Venus Orbiter Research Articles

In situ observations of large-amplitude Alfvén waves heating and accelerating the solar wind.

After leaving the Sun's corona, the solar wind continues to accelerate and cools, but more slowly than expected for a freely expanding adiabatic gas. Alfvén waves are perturbations of the interplanetary magnetic field that transport energy. We use in situ measurements from the Parker Solar Probe and Solar Orbiter spacecraft to investigate a stream of solar wind as it traverses the inner heliosphere. The observations show heating and acceleration of the plasma between the outer edge of the corona and near the orbit of Venus, along with the presence of large-amplitude Alfvén waves. We calculate that the damping and mechanical work performed by the Alfvén waves are sufficient to power the heating and acceleration of the fast solar wind in the inner heliosphere.

Pioneer Venus Orbiter Observations of Solar Wind Driven Magnetosonic Waves Interacting With the Dayside Venusian Ionosphere

AbstractWe use in situ plasma observations made by the Pioneer Venus Orbiter spacecraft to show for the first time that magnetosonic waves can couple the solar wind to the upper ionosphere and deposit energy there. The waves are generated upstream of Venus, are advected into the shock and propagate across the draped magnetic field, through the magnetosheath and into the dayside upper ionosphere. The magnetosonic waves damp in the upper ionosphere in a region where physical collisions are rare, and electromagnetic forces must control this damping. The waves damp when the ionospheric heavy ion density is a few thousand cm−3 and wave‐particle interactions with the dominant O+ ions are postulated as the damping mechanism. Estimates of ion heating rates show that 1%–5% of the O+ ion distribution function could be heated to escape energy in 10–40 s.

The Transfer of Solar Wind Energy to the Venusian Ionosphere Through Magnetic Pumping: Evidence From Pioneer Venus Orbiter Observations

AbstractThe collisionless nature of planetary magnetospheres means that electromagnetic forces are fundamental in controlling the flow of energy and momentum through these systems. We use Pioneer Venus Orbiter (PVO) observations to demonstrate that the magnetic pumping process can be active at Venus, in analogy to its recent discovery at Mars. The presented case study demonstrates the framework for how the process can work at Venus, and the results of a statistical analysis show that the ambient plasma conditions support the process being active. Magnetic pumping enables low frequency magnetosonic waves to heat ambient ionospheric electrons and provides a mechanism that couples the solar wind to the Venusian ionosphere. This is the first time the magnetic pumping process has been discussed at Venus.

Frequency Channel Selection and Performance Simulation of a Microwave Radiometer for Temperature and Sulfuric Compound Profiling of the Venusian Lower Atmosphere

AbstractExploring the Venusian lower atmosphere is crucial for studying the atmospheric circulation, surface‐atmosphere interactions, and origin and evolution of the Venusian atmosphere and climate. In this study, we investigate the theoretical capabilities of a downward‐looking passive microwave sounder placed in low Venus orbit to measure the temperature, sulfur dioxide (SO2) and gaseous sulfuric acid (H2SO4(g)) profiles. A nonlinear iterative retrieval algorithm combining a radiative transfer (RT) model and an optimal‐estimation‐based inversion algorithm is established. With the RT model adapted to the Venusian atmosphere, simulations under different atmospheric conditions are performed to optimize the selection of frequency channels. The achievable altitude coverage, vertical resolution and corresponding expected precision of the temperature, SO2 and H2SO4(g) retrievals from the multi‐channel brightness temperature measurements are quantified via retrieval simulations. The temperature can be retrieved from the surface of Venus to an altitude of ∼61 km with a precision of 1–3.5 K and a vertical resolution of 6–15 km. A precision of 10%–35% is expected for SO2 in the ∼12–64 km altitude range and with a vertical resolution of 8–19 km. H2SO4(g) can be retrieved in the ∼36–54 km altitude range with a precision of 10%–30% and a vertical resolution of 6–13 km.

Feasibility of meteor surveying from a Venus orbiter

Meteor and bolide phenomena caused by the atmospheric ablation of incoming meteoroids are predicted to occur at the planet Venus. Their systematic observation would allow to measure and compare the sub-mm to m meteoroid flux at different locations in the solar system. Using a physical model of atmospheric ablation, we demonstrate that Venus meteors would be brighter, shorter-lived, and appear higher in the atmosphere than Earth meteors. To investigate the feasibility of meteor detection at Venus from an orbiter, we apply the SWARMS survey simulator tool to sets of plausible meteoroid population parameters, atmospheric models and instrument designs suited to the task, such as the Mini-EUSO camera operational on the ISS since 2019. We find that such instrumentation would detect meteors at Venus with a 1.5× to 2.5× higher rate than at Earth. The estimated Venus–Earth detection ratio remains insensitive to variations in the chosen observation orbit and detector characteristics, implying that a meteor survey from Venus orbit is feasible, though contingent on the availability of suitable algorithms and methods for efficient on-board processing and downlinking of the meteor data to Earth. We further show that a hypothetical camera onboard the upcoming EnVision mission to Venus similar to the ISS instrument should detect many times more meteors than needed for an initial characterisation of the large meteoroid population at 0.7 au from the Sun.

Propagation of nonlinear ion-acoustic fluctuations in the mantle of Venus

Motivated by the observations of ion-acoustic fluctuations with the Parker Solar Probe (PSP) and earlier by the Pioneer Venus Orbiter (PVO) in the Venusian magnetosheath, we investigate the nature of ion-acoustic solitary and double-layer (DL) structures in the mantle. We employed a hydrodynamic description along with reductive perturbation theory to derive the nonlinear Zakharov—Kuznetsov equation that elucidates the dynamics of three-dimensional ion-acoustic wave packets. Using the spacecraft measurements of the plasma configuration at Venus, we carried out a parametric analysis of these structures, including the influence of the magnetic field strength and the relative densities and temperatures, considering two cases: quasi-parallel and oblique propagation. Moreover, we determined the structural characteristics of these waves, where oblique (quasi-parallel) solitary waves have a potential of 0.4 V (0.4 V) and a maximum electric field amplitude Em ~ 0.024 mV m−1 (8 m V m−1) across spatial and temporal widths of ~40–80 km (~140–200 m) and 0.4 s (1.6 ms). These waves produce low-frequency electrostatic activity in the frequency range of 1.6–10 Hz (630–3160 Hz). Quasi-parallel DLs have potential drops of (6.5–13) V and Em ~ (0.16–0.35) mV m−1 with a width and duration of (100–120) m and ~1 ms, and a frequency range of ~630–3980 Hz. These outcomes can explain the detected electrostatic fluctuations above the ionosphere via PVO in the frequency channels of 730 Hz and 5.4 kHz. Furthermore, the DL features estimated in this work are in line with the recent PSP measurements of the DLs propagating in the magnetosheath of Venus.

Formation of the four terrestrial planets in the Jupiter–Saturn chaotic excitation scenario: fundamental properties and water delivery

The Jupiter–Saturn chaotic excitation (JSCE) scenario proposes that the protoplanetary disk was dynamically excited and depleted beyond ∼1–1.5 au in a few Myr, offering a new and plausible explanation for several observed properties of the inner solar system. Here, we expanded our previous work by conducting a comprehensive analysis of 37 optimal terrestrial planet systems obtained in the context of the JSCE scenario. Each optimal system harbored exactly four terrestrial planets analogs to Mercury, Venus, Earth, and Mars. We further investigated water delivery, feeding zones, and accretion history for the planet analogs, which allowed us to better constrain the water distribution in the disk. The main findings of this work are as follows: 1) the formation of four terrestrial planets with orbits and masses similar to those observed in our solar system in most of our sample, as evidenced by the dynamically colder and hotter orbits of Venus–Earth and Mercury–Mars analogs, and the high success rates of similar mutual orbital separations (∼40–85%) and mass ratios of the planets (∼70–90%) among the 37 systems; and 2) water was delivered to all terrestrial planets during their formation through the accretion of water-bearing disk objects from beyond ∼1–1.5 au. The achievement of Earth’s estimated bulk water content required the disk to contain sufficient water mass distributed within those objects initially. This requirement implies that Mercury, Venus, and Mars acquired water similar to the amount on Earth during their formation. Several of our planet analogs also matched additional constraints, such as the timing of Moon formation by a giant impact, Earth’s late accretion mass and composition, and Mars’s formation timescale.

A Secular Solar System Resonance that Disrupts the Dominant Cycle in Earth’s Orbital Eccentricity (g 2 − g 5): Implications for Astrochronology

The planets’ gravitational interaction causes rhythmic changes in Earth’s orbital parameters (also called Milanković cycles), which have powerful applications in geology and astrochronology. For instance, the primary astronomical eccentricity cycle due to the secular frequency term (g 2−g 5) (∼405 kyr in the recent past) utilized in deep-time analyses is dominated by the orbits of Venus and Jupiter, i.e., long eccentricity cycle. The widely accepted and long-held view is that (g 2−g 5) was practically stable in the past and may hence be used as a “metronome” to reconstruct accurate geologic ages and chronologies. However, using state-of-the-art integrations of the solar system, we show here that (g 2−g 5) can become unstable over long timescales, without major changes in, or destabilization of, planetary orbits. The (g 2−g 5) disruption is due to the secular resonance σ 12 = (g 1 − g 2) + (s 1 − s 2), a major contributor to solar system chaos. We demonstrate that entering/exiting the σ 12 resonance is a common phenomenon on long timescales, occurring in ∼40% of our solutions. During σ 12-resonance episodes, (g 2−g 5) is very weak or absent and Earth’s orbital eccentricity and climate-forcing spectrum are unrecognizable compared to the recent past. Our results have fundamental implications for geology and astrochronology, as well as climate forcing, because the paradigm that the long eccentricity cycle is stable, dominates Earth's orbital eccentricity spectrum, and has a period of ∼405 kyr requires revision.

Venus cloud sample return concept for astrobiology

The sulfuric acid clouds of Venus are of high scientific interest due to several intriguing observations from the past decades. These observations are not fully explained with current chemical models. Manyhypotheses have been posed to date, including the presence of complex organics or microbial life in the clouds. The possibility of life is primarily supported by the biologically benign temperatures in the cloud layers and is secondarily bolstered by several unresolved cloud-layer atmospheric chemical anomalies. Here we propose that a robust search for signs of life or life itself in the Venusian aerial environment requires a sample return of the cloud particles. We propose a Venus cloud sample return mission concept by performing key trade studies, and evaluating the requirements, feasibility, and technological needs. The baseline mission concept includes a Venus entry system, a balloon for sample collection and ascent in the clouds, a Venus Ascent Vehicle to deliver samples to orbit, a Venus orbiter, and an Earth return system. We present the concept of three critical systems that are the focus of our study: cloud sample collectors, an aerial platform, and a Venus Ascent Vehicle. We found an electrostatic fog collector for low-power, high-efficiency cloud sample capture. The most significant newly identified technology gaps for near-term focused development that we uncovered are the rapid inflation of a large 7000 m3 balloon and navigation and control of the ascent vehicle in a low-visibility and turbulent cloud environment. We discuss the various technologies of the sample return mission that need focused development and have synergies across multiple types of planetary missions.

The parts of the meteoroid stream originating in comet 109P/Swift-Tuttle crossing the orbits of Mercury, Venus, and Mars

The nucleus of comet 109P/Swift-Tuttle is the source of meteoroids which frequently impact the Earth as the well-known, most powerful meteor shower Perseids, #7. In addition, the stream splits into several other filaments corresponding to few other meteor showers. In this work, we investigated, if the meteoroids of 109P’s stream also impact the other three terrestrial planets. It appeared that there are meteor showers at Venus and Mars, two with the radiants in the northern and one in the southern ecliptic hemisphere of sky. Interestingly, the positions of the radiant areas of 109P’s showers are almost the same at all three planets, Venus, Earth, and Mars. Any shower being so active as the Perseids was predicted neither at Venus nor at Mars, however. Some meteoroids of one filament of the 109P’s stream also impacts the surface of Mercury, but the corresponding shower is predicted so low in number that it can scarcely be detected.

Properties of Mars' Dayside Low‐Altitude Induced Magnetic Field and Comparisons With Venus

AbstractMars and Venus have atmospheres but lack intrinsic dipole magnetic fields. Consequently, the solar wind interaction at each planet results in the formation of an induced magnetosphere. Our work aims to compare the low‐altitude (< 250 km) component of the induced magnetic field at Venus and Mars using observations from Pioneer Venus Orbiter and Mars Atmosphere and Volatile EvolutioN. We restrict the in‐situ data from Mars to regions of weak crustal magnetism. At Venus, it has long been known the vertical structure of the induced magnetic field profiles have recurring features that enable them to be classified as either magnetized or unmagnetized. We find the induced field profiles at Mars are more varied, lack recurring features, and are unable to be classified in the same way. The solar zenith angle dependence of the low‐altitude field strength at both planets is controlled by the shape of the magnetic pileup boundary. Also, because the ionospheric thermal pressure at Venus is often comparable to the solar wind dynamic pressure, the induced fields are weaker than required to balance the solar wind by themselves. By contrast, induced fields at Mars are stronger than required to achieve pressure balance. Lastly, we find the induced fields in the magnetized ionosphere of Venus have a weaker dependence on solar wind dynamic pressure than the induced fields at Mars. Our results point to planetary properties, such as planet‐Sun distance, having a major effect on the properties of induced fields at nonmagentized planets.

A Short Review on India’s Interplanetary Missions

India's space program has witnessed transformative achievements in interplanetary exploration, propelling the nation into the forefront of space science and technology. This comprehensive overview delves into key milestones, objectives, and outcomes of India's interplanetary missions, beginning with the trailblazing Chandrayaan-1 that altered lunar studies by detecting water traces. Mangalyaan-1's success in orbiting Mars on its maiden attempt underscored India's prowess in Martian exploration. Despite a setback in the Chandrayaan-2 lunar landing, it provided ground-breaking lunar data. The recently launched Aditya-L1 focuses on solar observation, capturing high-energy X-rays and solar disc images. Future missions, including Chandrayaan-3, Mangalyaan-2, and the Venus Orbiter Mission (Shukrayaan), exemplify India's commitment to advancing planetary exploration. These endeavours, marked by cutting-edge technology and diverse scientific objectives, highlight India's growing prominence in global space exploration and contribute significantly to humanity's understanding of the cosmos.

Baked before Breaking into Bits: Evidence for Atira-type Asteroid Splits

Current near-Earth asteroid orbital models cannot reproduce the observed populations close to the Sun. Supercatastrophic and tidal disruptions may explain the differences between theoretical models and observational data. Here, we explore the distributions of mutual nodal distances and the angular separation of perihelia of the known Atiras looking for evidence of past splittings. We find a number of pairs, trios, and one quartet of Atiras with mutual nodal distances as short as 0.001 au at the orbits of Mercury and Venus. The smallest of these highly correlated objects is 2023 WK3. Fragmentation or binary disruption may have triggered the recent formation of the unusual pair made of 594913 ’Ayló’chaxnim (2020 AV2) and 2012 VE46 with both mutual nodal distance and angular separation of perihelia in the first percentile of the distribution, making 2012 VE46 a robust candidate to being a former moon or piece of ’Ayló’chaxnim.

Influence of Solar Wind Variations on the Shapes of Venus’ Plasma Boundaries Based on Venus Express Observations

The interaction between the solar wind and Venus creates an induced magnetosphere. The regions of the induced magnetosphere are separated by plasma boundaries, where their shapes and sizes are influenced by variations in the surrounding environment. Investigations of the boundaries and their variability can help us understand the solar wind’s effect on Venus and unmagnetized planets in general. In this study, the bow shock and ion composition boundary locations are investigated using, for the first time, the full data set of plasma and magnetic field measurements by Venus Express taken during 2006–2014. The locations of the boundaries are examined with respect to upstream conditions and the solar cycle. We find, in agreement with previous studies using Pioneer Venus Orbiter measurements, that the bow shock location is mostly sensitive to the solar cycle and the dynamic pressure and that it exhibits asymmetries in the terminator plane, depending on the direction of the interplanetary magnetic field. The asymmetries are mainly attributed to the asymmetry in the pickup ion distribution and thus mass loading in the magnetosheath. The ion composition boundary on the dayside is found to decrease in altitude with increasing dynamic pressure during solar maximum (2006–2011), but shows no clear trends during solar minimum (2011–2014) conditions.

High temperature atomic oxygen testing for ESA’s Envision mission to Venus

EnVision will be ESA’s next Venus orbiter, providing a holistic view of the planet from its inner core to upper atmosphere to determine how and why Venus and Earth evolved so differently. The spacecraft will be equipped with a suite of instruments including a sounder to reveal underground layering, and spectrometers to study the atmosphere and surface. The thermal fluxes in orbit around Venus are high, the solar flux at Venus distance is twice its value on Earth (around 2600 W/m2), and the reflected sunlight flux has a similar order of magnitude due to the albedo. Besides, there will also be an aerobraking phase, when a third thermal flux, the aerothermal flux, needs to be considered, with a similar order of magnitude as the two others. These high total thermal fluxes, together with the cold instruments’ requirements and high-power dissipation make the thermal environment a design driver for the mission. The chemistry of the atmospheric environment during aerobraking needs also to be taken into account. Atomic oxygen exists in Venus atmosphere at the altitude range foreseen for aerobraking, with densities of up to 1017 oxygen atoms per cubic metres at aerobraking altitudes. Though the concentrations are small, their accumulation over up to 2000 atmospheric passes lead to total atomic oxygen fluences on the exposed spacecraft surfaces which are comparable to those encountered on typical Low Earth orbiting satellites (upwards of 1021 atomscm-2). This drives the selection of spacecraft materials on the most exposed surfaces. Whilst significant data exists about atomic oxygen erosion effects on materials for Low Earth Orbit, there is little knowledge about high temperature atomic oxygen effects on materials under environmental conditions representative of the Venus atmosphere. To analyse the potential risks for the Envision mission, and to assist the designers in selecting the best materials, an atomic oxygen test campaign is being performed in the ESA ESTEC atomic oxygen ground-based simulator (LEOX facility). The facility has been adapted so that material samples can be simultaneously exposed to atomic oxygen and high temperatures up to at least 200°C. For the test campaign, the Envision instrument teams and designers of the prospective satellite systems are providing candidate materials to be exposed. This includes a variety of materials to be utilised on the outside of the satellite such as thermal control coatings, optical materials, coatings for appendages and antennas and multi-layer insulation. The paper describes the modifications to the facility and the first results of the testing which has been performed.

Electrostatic Solitary Waves in the Venusian Ionosphere Pervaded by the Solar Wind: A Theoretical Perspective

Electrostatic solitary waves (ESWs) in the Venusian ionosphere that are impinged by the solar wind are investigated using a homogeneous, collisionless, and magnetized multicomponent plasma consisting of Venusian H+ and O+ ions, Maxwellian Venusian electrons and streaming solar wind protons, and suprathermal electrons following κ − distribution. The model supports the propagation of positive potential slow O+ and H+ ion-acoustic solitons. The evolution and properties of the solitons occurring in two sectors, viz., dawn-dusk and noon-midnight sector of the Venus ionosphere at an altitude of (200–2000) km, are studied. The theoretical model predicts positive potential solitons with amplitude ∼(0.067–56) mV, width ∼(1.7–53.21) m, and velocity ∼(1.48–8.33) km s−1. The bipolar soliton electric field has amplitude ∼(0.03–27.67) mV m−1 with time duration ∼(0.34–22) ms. These bipolar electric field pulses when Fourier transformed to the frequency domain occur as a broadband electrostatic noise, with frequency varying in the range of ∼9.78 Hz–8.77 kHz. Our results can explain the observed electrostatic waves in the frequency range of 100 Hz–5.4 kHz in the Venus ionosphere by the Pioneer Venus Orbiter mission. The model can also be relevant in explaining the recent observation of ESWs in the Venus magnetosheath by the Solar Orbiter during its first gravity assist maneuver of Venus.

Super rogue waves at Venusian ionosphere and mantle

Formation of super rogue ion-acoustic wave is suggested as a physical catalyst for the photochemical reaction to form the Venusian ionosphere and its mantle. Based on the observed data at Venus by Pioneer Venus Orbiter (PVO) and Venus Express (VEX), we constructed our models. The plasma model of the ionosphere consists of two positive ions fluid (H+andO+) and Maxwellian distributed ionospheric electrons. Whereas, the plasma mantle comprises streaming solar wind (SW) protons and Maxwellian SW electrons in addition to H+,O+ and electrons. To define precisely the existence regions and the features of super rogue waves (SRWs), we studied numerically the effect of the plasma parameters on the instability of the propagating pulses. At Venus’ ionosphere, we found that the increase of the ionospheric density ratio (nH0/nO0) enhances the energy of the SRWs. Whereas, in the mantle region, we found that the nonlinearity of the system is enhanced by the effect of the streaming SW proton, through its density and velocity, which leads to amplifying of the SRWs amplitude. Thus, the enhancement in the density of ionospheric particles and SW protons contributes to enhancing the photochemical reaction in the ionosphere and the mantle region.

Axion-sourced fireballs from supernovae

New feebly interacting particles would emerge from a supernova core with 100-MeV-range energies and produce $\gamma$-rays by subsequent decays. These would contribute to the diffuse cosmic $\gamma$-ray background or would have shown up in the Solar Maximum Mission (SMM) satellite from SN~1987A. However, we show for the example of axion-like particles (ALPs) that, even at distances beyond the progenitor star, the decay photons may not escape, and can instead form a fireball, a plasma shell with $T\lesssim 1$ MeV. Thus, existing arguments do not exclude ALPs with few 10 MeV masses and a two-photon coupling of a few $10^{-10}~{\rm GeV}^{-1}$. However, the energy would have showed up in sub-MeV photons, which were not seen from SN 1987A in the Pioneer Venus Orbiter (PVO), closing again this new window. A careful re-assessment is required for other particles that were constrained in similar ways.

In-orbit recalibration of Longwave Infrared Camera onboard Akatsuki

Akatsuki has been in operation since Venus orbit insertion-revenge 1 (VOI-R1) in December 2015 and has been making observations of Venus’ cloud-top temperature with Longwave Infrared Camera (LIR) since the start of nominal observations in April 2016. LIR was originally designed to maintain its performance for at least 4 years after the VOI originally planned in December 2010. Although the operation time of LIR has exceeded its designed lifetime as of August 2022, it is still functioning normally. The mechanical shutter plate has been kept at a normal temperature and used as a hot reference in determining the brightness temperature of objects when in the closed position. Since the observed temperature of the background deep space is merely a value representing the output for no radiation input, it should be the same in any observation. This was around 180 K just after the launch of Akatsuki in May 2010; however, it has gradually increased to approximately 200 K by February 2022. Average Venus disk temperatures also show a slight increasing trend. The increases of the background and Venus’ disk temperatures are most likely due to degradation of the sensitivity of the bolometer array used in LIR as an image sensor. These temperatures have apparently been increasing since LIR was activated in October 2016. While LIR is activated, the bolometer temperature is kept at 40 °C and a moderate baking effect may have accelerated degassing in the bolometer package, and the resulting increase of thermal conductivity or decrease of transmittance of the window contaminated by evaporated components may have degraded the sensitivity of the bolometer. A sensitivity degradation of 5% from October 2016 to February 2022 is estimated from the increasing trend of the background temperature. A correction has been made to the LIR data to keep the background temperature constant. The corrected data show no increasing trend in either the background or Venus’ disk temperature. The corrected data are open to the public as a more reliable dataset for investigating the long-term variability of thermal condition at cloud-top altitudes.Graphical

A method for constructing an interplanetary trajectory of a spacecraft to Venus using resonant orbits to ensure landing in the desired region

A problem of constructing the trajectory of a spacecraft flight to Venus within the framework of a mission including landing of a lander in a given region of the planet's surface is being considered. A new celestial mechanics related method based on the use of gravity assist maneuver near Venus is proposed to transfer the spacecraft to a heliocentric orbit resonant with the orbit of Venus, so that, at the next approach the planet, the given region of the surface becomes attainable for landing. It is shown that the best resonant orbit in terms of the cost of the characteristic velocity is an orbit with a 1:1 ratio of the period to the orbital period of Venus. A procedure for choosing one of possible resonant orbits depending on coordinates of the desired landing point on the surface and the launch date of the mission is described. An example of calculating the flight trajectory that ensures landing in the Vellamo-South region of the Venus surface at launch from the Earth in 2031 is considered.