crosses Earth's orbit, 2022 AP7. Two of the discoveries likely have diameters greater than 1 km. 2022 AP7 is likely the largest Potentially Hazardous Asteroid (PHA) discovered in about eight years. To date we have covered…
The Hesperos mission proposed in this paper is a mission to Venus to investigate the interior structure and the current level of activity. The main questions to be answered with this mission are whether Venus has an internal structure and composition similar to Earth and if Venus is still tectonically active. To do so the mission will consist of two elements: an orbiter to investigate the interior and changes over longer periods of time and a balloon floating at an altitude between 40 and 60km to investigate the composition of the atmosphere. The mission will start with the deployment of the b…
This work reviews the long-term evolution of the atmosphere of Venus, and modulation of its composition by interior-exterior cycling. The formation and evolution of Venus's atmosphere, leading to contemporary surface conditions, remain hotly debated topics, and involve questions that tie into many disciplines. We explore these various inter-related mechanisms which shaped the evolution of the atmosphere, starting with the volatile sources and sinks. Going from the deep interior to the top of the atmosphere, we describe volcanic outgassing, surface atmosphere interactions, and atmosphere escape…
Vatira-class near-Earth objects (NEOs) have orbits entirely interior to the orbit of Venus with aphelia $0.307<Q<0.718$ AU. Recently discovered asteroid 2020 AV$_2$ by the Zwicky Transient Facility on 4 January 2020 is the first known object on a Vatira orbit. Numerical integrations of 2020 AV$_2$'s nominal orbit show it remaining in the Vatira region for the next few hundred kyr before coupling to Venus and evolving onto an Atira orbit (NEOs entirely interior to Earth's orbit with $0.718<Q<0.983$ AU) and eventually scattering out to Earth-crossing. The numerical integrations of 9900 clones wi…
Nitrogen is the most common element in Earth's atmosphere and also appears to be present in significant amounts in the mantle. However, its long-term cycling between these two reservoirs remains poorly understood. Here a range of biotic and abiotic mechanisms are evaluated that could have caused nitrogen exchange between Earth's surface and interior over time. In the Archean, biological nitrogen fixation was likely strongly limited by nutrient and/or electron acceptor constraints. Abiotic fixation of dinitrogen becomes efficient in strongly reducing atmospheres, but only once temperatures exce…
High spectral resolution observations of Venus were obtained with the TEXES instrument at NASA's Infrared Telescope Facility. These observations focus on a CO$_2$ absorption feature at 791.4 cm$^{-1}$ as the shape of this absorption feature can be used to retrieve the vertical temperature profile in Venus' mesosphere. By scan-mapping the planet, we are able to build up three-dimensional temperature maps of Venus' atmosphere, covering one Earth-facing hemisphere and an altitude range of 60--83 km. A temperature map from February 12, 2019 clearly shows the three-dimensional structure of a planet…
Coupled atmospHere Interior modeL Intercomparison (CHILI). I. Evolutionary Modelling -- Primordial Magma Oceans of Earth and Venus
Institute of Astronomy, University of Cambridge（剑桥大学天文学研究所）；University of Washington（华盛顿大学）；Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）；Stanford University（斯坦福大学）；National Astronomical Observatory of Japan（日本国立天文台）；Laboratoire de Mathématiques de Versailles（凡尔赛数学实验室）；Université Paris Cité, Institut de physique du globe de Paris, CNRS（巴黎西岱大学，巴黎地球物理学院，法国国家科学研究中心）；University of Central Florida（中佛罗里达大学）；Johns Hopkins University（约翰斯·霍普金斯大学）；SRON Netherlands Research Organisation（荷兰研究组织SRON）；Leiden Observatory, University of Leiden（莱顿大学莱登天文台）；School of Physics, University of Bristol（布里斯托大学物理学院）；Institut für Geologische Wissenschaften, Freie Universität Berlin（柏林自由大学地质科学研究所）
Context images for Venus Express radio occultation measurements: A search for a correlation between temperature structure and UV contrasts in the clouds of Venus
Impactors of different types and sizes can produce a final crater of the same diameter on a planet under certain conditions. We derive the condition for such "isocrater impacts" from scaling laws, as well as relations that describe how the different impactors affect the interior of the target planet; these relations are also valid for impacts that are too small to affect the mantle. The analysis reveals that in a given isocrater impact, asteroidal impactors produce anomalies in the interior of smaller spatial extent than cometary or similar impactors. The differences in the interior could be u…
Longwave Infrared Camera (LIR) onboard 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 mid-latitudes 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 consi…
Study on the Venusian Atmospheric Thermal Structure: A Comparative Analysis between VEX/Akatsuki and Venus-GRAM/VCD
Space Physics Laboratory, VSSC（空间物理实验室，VSSC）；Research Centre, University of Kerala（喀拉拉大学研究中心）；Physical Research Laboratory（物理研究实验室）；Rheinisches Institut fur Umweltforschung, Freies Institut fur Planetenforschung（莱茵环境研究所，自由行星研究所）；Graduate School of Frontier Sciences, The University of Tokyo（东京大学前沿科学研究生院）；Faculty of Science, Kyoto Sangyo University（京都产业大学理学院）
Earth possesses a persistent, internally-generated magnetic field, whereas no trace of a dynamo has been detected on Venus, at present or in the past, although a high surface temperature and recent resurfacing events may have removed paleomagnetic evidence. Whether or not a terrestrial body can sustain an internally generated magnetic field by convection inside its metallic fluid core is determined in part by its initial thermodynamic state and its compositional structure, both of which are in turn set by the processes of accretion and differentiation. Here we show that the cores of Earth- and…
With the discovery of TRAPPIST-1 and its seven planets within 0.06 au, the correct treatment of tidal interactions is becoming necessary. The eccentricity, rotation, and obliquity of the planets of TRAPPIST-1 are indeed the result of tidal evolution over the lifetime of the system. Tidal interactions can also lead to tidal heating in the interior of the planets, which can then be responsible for volcanism and/or surface deformation. In the majority of studies to estimate the rotation of close-in planets or their tidal heating, the planets are considered as homogeneous bodies and their rheology…
Solid body tides provide key information on the interior structure, evolution, and origin of the planetary bodies. Our Solar system harbours a very diverse population of planetary bodies, including those composed of rock, ice, gas, or a mixture of all. While a rich arsenal of geophysical methods has been developed over several years to infer knowledge about the interior of the Earth, the inventory of tools to investigate the interiors of other Solar-system bodies remains limited. With seismic data only available for the Earth, the Moon, and Mars, geodetic measurements, including the observatio…
The Trappist-1 planets provide a unique opportunity to test the current understanding of rocky planet evolution. The James Webb Space Telescope is expected to characterize the atmospheres of these planets, potentially detecting CO$_2$, CO, H$_2$O, CH$_4$, or abiotic O$_2$ from water photodissociation and subsequent hydrogen escape. Here, we apply a coupled atmosphere-interior evolution model to the Trappist-1 planets to anticipate their modern atmospheres. This model, which has previously been validated for Earth and Venus, connects magma ocean crystallization to temperate geochemical cycling.…
Context. Findings by the Helios and STEREO mission have indicated the presence of a resonant circumsolar ring of dust associated with Venus. Attempts to model this phenomenon as an analogue to the resonant ring of Earth - as a result of migrating dust trapped in external mean-motion resonances (MMRs) - have so far been unable to reproduce the observed dust feature. Other theories of origin have recently been put forward. However, the reason for the low trapping efficiency of Venus's external MMRs remains unclear. Aims. Here we look into the nature of the dust trapping resonant phenomena that a…
Astrophysical observations reveal a large diversity of radii and masses of exoplanets. It is important to characterize the interiors of exoplanets to understand planetary diversity and further determine how unique, or not, Earth is. Assessing interior structure is challenging because there are few data and large uncertainties. Thus, for a given exoplanet a range of interior structure models can satisfy available data. Typically, interior models aim to constrain the radial structure and composition of the core and mantle, and additionally ice, ocean, and gas layer if appropriate. Constraining t…
By plotting empirical chemical element abundances on Earth relative to the Sun and normalized to silicon versus their first ionization potentials, we confirm the existence of a correlation reported earlier. To explain this, we develop a model based on principles of statistical physics that predicts differentiated relative abundances for any planetary body in a solar system as a function of its orbital distance. This simple model is successfully tested against available chemical composition data from CI chondrites and surface compositional data of Mars, Earth, the Moon, Venus, and Mercury. We s…
The gravity field of a giant planet is typically our best window into its interior structure and composition. Through comparison of a model planet's calculated gravitational potential with the observed potential, inferences can be made about interior quantities, including possible composition and the existence of a core. Necessarily, a host of assumptions go into such calculations, making every inference about a giant planet's structure strongly model dependent. In this work we present a more general picture by setting Saturn's gravity field, as measured during the \emph{Cassini} Grand Finale,…
Context. The Juno spacecraft has obtained highly accurate tidal Love numbers, which provide important constraints on the tidal response and interior structure of Jupiter. Aims. In order to exploit these observations, it is necessary to develop an approach for accurately calculating the tidal response of Jupiter for a given interior model and to investigate the role of interior structure. Methods. We directly solve the linearized tidal equations of a compressible, self-gravitating, rotating and viscous fluid body using a pseudo-spectral method. The Coriolis force is fully taken into account but…
We explore the application of machine learning based on mixture density neural networks (MDNs) to the interior characterization of low-mass exoplanets up to 25 Earth masses constrained by mass, radius, and fluid Love number $k_2$. We create a dataset of 900$\:$000 synthetic planets, consisting of an iron-rich core, a silicate mantle, a high-pressure ice shell, and a gaseous H/He envelope, to train a MDN using planetary mass and radius as inputs to the network. For this layered structure, we show that the MDN is able to infer the distribution of possible thicknesses of each planetary layer from…
In the past few years, the number of confirmed planets has grown above 2000. It is clear that they represent a diversity of structures not seen in our own solar system. In addition to very detailed interior modeling, it is valuable to have a simple analytical framework for describing planetary structures. Variational principle is a fundamental principle in physics, entailing that a physical system follows the trajectory which minimizes its action. It is alternative to the differential equation formulation of a physical system. Applying this principle to planetary interior can beautifully summa…
We examine the comparative thermal evolution of Jupiter and Saturn applying recent theoretical results for helium's immiscibility in fluid metallic hydrogen. The redistribution of helium in their interiors proceeds very differently for the two planets. We confirm that based on Jupiter's atmospheric helium depletion as observed in situ by the Galileo entry probe, Jupiter's interior helium has differentiated modestly, and we present models reconciling Jupiter's helium depletion, radius, and heat flow at the solar age. Jupiter's recently revised Bond albedo implies a lower intrinsic flux for the …
Uranus and Neptune form a distinct class of planets in our solar system. Given this fact, and ubiquity of similar-mass planets in other planetary systems, it is essential to understand their interior structure and composition. However, there are more open questions regarding these planets than answers. In this review we concentrate on the things we do not know about the interiors of Uranus and Neptune with a focus on why the planets may be different, rather than the same. We next summarize the knowledge about the planets' internal structure and evolution. Finally, we identify the topics that s…
Heavy elements, even though its smaller constituent, are crucial to understand Jupiter formation history. Interior models are used to determine the amount of heavy elements in Jupiter interior, nevertheless this range is still subject to degeneracies due to uncertainties in the equations of state. Prior to Juno mission data arrival, we present Jupiter optimized calculations exploring the effect of different model parameters in the determination of Jupiter's core and heavy element's mass. We perform comparisons between equations of state published recently. The interior model of Jupiter is calc…
Atmospheric characterization through spectroscopic analysis, an essential tool of modern exoplanet science, can benefit significantly from the context provided by interior structure models. In particular, the planet's bulk metallicity $Z_p$ places an upper limit on potential atmospheric metallicity. Here we construct interior structure models to derive $Z_p$ and atmospheric metallicity upper limits for 403 known transiting giant exoplanets. These limits are low enough that they can usefully inform atmosphere models. Additionally, we argue that comparing $Z_p$ to the observed atmospheric metall…
Water content and the internal evolution of terrestrial planets and icy bodies are closely linked. The distribution of water in planetary systems is controlled by the temperature structure in the protoplanetary disk and dynamics and migration of planetesimals and planetary embryos. This results in the formation of planetesimals and planetary embryos with a great variety of compositions, water contents and degrees of oxidation. The internal evolution and especially the formation time of planetesimals relative to the timescale of radiogenic heating by short-lived 26Al decay may govern the amount…
The giant planets were the first to form and hold the key to unveiling the solar system's formation history in their interiors and atmospheres. Furthermore, the unique conditions present in the interiors of the giant planets make them natural laboratories for exploring different elements under extreme conditions. We are at a unique time to study these planets. The missions Juno to Jupiter and Cassini to Saturn have provided invaluable information to reveal their interiors like never before, including extremely accurate gravity data, atmospheric abundances and magnetic field measurements that r…
