University of Kansas Titan Studies

Image courtesy of NASA/JPL-Caltech.

DRAFT

Titan's Ionosphere: Model Comparisons with Cassini Ta Data

T. E. Cravens, I. P. Robertson, J. Clark, J.-E. Wahlund, J. H.Waite Jr., S. A. Ledvina, H. B. Niemann, R. V. Yelle, W. T. Kasprzak, J. G. Luhmann, R. L. McNutt, W.-H. Ip, V. de la Haye, I. Muller-Wordag, D. T. Young, and A. J. Coates

(The final version of this paper appears in Geophysical Research Letters, 32, no. 12, L12108, doi: 10.1029/2005GL023249. Copyright 2005 American Geophysical Union.)

Abstract with link to full article on the AGU website.

Abstract. On October 26, 2004, during its first encounter with Titan (Ta), the Cassini Orbiter moved from the dayside to the nightside with a closest approach altitude of 1174 km. In situ measurements of the main part of Titan's ionosphere were made by the Langmuir probe on the Cassini Radio and Plasma Wave Experiment (RPWS), while the Ion and Neutral Mass Spectrometer (INMS) measured the main constituents of the neutral atmosphere. The results of model calculations of Titan's ionosphere for Ta encounter conditions (e.g., near the terminator) are presented in this paper. The paper includes comparisons of calculated and measured electron densities along the spacecraft track. Ionization both by solar radiation and by incoming energetic electrons from Saturn's magnetosphere are needed to obtain good agreement between the measured and calculated electron densities.

• Introduction
• Model Description
• Results
• Discussion and Conclusions
• References

Figures:

	Figure 1. Production rate profiles for N2+ ions for incident magnetospheric electron fluxes and for a parabolic magnetic field line configuration. The magnetospheric electron populations considered have electron densities and temperatures of: (ne, Te) = (0.1 cm-3; 200 eV), (0.1 cm-3; 100 eV), (0.2 cm-3; 50 eV), (0.3 cm-3; 25 eV).
	Figure 2. Time histories of the electron density along the Cassini Orbiter trajectory are shown for the 4 magnetospheric cases listed in Figure 1. Solar zenith angle and altitude along the track are also shown, but no ionization from solar radiation was included. Electron densities measured by the RPWS experiment [Wahlund et al., 2005] are also shown.
	Figure 3. Calculated radial/vertical electron density profiles for solar ionization only (no magnetospheric electron contribution) and at several times (in units of seconds) and solar zenith angles for the Cassini Orbiter. The solar zenith angle varies from 58.9 deg. (for t = -400 s) to 108.6 deg. (t = +200 s). The solar zenith angle for closest approach (time t = 0 s) was 91.1 deg. The line and open circles indicate the relevant densities for the spacecraft track.
	Figure 4. The same as Figure 2 but the model electron densities are for calculations for two cases: (1) ionization only by solar radiation (Solar Flux 1) and (2) ionization from both solar radiation (Solar Flux 1) and from incident magnetospheric electrons with a temperature of 100 eV.

ACKNOWLEDGMENTS. Support from the NASA Cassini project is acknowledged. Model development at the University of Kansas was supported by NASA Planetary Atmospheres Grant NNG04GQ58G and NSF grant ATM-0234271.

Return to Titan Studies main page.
Return to Space Physics home page.

Last modified Sept. 8, 2006 Tizby Hunt-Ward tizby@ku.edu