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Venus has intrigued planetary scientists for decades because of its huge contrasts to Earth, in spite of its nickname of “Earth’s Twin”. Its invisible upper atmosphere and space environment are also part of the larger story of Venus and its evolution. In 60s to 70s, several missions (Venera and Mariner series) explored Venus-solar wind interaction regions. They identified the basic structure of the near-Venus space environment, for example, existence of the bow shock, magnetotail, ionosphere, as well as the lack of the intrinsic magnetic field. A huge leap in knowledge about the solar wind interaction with Venus was made possible by the 14-year long mission, Pioneer Venus Orbiter (PVO), launched in 1978. More recently, ESA’s probe, Venus Express (VEX), was inserted into orbit in 2006, operated for 8 years. Owing to its different orbit from that of PVO, VEX made unique measurements in the polar and terminator regions, and probed the near-Venus tail for the first time. The near-tail hosts dynamic processes that lead to plasma energization. These processes in turn lead to the loss of ionospheric ions to space, slowly eroding the Venusian atmosphere. VEX carried an ion spectrometer with a moderate mass-separation capability and the observed ratio of the escaping hydrogen and oxygen ions in the wake indicates the stoichiometric loss of water from Venus. The structure and dynamics of the induced magnetosphere depends on the prevailing solar wind conditions. VEX studied the response of the magnetospheric system on different time scales. A plethora of waves was identified by the magnetometer on VEX; some of them were not previously observed by PVO. Proton cyclotron waves were seen far upstream of the bow shock, mirror mode waves were observed in magnetosheath and whistler mode waves, possibly generated by lightning discharges were frequently seen. VEX also encouraged renewed numerical modeling efforts, including fluid-type of models and particle-fluid hybrid type of models, describing the plasma interaction on scales ranging from ion gyro radius to the entire induced magnetosphere. In this review article, we review what has been found from space physics measurements around Venus (from the solar wind down to the ionopause), with a particular emphasis on updated results since the Venus Express mission. We conclude the article by a short discussion on the remaining open scientific questions and the future of this field.

Various types of auroral emissions have been observed at (partially) magnetized planets (e.g., Earth, Jupiter, and Mars). Auroral emissions have also been observed at Venus, an unmagnetized planet, by the Pioneer Venus Orbiter (PVO) and ground‐based telescopes. By applying a linear relation, this study predicts the possible CO Cameron‐band emission brightness at Venus using electron observations from Venus Express (VEx). Our results suggest that to produce the PVO observations, electron acceleration is not required as in the case of discrete aurorae at magnetized planets; rather, the magnetic access of precipitating electrons to the lower atmosphere is the more limiting factor for auroral occurrence. This study helps better understand how aurorae can occur at an unmagnetized planet, in contrast to magnetized planets. It also has implications for future Venus mission design: auroral imaging can serve as a remote sensing tool to characterize the magnetization state of the Venus nightside atmosphere. Plain Language Summary Auroral emissions have been observed (partially) magnetized planets, such as Earth, Jupiter, and Mars, illuminating the plasma processes mostly related to planetary intrinsic fields. Aurorae have also been reported to occur at Venus, an unmagnetized planet, by the Pioneer Venus Orbiter (PVO). Previous modeling efforts suggest that the observed CO Cameron‐band auroral emissions are mainly produced by electrons at 10–100s of electron volts (eV) impacting the Venus nightside upper atmosphere. Yet, little was discussed in previous studies regarding how these source electrons access the atmosphere. By applying a linear relation, this study predicts the possible CO Cameron‐band emission brightness at Venus using electron observations from Venus Express (VEx). Our results suggest that to produce the PVO observations, electron acceleration is not required as in the case of discrete aurorae at magnetized planets; rather, the magnetic access of precipitating electrons to the lower atmosphere is the more limiting factor for auroral occurrence. This study helps better understand how aurorae can occur at an unmagnetized planet, in contrast to magnetized planets. It also has implications for future Venus mission design: auroral imaging can serve as a remote sensing tool to characterize the magnetization state of the Venus nightside atmosphere. Key Points We predict the possible CO Cameron‐band emission brightness at Venus using VEx electron observations by applying an empirical relationship To reproduce PVO observations, electron acceleration is not needed, but magnetic topology limits the occurrence of aurorae at Venus Auroral imaging at Venus can serve as remote sensing of the magnetic state of the Venus nightside ionosphere and magnetosphere

This study investigates the potential impact of Solar Energetic Particles (SEPs) on the V0 layer of the Venus ionosphere. Electron density profiles obtained from radio occultation experiments conducted by the Venus Express (VEX) and Akatsuki missions were utilized for this purpose. Background data from the Analyzer of Space Plasma and EneRgetic Atoms (ASPERA‐4) aboard VEX were used to detect SEP events. Additionally, observations from the Space Environment Monitor (SEM) suite onboard the Geostationary Operational Environmental Satellite (GOES) during alignments of Venus, Earth, and the Sun were also considered. Our findings indicate that while SEPs may contribute to the formation of the V0 layer, they are not the main driving force in the Venusian ionosphere. Plain Language Summary The Venusian ionosphere shows sporadic enhancements in electron density around 110 km altitude. Despite extensive investigation, the exact cause of its sporadic presence remains elusive. Previous studies have explored various theories, including meteoric influences, gravity waves, and the impact of minor atmospheric constituents such as NO, O2, C, Ar, H2, and H. However, none have conclusively explained its formation mechanism. In this study, we have investigated the potential influence of Solar Energetic Particles (SEPs) on the V0 layer. By analyzing electron density profiles obtained from VEX/Akatsuki missions, hot plasma measurements by ASPERA‐4 onboard VEX, and SEM suite onboard GOES to identify SEP events, we surmise that while SEPs may contribute to the formation of the V0 layer, they are not the primary driving force in the Venusian ionosphere. Key Points The Impact of solar energetic particle (SEP) events on the formation of V0 layers in the Venusian ionosphere has been explored Enhanced ionization is seen above the V2 layer peak whenever a V0 layer seen in the Venus ionosphere SEPs and enhanced ionization at 110 km altitudes, however, are not correlated

In this work, plasma and magnetic field data from Venus Express (VEX) were analyzed through the entire mission span (2006-2014) in order to statistically study wave mode occurrence around Venus considering different solar wind conditions. The wave mode occurrence distribution in terms of solar activity (maxima and minimum periods), solar wind pressure, and interplanetary magnetic field (IMF) east-west component orientation ( B y > 0 and B y < 0 ) were computed. Our results reveal that mirror mode occurrence does not seems to be affected by changes in the analyzed parameters. The most significant influence was observed in the Alfvén mode by the solar wind dynamic pressure, which has its occurrence rate clearly increased, during periods of high solar wind dynamic pressure. The fast mode seems to be influenced by the three analyzed parameters and tends to occur more often during periods of positive IMF B y and high solar activity. Further, a higher occurrence of fast wave mode during enhanced dynamic pressure was observed, which may be related to KH instability.

We statistically investigate the spectral scalings of magnetic fluctuations at the upstream and downstream regions near the Venusian bow shock and perform a differentiation by shock geometry. Based on the Venus Express data, 115 quasi-parallel (Q‖) bow shock crossings and 303 quasi-perpendicular (Q⊥) bow shock crossings are selected. The statistical results suggest that the bow shock tends to modify the upstream spectra flatter to 1/f noise in the magnetohydrodynamics (MHD) regime and steeper to turbulence in the kinetic regime after the magnetic fluctuations crossing the bow shock, and this modification for the Q‖ and Q⊥ bow shocks is basically consistent. However, the upstream spectral scalings are associated with the shock geometry. The changes of the spectral scalings of magnetic fluctuations near the Q‖ bow shocks are not as significant as near the Q⊥ bow shock crossings. That might result from the fluctuations generated by the backstreaming ions which can escape across the Q‖ bow shock into the foreshock. Our results suggest that the energy cascade and dissipation near Venus can be modified by the Venusian bow shock, and the Q‖ bow shock plays an important role on the energy injection and dissipation in the solar wind interaction with Venus. The large dispersion of spectral scalings indicates that this fluctuation environment is complicated, and the shock geometry is not the only key factor in the fluctuations across the Venusian bow shock. Other possible factors in the shock modification to the upstream fluctuations will be explored in future.

More than three decades have passed since the publication of the last review of the Venus clouds and hazes. The paper published in 1983 in the Venus book summarized the discoveries and findings of the US Pioneer Venus and a series of Soviet Venera spacecraft (Esposito et al. in Venus, p. 484, 1983 ). Due to the emphasis on in-situ investigations from descent probes, those missions established the basic features of the Venus cloud system, its vertical structure, composition and microphysical properties. Since then, significant progress in understanding of the Venus clouds has been achieved due to exploitation of new observation techniques onboard Galileo and Messenger flyby spacecraft and Venus Express and Akatsuki orbiters. They included detailed investigation of the mesospheric hazes in solar and stellar occultation geometry applied in the broad spectral range from UV to thermal IR. Imaging spectroscopy in the near-IR transparency “windows” on the night side opened a new and very effective way of sounding the deep atmosphere. This technique together with near-simultaneous UV imaging enabled comprehensive study of the cloud morphology from the cloud top to its deep layers. Venus Express operated from April 2006 until December 2014 and provided a continuous data set characterizing Venus clouds and hazes over a time span of almost 14 Venus years thus enabling a detailed study of temporal and spatial variability. The polar orbit of Venus Express allowed complete latitudinal coverage. These studies are being complemented by JAXA Akatsuki orbiter that began observations in May 2016. This paper reviews the current status of our knowledge of the Venus cloud system focusing mainly on the results acquired after the Venera, Pioneer Venus and Vega missions.

This is a review of current knowledge about Earth’s nearest planetary neighbour and near twin, Venus. Such knowledge has recently been extended by the European Venus Express and the Japanese Akatsuki spacecraft in orbit around the planet; these missions and their achievements are concisely described in the first part of the review, along with a summary of previous Venus observations. The scientific discussions which follow are divided into three main sections: on the surface and interior; the atmosphere and climate; and the thermosphere, exosphere and magnetosphere. These reports are intended to provide an overview for the general reader, and also an introduction to the more detailed topical surveys in the following articles in this issue, where full references to original material may be found.

This paper deals with the composition and chemical processes occurring in the neutral atmosphere of Venus. Since the last synthesis, observers as well as modellers have emphasised the spatial and temporal variability of minor species, going beyond a static and uniform picture that may have prevailed in the past. The outline of this paper acknowledges this situation and follows closely the different dimensions along which variability in composition can be observed: vertical, latitudinal, longitudinal, temporal. The strong differences between the atmosphere below and above the cloud layers also dictate the structure of this paper. Observational constraints, obtained from both Earth and Venus Express , as well as 1D, 2D and 3D models results obtained since 1997 are also extensively referred and commented by the authors. An non-exhaustive list of topics included follows: modelled and observed latitudinal and vertical profiles of CO and OCS below the clouds of Venus; vertical profiles of CO and SO 2 above the clouds as observed by solar occultation and modelled; temporal and spatial variability of sulphur oxides above the clouds. As a conclusion, open questions and topics of interest for further studies are discussed.

New observations from the Venus Express spacecraft as well as theoretical and experimental investigation of Venus analogue materials have advanced our understanding of the petrology of Venus melts and the mineralogy of rocks on the surface. The VIRTIS instrument aboard Venus Express provided a map of the southern hemisphere of Venus at ∼1 μm allowing, for the first time, the definition of surface units in terms of their 1 μm emissivity and derived mineralogy. Tessera terrain has lower emissivity than the presumably basaltic plains, consistent with a more silica-rich or felsic mineralogy. Thermodynamic modeling and experimental production of melts with Venera and Vega starting compositions predict derivative melts that range from mafic to felsic. Large volumes of felsic melts require water and may link the formation of tesserae to the presence of a Venus ocean. Low emissivity rocks may also be produced by atmosphere-surface weathering reactions unlike those seen presently. High 1 μm emissivity values correlate to stratigraphically recent flows and have been used with theoretical and experimental predictions of basalt weathering to identify regions of recent volcanism. The timescale of this volcanism is currently constrained by the weathering of magnetite (higher emissivity) in fresh basalts to hematite (lower emissivity) in Venus’ oxidizing environment. Recent volcanism is corroborated by transient thermal anomalies identified by the VMC instrument aboard Venus Express. The interpretation of all emissivity data depends critically on understanding the composition of surface materials, kinetics of rock weathering and their measurement under Venus conditions. Extended theoretical studies, continued analysis of earlier spacecraft results, new atmospheric data, and measurements of mineral stability under Venus conditions have improved our understanding atmosphere-surface interactions. The calcite-wollastonite CO 2 buffer has been discounted due, among other things, to the rarity of wollastonite and instability of carbonate at the Venus surface. Sulfur in the Venus atmosphere has been shown experimentally to react with Ca in surface minerals to produce anhydrite. The extent of this SO 2 buffer is constrained by the Ca content of surface rocks and sulfur content of the atmosphere, both of which are likely variable, perhaps due to active volcanism. Experimental work on a range of semiconductor and ferroelectric minerals is placing constraints on the cause(s) of Venus’ anomalously radar bright highlands.

Surface mineralogy records the primary composition, climate history and the geochemical cycling between the surface and atmosphere. We have not yet directly measured mineralogy on the Venus surface in situ, but a variety of independent investigations yield a basic understanding of surface composition and weathering reactions in the present era where rocks react under a supercritical atmosphere dominated by CO 2 , N 2 and SO 2 at ∼460 °C and 92 bars. The primary composition of the volcanic plains that cover ∼80% of the surface is inferred to be basaltic, as measured by the 7 Venera and Vega landers and consistent with morphology. These landers also recorded elevated SO 3 values, low rock densities and spectral signatures of hematite consistent with chemical weathering under an oxidizing environment. Thermodynamic modeling and laboratory experiments under present day atmospheric conditions predict and demonstrate reactions where Fe, Ca, Na in rocks react primarily with S species to form sulfates, sulfides and oxides. Variations in surface emissivity at ∼1 μm detected by the VIRTIS instrument on the Venus Express orbiter are spatially correlated to geologic terrains. Laboratory measurements of the near-infrared (NIR) emissivity of geologic materials at Venus surface temperatures confirms theoretical predictions that 1 μm emissivity is directly related to Fe 2+ content in minerals. These data reveal regions of high emissivity that may indicate unweathered and recently erupted basalts and low emissivity associated with tessera terrain that may indicate felsic materials formed during a more clement era. Magellan radar emissivity also constrain mineralogy as this parameter is inversely related to the type and volume of high dielectric minerals, likely to have formed due to surface/atmosphere reactions. The observation of both viscous and low viscosity volcanic flows in Magellan images may also be related to composition. The global NIR emissivity and high-resolution radar and topography collected by the VERITAS, EnVision and DAVINCI missions will provide a revolutionary advancement of these methods and our understanding of Venus mineralogy. Critically, these datasets must be supported with both laboratory experiments to constrain the style and rate weathering reactions and laboratory measurements of their NIR emissivity and radar characteristics at Venus conditions.