Ionospheric photoelectrons at Venus: Initial observations by ASPERA-4 ELS

Coates, A. J.; Frahm, R. A.; Linder, Dietmar; Kataria, D. O.; Soobiah, Y.; Collinson, G.; Sharber, J. R.; Winningham, J. D.; Jeffers, S. J.; Barabash, S.; Sauvaud, J. A.; Lundin, R.; Holmström, M.; Futaana, Yoshifumi; Yamauchi, M.; Grigoriev, Alexander; Andersson, H.; Gunell, H.; Fedorov, A.; Thocaven, J. J.; Zhang, T. L.; Baumjohann, W.; Kallio, Esa; Koskinen, H.; Kozyra, J. U.; Liemohn, Michael W.; Ma, Y.; Galli, André; Würz, Peter; Bochsler, P.; Brain, David; Roelof, E. C.; Brandt, P. C.; Krupp, N.; Woch, J.; Fräenz, M.; Dubinin, E.; McKenna‐Lawlor, S.; Orsini, S.; Cerulli-Irelli, R.; Mura, A.; Milillo, A.; Maggi, M.; Curtis, C. C.; Sandel, B. R.; Hsieh, K. C.; Szegö, K.; Asamura, A.; Grandé, M.

doi:10.1016/j.pss.2007.12.008

Cited by 50 publications

(74 citation statements)

References 18 publications

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“…These disappear once the spacecraft departs the sunlit ionosphere at $15:30. Similar photoelectron populations have been observed in Saturn's ring ionosphere [Coates et al, 2005], at Mars [Frahm et al, 2006], at Venus [Coates et al, 2007b], and at Earth [e.g., Coates et al, 1985].…”

supporting

confidence: 72%

Discovery of heavy negative ions in Titan's ionosphere

Coates

Crary

Lewis

et al. 2007

Geophysical Research Letters

386

374

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Titan's ionosphere contains a rich positive ion population including organic molecules. Here, using CAPS electron spectrometer data from sixteen Titan encounters, we reveal the existence of negative ions. These ions, with densities up to ∼100 cm−3, are in mass groups of 10–30, 30–50, 50–80, 80–110, 110–200 and 200+ amu/charge. During one low encounter, negative ions with mass per charge as high as 10,000 amu/q are seen. Due to their unexpectedly high densities at ∼950 km altitude, these negative ions must play a key role in the ion chemistry and they may be important in the formation of organic‐rich aerosols (tholins) eventually falling to the surface.

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supporting

confidence: 72%

Discovery of heavy negative ions in Titan's ionosphere

Coates

Crary

Lewis

et al. 2007

Geophysical Research Letters

386

374

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“…[11] The input parameters of the kinetic model are chosen to be consistent with the ephemeris and VEx trajectory information on 18 May 2006 [Coates et al, 2008], as shown in Figure 2 (left). The TIMED/SEE spectrum averaged over the same day is used, corresponding to a solar index of F10.7 = 73.…”

Section: Model Description and Input Parametersmentioning

confidence: 99%

“…We assess in detail the interpretation of the spectral features in the observed suprathermal electron intensity, and identify regions of the Venus ionosphere where transport of the suprathermal electrons becomes important. The clear identification of the suprathermal electron peaks also provides an estimate of the VEx spacecraft potential [Coates et al, 2008].…”

Section: Introductionmentioning

confidence: 97%

“…More recently, the suprathermal electron intensity on Venus has been acquired from measurements made with the Electron Spectrometer (ELS) of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-4) onboard Venus Express (VEx) [Barabash et al, 2007]. With a higher-energy resolution of DE/E ∼ 7% than that of the PVO RPA, distinct spectral peaks have been identified, and suggested as signatures of atomic O ionization (instead of CO 2 ) by solar HeII 30.4 nm photons at altitudes where vertical transport is expected to be important [Coates et al, 2008]. However, such a postulation needs to be justified by a detailed model-data comparison.…”

Section: Introductionmentioning

confidence: 99%

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Suprathermal electron spectra in the Venus ionosphere

et al. 2011

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[1] In this study, a multistream kinetic model is used to derive the suprathermal electron intensity in the Venus ionosphere, to be compared with the observations made by the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-4) Electron Spectrometer (ELS) instrument onboard Venus Express (VEx) on 18 May 2006. Input parameters of the model are chosen to be consistent with the detailed ephemeris information. We consider two cases for the magnetic field line configuration. The first assumes vertical magnetic field lines, while in the second the configuration is consistent with the VEx Magnetometer (MAG) measurements for that particular orbit. The model calculations suggest that the energy spectrum of suprathermal electrons not only depends on the local photoelectron production but is also strongly influenced by transport as well as energy degradation. We confirm the postulation of Coates et al. (2008) (2008). The model results indicate that the condition of local equilibrium is satisfied for suprathermal electrons below ∼155 km on Venus. However, transport becomes effective at higher altitudes, significantly altering the secondary electron production rate and leading to strongly anisotropic suprathermal electron flow. For the case with the MAG-derived, slanted magnetic field configuration, we make a data-model comparison in terms of both the absolute magnitude of the suprathermal electron intensity and the appearance of spectral peaks. The comparison suggests that the actual magnetic field lines are probably inclined more vertically than a simple extrapolation from the MAG measurements.

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“…Photoelectrons, and suprathermal electrons in general, have also been measured in the upper atmospheres of other planets and satellites including the Earth, Venus, Titan, Enceladus, and comets [e.g., Lee et al, 1980;Coates et al, 2008Coates et al, , 2011Richard et al, 2011;Ozak et al, 2012]. At all these bodies, photoelectrons are an important indicator of solar energy input into the upper atmosphere and have also provided information on the magnetic topology.…”

Section: Introductionmentioning

confidence: 99%

Model insights into energetic photoelectrons measured at Mars by MAVEN

Sakai

Rahmati

Mitchell

et al. 2015

Geophysical Research Letters

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Photoelectrons are important for heating, ionization, and airglow production in planetary atmospheres. Measured electron fluxes provide insight into the sources and sinks of energy in the Martian upper atmosphere. The Solar Wind Electron Analyzer instrument on board the MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft measured photoelectrons including Auger electrons with 500 eV energies. A two‐stream electron transport code was used to interpret the observations, including Auger electrons associated with K shell ionization of carbon, oxygen, and nitrogen. It explains the processes that control the photoelectron spectrum, such as the solar irradiance at different wavelengths, external electron fluxes from the Martian magnetosheath or tail, and the structure of the upper atmosphere (e.g., the thermal electron density). Our understanding of the complex processes related to the conversion of solar irradiances to thermal energy in the Martian ionosphere will be advanced by model comparisons with measurements of suprathermal electrons by MAVEN.

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Ionospheric photoelectrons at Venus: Initial observations by ASPERA-4 ELS

Cited by 50 publications

References 18 publications

Discovery of heavy negative ions in Titan's ionosphere

Discovery of heavy negative ions in Titan's ionosphere

Suprathermal electron spectra in the Venus ionosphere

Model insights into energetic photoelectrons measured at Mars by MAVEN

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