Detection of negative ions in the deep ionosphere of Titan during the Cassini T70 flyby

Abstract

We present radio and plasma wave science (RPWS) Langmuir probe (LP) observations that give evidence for a population of heavy, negative ions at altitudes below 900km in Titan's ionosphere during the Cassini T70 flyby. The negative ion density in this region is comparable to, or higher than, the electron density of 760cm-3. Both positive and negative ions are moving with a velocity of at least a few hundred ms-1 relative to Titan. We show two limiting cases where we have analysed RPWS/LP ion measurements. The data can be interpreted as either that a population of negative ions with density comparable to the electron density is present, moving at a very high (>2kms-1) velocity, or that the ion population is moving at a few hundred ms-1, but with a density an order of magnitude larger than the electron density in the same region. © Copyright 2012 by the American Geophysical Union.