First results from the Cassini radio occultations of the Titan ionosphere

摘要

The first four sets of radio occultations of the Titan's ionosphere were obtained by the Cassini spacecraft between March 2006 and May 2007. These occultations occurred at middle and high latitudes, at solar zenith angles from about 86° to 96°. The main ionospheric peak was seen, as expected from modeling and previous observations, near 1200 km, with a density of about 1–3 × 103 cm_3. A consistent ledge near 1000 km was also seen, and one of the polar observations found a significant (～3 × 103 cm_3) layer in the region of 500–600 km. This layer also is seen in other observations with a density varying from about 0.7 to 1.7 × 103 cm_3, suggesting a variable production source (or sources) for this peak.