Energy Deposition in Planetary Atmospheres by Charged Particles and Solar Photons

Abstract

We discuss here the energy deposition of solar FUV, EUV and X-ray photons, energetic auroral particles, and pickup ions. Photons and the photoelectrons that they produce may interact with thermospheric neutral species producing dissociation, ionization, excitation, and heating. The interaction of X-rays or keV electrons with atmospheric neutrals may produce core-ionized species, which may decay by the production of characteristic X-rays or Auger electrons. Energetic particles may precipitate into the atmosphere, and their collisions with atmospheric particles also produce ionization, excitation, and heating, and auroral emissions. Auroral energetic particles, like photoelectrons, interact with the atmospheric species through discrete collisions that produce ionization, excitation, and heating of the ambient electron population. Auroral particles are, however, not restricted to the sunlit regions. They originate outside the atmosphere and are more energetic than photoelectrons, especially at magnetized planets. The spectroscopic analysis of auroral emissions is discussed here, along with its relevance to precipitating particle diagnostics. Atmospheres can also be modified by the energy deposited by the incident pickup ions with energies of eV's to MeV's; these particles may be of solar wind origin, or from a magnetospheric plasma. When the modeling of the energy deposition of the plasma is calculated, the subsequent modeling of the atmospheric processes, such as chemistry, emission, and the fate of hot recoil particles produced is roughly independent of the exciting radiation. However, calculating the spatial distribution of the energy deposition versus depth into the atmosphere produced by an incident plasma is much more complex than is the calculation of the solar excitation profile. Here, the nature of the energy deposition processes by the incident plasma are described as is the fate of the hot recoil particles produced by exothermic chemistry and by knock-on collisions by the incident ions.

Comprehensive calculation of the energy per ion pair or <I>W</I> values for five major planetary upper atmospheres

“…The results shown in Table 1 and Fig. 3 for N 2 , O 2 and O are in good agreement with previous theoretical studies (Green et al, 1977;Sergienko and Ivanov, 1993) except with that of Fox et al (2008). Within the error bars, the results for H, H 2 and He are identical to those of Dalgarno et al (1999) and Fox et al (2008).…”

Model insights into energetic photoelectrons measured at Mars by MAVEN

“…Coulomb collisions generate heating of the thermal electrons and lead to enhanced electron temperatures [cf. Schunk and Nagy, 2009;Fox et al, 2008;Chen et al, 1978]. Figure 3b shows model-SWEA comparisons on 3 March 2015 for which the solar zenith angle was 72°.…”

“…Fox et al, 2008]. Photoelectrons (or suprathermal electrons) result from the photoionization of neutral species (CO 2 , CO, N 2 , and O):…”

Kinetic-energy release of fragments from electron-impact dissociation of the molecular hydrogen ion and its isotopologues

“…These collision processes are among the most important for determining fusion and lowtemperature plasma dynamics and properties, and can also be used to control plasma conditions [1,2]. Information about the KER distribution is used to determine energy deposition and reactivity in the respective media, which is important in the fields of radiotherapy [3][4][5][6] and astrophysics [7].…”