Field-aligned photoelectron energy peaks at high altitude and on the nightside of Titan
JGR-IMPACT FACTOR. 3,71 https://agupubs.onlinelibrary.wiley.com/journal/21699100
ISSN 2169-9100

The ionization of N2 by strong solar He II 30.4 nm photons produces distinctive spectral
22 peaks near 24.1 eV in Titan s upper atmosphere, which have been observed by the Elec23
tron Spectrometer (ELS) as part of the Cassini Plasma Spectrometer (CAPS). The ELS
observations reveal that, in addition to the dayside, photoelectron peaks were also detected
on the deep nightside where photoionization is switched off, as well as at sufficiently high
altitudes where the ambient neutral density is low.

The ionization of N2 by strong solar He II 30.4 nm photons produces distinctive spectral
peaks near 24.1 eV in Titan s upper atmosphere, which have been observed by the Electron Spectrometer (ELS) as part of the Cassini Plasma Spectrometer (CAPS). The ELS observations reveal that, in addition to the dayside, photoelectron peaks were also detected on the deep nightside where photoionization is switched off, as well as at sufficiently high altitudes where the ambient neutral density is low. These photoelectron peaks are unlikely to be produced locally but instead must be contributed by transport along the magnetic field lines from their dayside source regions. In this study, we present a statistical survey of all photoelectron peaks identified with an automatic finite impulse response algorithm based on the available ELS data accumulated during 56 Titan flybys.