Re-analysis of the Cassini RPWS/LP data in Titan’s ionosphere. Part I:
detection of several electron populations
Abstract
Current models of Titan’s ionosphere have difficulties in explaining the
observed electron density and/or temperature. In order to get new
insights, we re-analyzed the data taken in the ionosphere of Titan by
the Cassini Langmuir probe (LP), part of the Radio and Plasma Wave
Science (RPWS) instrument. This is the first of two papers that present
the new analysis method (current paper) and statistics on the whole
dataset. We suggest that between 2 and 4 electron populations are
necessary to fit the data. Each population is defined by a potential, an
electron density and an electron temperature and is easily visualized by
a dinstinct peak in the second derivative of the electron current, which
is physically related to the electron energy distribution function
(Druyvesteyn method). The detected populations vary with solar
illumination and altitude. We suggest that the 4 electron populations
are due to photo-ionization, magnetospheric particles, dusty plasma and
electron emission from the probe boom, respectively.