The thermosphere and ionosphere of Venus

Our knowledge of the upper atmosphere and ionosphere of Venus and its interaction with the solar wind has advanced dramatically over the last decade, largely due to the data obtained during the Pioneer Venus mission and to the theoretical work that was motivated by this data. Most of this information was obtained during the period 1978 through 1981, when the periapsis of the Pioneer Venus Orbiter (PVO) was still in the measurable atmosphere. However, solar gravitational perturbations will again lower the PVO periapsis into the upper atmosphere in September 1992, prior to the destruction of the spacecraft toward the end of this year. The physics and chemistry of the thermosphere and ionosphere of Venus are reviewed

Ion distribution functions in the vicinity of comet Giacobini‐Zinner

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95028/1/grl3117.pd

Ion energetics in the inner coma of comet Halley

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94666/1/grl3718.pd

The precipitation of energetic heavy ions into the upper atmosphere of Jupiter

Evidence for auroral particle precipitation at Jupiter was provided by the ultraviolet spectrometers onboard the Voyagers 1 and 2 spacecraft and by the International Ultraviolet Explorer (IUE). Magnetospheric measurements made by instruments onboard the Voyager spacecraft show that energetic sulfur and oxygen ions are precipitating into the upper atmosphere of Jupiter. A theoretical model has been constructed describing the interaction of precipitating oxygen with the Jovian atmosphere. The auroral energy is deposited in the atmosphere by means of ionization, excitation, and dissociation and heating of the atmospheric gas. Energetic ion and electron precipitation are shown to have similar effects on the atmosphere and ionosphere of Jupiter

The role of proton precipitation in Jovian aurora: Theory and observation

It was proposed that the Jovian auroral emissions observed by Voyager spacecraft could be explained by energetic protons precipitating into the upper atmosphere of Jupiter. Such precipitation of energetic protons results in Doppler-shifted Lyman alpha emission that can be quantitatively analyzed to determine the energy flux and energy distribution of the incoming particle beam. Modeling of the expected emission from a reasonably chosen Voyager energetic proton spectrum can be used in conjunction with International Ultraviolet Explorer (IUE) observations, which show a relative lack of red-shifted Lyman alpha emission, to set upper limits on the amount of proton precipitation taking place in the Jovian aurora. Such calculations indicate that less than 10 percent of the ultraviolet auroral emissions at Jupiter can be explained by proton precipitation

A time‐dependent theoretical model of the polar wind: Preliminary results

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95137/1/grl2867.pd

Angular distribution of electrons elastically scattered from CH4

Differential elastic (vibrationally) scattering cross sections of CH4 by electron impact have been measured using a modulated crossed-beam method. The energy and angular range covered were from 5 to 50 eV and from 12 to 156', respectively. The integrated and momentum transfer cross sections were obtained from the differential cross sections. The present results are compared with the earlier data of Tanaka et al. (1982) and with theoretical results of Lima et al. (1985) and Jain and Thompson (1982). Some discrepancies were found in the measurements and theoretical results.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48850/2/jbv23i2p293.pd

Pressure Gradients Driving Ion Transport in the Topside Martian Atmosphere

An edited version of this paper was published by AGU. Copyright 2019 American Geophysical Union.Magnetic and thermal pressure gradient forces drive plasma flow in the topside ionosphere of Mars. Some of this flow can contribute to ion loss from the planet and thus affect atmospheric evolution. MAVEN measurements of the magnetic field, electron density, and electron temperature, taken over a 3‐year time period, are used to obtain averaged magnetic and thermal pressures in the topside ionosphere versus altitude, solar zenith angle, and latitude. Magnetic pressures are several times greater than thermal pressures for altitudes greater than about 300 km; that is, the plasma beta is less than one. The total pressure increases with altitude in the ionosphere and decreases with increasing solar zenith angle. Using these pressure patterns in the dayside ionosphere to estimate the pressure gradient force in the fluid momentum equation, we estimate horizontal day‐to‐night plasma flow speeds of a few kilometers per second near 400 km

Unusual electron density profiles observed by Cassini radio occultations in Titan's ionosphere: Effects of enhanced magnetospheric electron precipitation?

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95188/1/jgra21399.pd

Estimates of Ionospheric Transport and Ion Loss at Mars

Ion loss from the topside ionosphere of Mars associated with the solar wind interaction makes an important contribution to the loss of volatiles from this planet. Data from NASA’s Mars Atmosphere and Volatile Evolution mission combined with theoretical modeling are now helping us to understand the processes involved in the ion loss process. Given the complexity of the solar wind interaction, motivation exists for considering a simple approach to this problem and for understanding how the loss rates might scale with solar wind conditions and solar extreme ultraviolet irradiance. This paper reviews the processes involved in the ionospheric dynamics. Simple analytical and semiempirical expressions for ion flow speeds and ion loss are derived. In agreement with more sophisticated models and with purely empirical studies, it is found that the oxygen loss rate from ion transport is about 5% (i.e., global O ion loss rate of Qion ≈ 4 × 1024 s−1) of the total oxygen loss rate. The ion loss is found to approximately scale as the square root of the solar ionizing photon flux and also as the square root of the solar wind dynamic pressure. Typical ion flow speeds are found to be about 1 km/s in the topside ionosphere near an altitude of 300 km on the dayside. Not surprisingly, the plasma flow speed is found to increase with altitude due to the decreasing ion‐neutral collision frequency.Key PointsOxygen ion loss from the ionosphere of Mars is mainly driven by magnetic forces generated by the solar wind interactionGlobal ion loss from Mars scales approximately as the square root of both the upstream solar wind pressure and solar ionizing photon fluxIon flow speeds in the ionosphere increase with altitude and with solar wind pressurePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140009/1/jgra53859.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/140009/2/jgra53859_am.pd