Observation of the Venus mantle, the boundary region between solar wind and ionosphere

Spenner, K.; Knudsen, W. C.; Miller, K. L.; Novák, V.; Russell, C. T.; Elphic, R. C.

doi:10.1029/ja085ia13p07655

Cited by 104 publications

(55 citation statements)

References 24 publications

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“…The MPB is a region in the post-shock solar wind flow around an obstacle that was originally identified at comets in the Giotto flyby of comet Halley [Neubauer et al, 1986;Mazelie et al, 1989]. It is analogous to the plasma mantle identified by Pioneer Venus in situ measurements at Venus [Spenner et al, 1980]. As we show in this letter, MGS provides a unique perspective on this boundary at Mars.…”

Section: Introductionmentioning

confidence: 75%

Evidence of electron impact ionization in the magnetic pileup boundary of Mars

Crider

Cloutier

Law

et al. 2000

Geophysical Research Letters

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Abstract. A sharp decline in electron fluxes is observed in the Mars Global Surveyor Electron Reflectometer data in conjunction with the magnetic pileup boundary. We examine the characteristics of the evolution of the electron distribution function for one orbit. We determine that the spectra can best be explained by electron impact ionization of oxygen and hydrogen. To reproduce the observed spectral evolution, we construct a model of the effects of electron impact ionization on the electron distribution function as a flow element encounters the neutral atmosphere. Using the observed post-shock electron distribution function, we are able to reproduce the observed flux attenuation. We conclude that electron impact ionization is the physical mechanism responsible for the spectral feature.

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Section: Introductionmentioning

confidence: 75%

Evidence of electron impact ionization in the magnetic pileup boundary of Mars

Crider

Cloutier

Law

et al. 2000

Geophysical Research Letters

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“…Below the boundary the electron population is dominated by atmospheric photoelectrons that are produced by solar ultraviolet and soft X-ray photons deep in the atmosphere and travel from the exobase (-180-km altitude) along magnetic field lines to the spacecraft, where they are measured. Although we do not measure thermal electrons (which have energies of-0.3 eV at the >170-km altitudes sampled by the ER), comparison of our measurements with observations by Pioneer Venus Orbiter [Spenner et al, 1980] suggests that this boundary is closely associated with the ionopause. Typically, an order-ofmagnitude density contrast is observed across the boundary at energies near 1 keV, which implies effective magnetic separation between the ionospheric and solar wind plasmas.…”

mentioning

confidence: 99%

Probing Mars' crustal magnetic field and ionosphere with the MGS Electron Reflectometer

Mitchell¹,

Lin²,

Mazelle³

et al. 2001

J. Geophys. Res.

336

434

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Abstract. The Electron Reflectometer (ER) on board Mars Global Surveyor measures the energy and angular distributions of solar wind electrons and ionospheric photoelectrons. These data can be used in conjunction with magnetometer data to probe Mars' crustal magnetic field and to study Mars' ionosphere and solar wind interaction. During aerobraking, ionospheric measurements were obtained in the northern hemisphere at high solar zenith angles (SZAs, typically -78ø). The ionopause was crossed at altitudes ranging from 180 km to over 800 km, with a median of 380 km. The 400-km-altitude polar mapping orbit allows observations at SZAs from 25 ø to 155 ø in both the northern and southern hemispheres. The near-planet ionosphere and magnetotail structure of the night hemisphere is dominated by the presence of intense crustal magnetic fields, which can exceed 200 nT at the spacecraft altitude. Closed field lines anchored to highly elongated crustal sources form "magnetic cylinders," which exclude solar wind plasma traveling up the magnetotail. When the spacecraft passes through one of these structures, the ER count rate falls to the instrumental background, representing an electron flux drop of at least two orders of magnitude. A map of these flux dropouts in longitude and latitude closely resembles a map of the crustal magnetic sources. When the crustal magnetic cylinders rotate into sunlight, they fill with ionospheric plasma. Since many of these crustal fields are locally strong enough to stand off the solar wind to altitudes well above 400 km, the ionosphere can extend much higher than would otherwise be possible in the absence of crustal fields. Even weak crustal fields may locally bias the median ionopause altitude, which provides an indirect method of detecting crustal fields using ER observations.

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“…[2] From the first measurements conducted in the Venus plasma environment with the Mariner 5 and the Venera spacecraft it was recognized that in addition to a bow shock upfront from the dayside ionosphere there is an another transition exterior to the ionosphere that extends along the flanks of the ionosheath downstream from the planet [Bridge et al, 1967;Vaisberg et al, 1976;Shefer et al, 1979;Romanov et al, 1979;Spenner et al, 1980;Pérez-de-Tejada et al, 1984]. Across this latter transition the plasma exhibits changes different from those at the bow shock in that the density of the solar wind and its magnetic field intensity become smaller in its downstream side exhibiting a rarefaction rather than a compression of the flow.…”

Section: Introductionmentioning

confidence: 99%

Plasma transition at the flanks of the Venus ionosheath: Evidence from the Venus Express data

et al. 2011

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[1] Measurements conducted with the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-4) instrument in the Venus Express spacecraft reveal the presence of a plasma transition within a boundary layer that extends along at the flanks of the Venus ionosheath and where the solar wind exhibits changes similar to those reported from previous missions (Mariner 5, Venera, and Pioneer Venus). At the plasma transition there is a sharp downstream decrease in the density of the solar wind electrons and a sudden increase in their temperature embedded within the boundary layer where more gradual changes in the speed, temperature, and density of the solar wind ions are observed. The ASPERA-4 data also show important fluxes of planetary ions measured downstream from the plasma transition and whose dominant velocity component is in the Sun-Venus direction. The speed of those ions is slower than the local solar wind speed and thus is different from that expected from the convective electric field acceleration in which both speed values should be comparable. The boundary layer is interpreted as representing a feature that results from the transport of solar wind momentum to the Venus upper ionosphere, and the ASPERA-4 data provide information on the kinetic properties of the eroded planetary ion population that is seen to stream mostly in the Sun-Venus direction. From the comparison of the ASPERA-4 measurements with those of the magnetic field obtained with the magnetometer of the Venus Express, it is found that in the near wake crossing of the plasma transition the magnetic field intensity decreases to lower values with downstream distance from the planet in agreement with measurements conducted with the Mariner 5 and the PVO. From the analysis of data for orbits with evidence of the plasma transition within the boundary layer, it is found that the momentum flux of planetary ions measured in the wake can be accounted for from the incident momentum flux of the solar wind protons implying an approximate balance as would result from the transport of solar wind momentum to the planetary particles.

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Observation of the Venus mantle, the boundary region between solar wind and ionosphere

Cited by 104 publications

References 24 publications

Evidence of electron impact ionization in the magnetic pileup boundary of Mars

Evidence of electron impact ionization in the magnetic pileup boundary of Mars

Probing Mars' crustal magnetic field and ionosphere with the MGS Electron Reflectometer

Plasma transition at the flanks of the Venus ionosheath: Evidence from the Venus Express data

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