期刊
PLANETARY AND SPACE SCIENCE
卷 58, 期 3, 页码 327-350出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.pss.2009.09.017
关键词
Titan; Saturn's magnetosphere; Magnetodisc; Plasma; Magnetic fields; Ion composition
资金
- NASA [1243218]
- ADNET Systems Incorporate
- TRAX Corporation
- STFC [PP/E001173/1] Funding Source: UKRI
- Science and Technology Facilities Council [PP/E001173/1] Funding Source: researchfish
- UK Space Agency [PP/D00084X/1, ST/I002642/1] Funding Source: researchfish
We present new results of Cassini's T9 flyby with complementary observations from T18. Based on Cassini plasma spectrometer (CAPS) and Cassini magnetometer (MAG), compositional evidence shows the upstream flow for both T9 and T18 appears composed of light ions (H+ and H-2(+)), with external pressures similar to 30 times lower than that for the earlier TA flyby where heavy ions dominated the magnetospheric plasma. When describing the plasma heating and sputtering of Titan's atmosphere, T9 and T18 can be considered interactions of low magnetospheric energy input. On the other hand, T5. when heavy ion fluxes are observed to be higher than typical (i.e., TA), represents the limiting case of high magnetospheric energy input to Titan's upper atmosphere. Anisotropy estimates of the upstream flow are 1 < T-perpendicular to/T-parallel to < 3 and the flow is perpendicular to B, indicative of local picked up ions from Titan's H and H-2 coronae extending to Titan's Hill sphere radius. Beyond this distance the corona forms a neutral torus that surrounds Saturn. The T9 flyby unexpectedly resulted in observation of two wake crossings referred to as Events 1 and 2. Event 2 was evidently caused by draped magnetosphere field lines, which are scavenging pickup ions from Titan's induced magnetopause boundary with outward flux similar to 2 x 10(6) ions/cm(2)/s. The composition of this out flow is dominated by H-2(+) and H+ ions. Ionospheric flow away from Titan with ion flux similar to 7 x 10(6) ion/cm(2)/s is observed for Event 1. In between Events 1 and 2 are high energy field aligned flows of magnetosphere protons that may have been accelerated by the convective electric field across Titan's topside ionosphere. T18 observations are much closer to Titan than T9, allowing one to probe this type of interaction down to altitudes similar to 950 km. Comparisons with previously reported hybrid simulations are made. Published by Elsevier Ltd.
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