Tailward flow of energetic neutral atoms observed at Venus

Galli, André; Fok, M.‐C.; Würz, Peter; Barabash, S.; Grigoriev, Alexander; Futaana, Yoshifumi; Holmström, Mats; Ekenbäck, A.; Kallio, Esa; Gunell, H.

doi:10.1029/2008je003096

Cited by 22 publications

(27 citation statements)

References 24 publications

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“…These observations confirm the previous discussed discrepancies between Lyman-α and in situ observations that the exospheres of Mars and Venus are populated by various energetic hydrogen populations. The observations show that charge exchange processes between solar wind protons and neutral particles are relevant for the outer part of the planetary coronae (Futaana et al 2006a(Futaana et al , 2006bGalli et al 2006aGalli et al , 2006bGalli et al , 2008aGalli et al , 2008bGunell et al 2006).…”

Section: Ena Imaging Around Solar System Planetsmentioning

confidence: 95%

Hydrogen ENA-cloud observation and modeling as a tool to study star-exoplanet interaction

Lämmer

Kislyakova

Holmström

et al. 2011

Astrophys Space Sci

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International audienceDuring the previous years spacecraft observations of so-called Energetic Neutral Atoms (ENAs) have become an important remote-sensing technique in planetary science for analyzing the solar wind plasma flow around the upper atmospheric environments of Solar System bodies. ENAs are produced whenever solar or stellar wind protons interact via charge exchange with a neutral particle from a planetary atmosphere so that their signals constrain both, ion distributions and neutral gas densities. The observation of ENAs which have been generated due to charge exchange with stellar wind plasma have been used for the indirect mass loss and stellar wind property estimation of Sun-like stars by observing the interaction regions carved out by the collisions between stellar winds and the interstellar medium. In this work we review ENA-observations and data interpretations at Solar System planets and recent hydrogen-cloud observations in UV Lyman-α absorption around hydrogen-rich extra-solar gas giants. We discuss the production of stellar wind related hydrogen ENA-clouds around close-in exoplanets and show how a detailed analysis of attenuation spectra obtained for transiting hydrogen-rich close-in gas giants can be used for the study of the upper atmosphere structure, the planet's magnetosphere and to obtain information on stellar wind properties. Finally, we discuss how future hydrogen cloud observations around exoplanets by space observatories like the Russia-led World Space Observatory-UV (WSO-UV) together with ESAs planned PLATO mission can be used for the reconstruction of the solar wind history or the test of magnetosphere evolution hypotheses

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Section: Ena Imaging Around Solar System Planetsmentioning

confidence: 95%

Hydrogen ENA-cloud observation and modeling as a tool to study star-exoplanet interaction

Lämmer

Kislyakova

Holmström

et al. 2011

Astrophys Space Sci

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“…The Chandra observatory observed such X-rays (Dennerl 2008). Galli et al (2008) describe the use of the models to understand the ENA emissions observed on VEX in the Venus wake.…”

Section: Test Particle Modelsmentioning

confidence: 99%

Solar Wind Interaction and Impact on the Venus Atmosphere

et al. 2017

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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.

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“…Some possible mechanisms for the creation of keV energetic neutral atoms (ENAs) in the heliosphere include the charge exchange collision of solar wind alpha particles with thermal neutral atoms from the interstellar gas (McComas et al 2011;Hilchenbach et al 1998;Gruntman 1997). Another important example involves charge exchange collisions between keV solar wind ions and neutral atoms and molecules from planetary and cometary atmospheres (Krasnopolsky & Gladstone 2005), a process which has been seen on Mars and Venus (Galli et al 2006(Galli et al , 2008Futaana et al 2006;Luhmann et al 1992). For magnetized planets, interaction of the magnetospheric ions with planetary or satellite atmospheres can be considered as a regular source of energetic atoms (Lui et al 1996).…”

Section: Introductionmentioning

confidence: 99%

Energy Relaxation of Helium Atoms in Astrophysical Gases

Lewkow

Kharchenko

Zhang

2012

ApJ

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We report accurate parameters describing energy relaxation of He atoms in atomic gases, important for astrophysics and atmospheric science. Collisional energy exchange between helium atoms and atomic constituents of the interstellar gas, heliosphere, and upper planetary atmosphere has been investigated. Energy transfer rates, number of collisions required for thermalization, energy distributions of recoil atoms, and other major parameters of energy relaxation for fast He atoms in thermal H, He, and O gases have been computed in a broad interval of energies from 10 meV to 10 keV. This energy interval is important for astrophysical applications involving the energy deposition of energetic atoms and ions into atmospheres of planets and exoplanets, atmospheric evolution, and analysis of non-equilibrium processes in the interstellar gas and heliosphere. Angular-and energy-dependent cross sections, required for an accurate description of the momentum-energy transfer, are obtained using ab initio interaction potentials and quantum mechanical calculations for scattering processes. Calculation methods used include partial wave analysis for collisional energies below 2 keV and the eikonal approximation at energies higher than 100 eV, keeping a significant energy region of overlap, 0.1-2 keV, between these two methods for their mutual verification. The partial wave method and the eikonal approximation excellently match results obtained with each other as well as experimental data, providing reliable cross sections in the astrophysically important interval of energies from 10 meV to 10 keV. Analytical formulae, interpolating obtained energy-and angular-dependent cross sections, are presented to simplify potential applications of the reported database. Thermalization of fast He atoms in the interstellar gas and energy relaxation of hot He and O atoms in the upper atmosphere of Mars are considered as illustrative examples of potential applications of the new database.

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Tailward flow of energetic neutral atoms observed at Venus

Cited by 22 publications

References 24 publications

Hydrogen ENA-cloud observation and modeling as a tool to study star-exoplanet interaction

Hydrogen ENA-cloud observation and modeling as a tool to study star-exoplanet interaction

Solar Wind Interaction and Impact on the Venus Atmosphere

Energy Relaxation of Helium Atoms in Astrophysical Gases

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