Density spikes in Titan’s upper ionosphere

Titan, the largest moon of Saturn, has a dense and nitrogen-rich atmosphere, which is similar to that of early Earth before lived evolved. Solar EUV radiation and energetic particles ionizes the atmosphere and thereby forming a layer of plasma, the ionosphere, in the uppermost part of the atmosphere. The Cassini spacecraft flew past the moon Titan 127 times during its 14-year mission in the Saturn system. During most of these close flybys Cassini entered the ionosphere and some reached the ionospheric peak, located at some 1400 km above the moon surface. With the Langmuir probe instrument, we could study the plasma properties, e.g. ion and electron density, temperature etc., and a very dynamic ionospheric structure was found. In particular, significant and apparently sporadic density spikes in the upper ionosphere were found. These density peaks are manifested as a sudden increase in the measured density by some 10-100 cm^-3 over a time period of roughly minutes. These have so far been left unattended in our studies of Titan. We will present some statistics on their appearance and initial result on the mechanism forming them.