IAFE   05512
INSTITUTO DE ASTRONOMIA Y FISICA DEL ESPACIO
Unidad Ejecutora - UE
artículos
Título:
Saturn's magnetospheric interaction with Titan as defined by Cassini encounters T9 and T18: New results
Autor/es:
SITTLER, E. C.; HARTLE, R. E.; JOHNSON, R. E.; COOPER, J. F.; LIPATOV, A. S.; BERTUCCI, C.; COATES, A. J.; SZEGO, K.; SHAPPIRIO, M.; SIMPSON, D. G.; WAHLUND, J.-E.
Revista:
PLANETARY AND SPACE SCIENCE
Editorial:
PERGAMON-ELSEVIER SCIENCE LTD
Referencias:
Año: 2010 p. 327 - 350
ISSN:
0032-0633
Resumen:
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 H2+), with external pressures 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⊥/T‖<3 and the flow is
perpendicular to B, indicative of local picked up ions from Titan's H
and H2 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 2×106 ions/cm2/s. The
composition of this out flow is dominated by H2+
and H+ ions. Ionospheric flow away from Titan with ion flux
7×106 ion/cm2/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 950 km. Comparisons with previously
reported hybrid simulations are made.