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Title:
Enceladus: The likely dominant nitrogen source in Saturn's magnetosphere
Authors:
Smith, H. T.; Johnson, R. E.; Sittler, E. C.; Shappirio, M.; Reisenfeld, D.; Tucker, O. J.; Burger, M.; Crary, F. J.; McComas, D. J.; Young, D. T.
Affiliation:
AA(Division of Space Science and Engineering, Southwest Research Institute, 9503 W Commerce, San Antonio, TX 78227-1301, USA), AB(Engineering Physics, University of Virginia, Thornton Hall, Charlottesville, VA 22904, USA), AC(NASA/Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA), AD(NASA/Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA), AE(Department of Physics and Astronomy, University of Montana, 32 Campus Drive, Missoula, MT 59812, USA), AF(Engineering Physics, University of Virginia, Thornton Hall, Charlottesville, VA 22904, USA), AG(NASA/Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA), AH(Division of Space Science and Engineering, Southwest Research Institute, 9503 W Commerce, San Antonio, TX 78227-1301, USA), AI(Division of Space Science and Engineering, Southwest Research Institute, 9503 W Commerce, San Antonio, TX 78227-1301, USA), AJ(Division of Space Science and Engineering, Southwest Research Institute, 9503 W Commerce, San Antonio, TX 78227-1301, USA)
Publication:
Icarus, Volume 188, Issue 2, p. 356-366. (Icarus Homepage)
Publication Date:
06/2007
Origin:
ELSEVIER
DOI:
10.1016/j.icarus.2006.12.007
Bibliographic Code:
2007Icar..188..356S

Abstract

The spatial distribution of N+ in Saturn's magnetosphere obtained from Cassini Plasma Spectrometer (CAPS) data can be used to determine the spatial distribution and relative importance of the nitrogen sources for Saturn's magnetosphere. We first summarize CAPS data from 15 orbits showing the spatial and energy distribution of the nitrogen component of the plasma. This analysis re-enforces our earlier discovery [Smith, H.T., Shappirio, M., Sittler, E.C., Reisenfeld, D., Johnson, R.E., Baragiola, R.A., Crary, F.J., McComas, D.J., Young, D.T., 2005. Geophys. Res. Lett. 32 (14). L14S03] that Enceladus is likely the dominant nitrogen source for Saturn's inner magnetosphere. We also find a sharp enhancement in the nitrogen ion to water ion ratio near the orbit of Enceladus which, we show, is consistent with the presence of a narrow Enceladus torus as described in [Johnson, R.E., Liu, M., Sittler Jr., E.C., 2005. Geophys. Res. Lett. 32. L24201]. The CAPS data and the model described below indicate that N+ ions are a significant fraction of the plasma in this narrow torus. We then simulated the combined Enceladus and Titan nitrogen sources using the CAPS data as a constraint. This simulation is an extension of the model we employed earlier to describe the neutral tori produced by the loss of nitrogen from Titan [Smith, H.T., Johnson, R.E., Shematovich, V.I., 2004. Geophys. Res. Lett. 31 (16). L16804]. We show that Enceladus is the principal nitrogen source in the inner magnetosphere but Titan might account for a fraction of the observed nitrogen ions at the largest distances discussed. We also show that the CAPS data is consistent with Enceladus being a molecular nitrogen source with a nitrogen to water ratio roughly consistent with INMS [Waite, J.H., and 13 colleagues, 2006. Science 311 (5766), 1419 1422], but out-gassing of other nitrogen-containing species, such as ammonia, cannot be ruled out.
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