Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p21a1324h&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P21A-1324
Other
5421 Interactions With Particles And Fields, 5435 Ionospheres (2459), 5440 Magnetic Fields And Magnetism, 6281 Titan, 6295 Venus
Scientific paper
Upward flow of ionospheric plasma into the induced magnetic tail of Venus was inferred some time ago from Pioneer Venus Orbiter (PVO) measurements, which were used to derive upward flow and acceleration of H+, D+ and O+ within the nightside ionosphere [1]. The measurements revealed that the polarization electric field in the nightside ionosphere produced the principal upward force on these light ions. Other electrodynamic forces were unimportant because the plasma beta in the nightside ionosphere is much greater than one. The resulting vertical flow of H+ and D+ was found to be the dominant escape mechanism of hydrogen and deuterium, corresponding to loss rates consistent with large oceans in early Venus [2]. Recently, plasma measurements made from Venus Express have clearly identified H+, D+ and O+ flowing away from Venus, down its magnetic tail [3]. The primary source of tail-flowing O+ is from the high altitude day-to-night flow system. Similarly, at unmagnetized Titan, ions have been observed to flow away from the moon along its induced magnetic tail by the Plasma Science Instrument (PLS) on Voyager 1 and the Casini Plasma Spectrometer (CAPS) on Cassini. In both cases, the ions have been inferred to be of ionospheric origin. Although the plasma beta is also greater than one in much of Titan's ionosphere, ion acceleration is expected to be more complex, especially because the subsolar point and the subflow points can be 180 degrees apart. Following what we learned at Venus, upward acceleration of light ions by the polarization electric field opposing gravity in the wake-side ionosphere of Titan is described. Additional electrodynamic forces resulting from the interaction of Saturn's magnetosphere with Titan's ionosphere will be examined using a recent hybrid model [4]. Comparisons between the wake-side flows on Venus and Titan will be made. [1] Hartle, R. E. and J. M. Grebowsky, Adv. Space Res., 15, (4)117, 1995. [2] Donahue, T. M. and R. E. Hartle, Geophys. Res. Lett., 19, 2449, 1992. [3] Barabash, S., et al., Nature, 450, 650, 2007. [4] Lipatov, A. S., E. C. Sittler, Jr. and R. E. Hartle, 2007 Fall AGU mtg., EOS, P23B-1366, 2007.
Hartle Richard E.
Lipatov Alexander S.
Sittler Edward C.
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