Temperature variations in Titan's upper atmosphere: Impact on Cassini/Huygens
1Space Research Institute, Austrian Academy of Sciences, A-8042 Graz, Austria
2LESIA-Observatoire de Paris-Meudon, 92195, Meudon Cedex, France
3ESA Research and Scientific Support Department, ESTEC, 2200 AG Noordwijk, The Netherlands
4Planetary and Space Sciences Research Institute, The Open University, Milton Keynes, MK7 6AA, UK
Abstract. Temperature variations of Titan's upper atmosphere due to the plasma interaction of the satellite with Saturn's magnetosphere and Titan's high altitude monomer haze particles can imply an offset of up to ±30K from currently estimated model profiles. We incorporated these temperature uncertainties as an offset into the recently published Vervack et al. (2004) (Icarus, Vol. 170, 91-112) engineering model and derive extreme case (i.e. minimum and maximum profiles) temperature, pressure, and density profiles. We simulated the Huygens probe hypersonic entry trajectory and obtain, as expected, deviations of the probe trajectory for the extreme atmosphere models compared to the simulation based on the nominal one. These deviations are very similar to the ones obtained with the standard Yelle et al. (1997) (ESA SP-1177) profiles. We could confirm that the difference in aerodynamic drag is of an order of magnitude that can be measured by the probe science accelerometer. They represent an important means for the reconstruction of Titan's upper atmospheric properties. Furthermore, we simulated a Cassini low Titan flyby trajectory. No major trajectory deviations were found. The atmospheric torques due to aerodynamic drag, however, are twice as high for our high temperature profile as the ones obtained with the Yelle maximum profile and more than 5 times higher than the worst case estimations from the Cassini project. We propose to use the Cassini atmospheric torque measurements during its low flybys to derive the atmospheric drag and to reconstruct Titan's upper atmosphere density, pressure, and temperature. The results could then be compared to the reconstructed profiles obtained from Huygens probe measurements. This would help to validate the probe measurements and decrease the error bars.
Kazeminejad, B., Lammer, H., Coustenis, A., Witasse, O., Fischer, G., Schwingenschuh, K., Ball, A. J., and Rucker, H. O.: Temperature variations in Titan's upper atmosphere: Impact on Cassini/Huygens, Ann. Geophys., 23, 1183-1189, doi:10.5194/angeo-23-1183-2005, 2005.