INVESTIGADORES
BERTUCCI Cesar
artículos
Título:
New insights on Titan's plasma-driven Schumann resonance inferred from Huygens and Cassini data
Autor/es:
BÉGHIN, C.; CANU, P.; KARKOSCHKA, E.; SOTIN, C.; BERTUCCI, C.; KURTH, W. S.; BERTHELIER, J. J.; GRARD, R.; HAMELIN, M.; SCHWINGENSCHUH, K.; SIMÕES, F.
Revista:
PLANETARY AND SPACE SCIENCE
Editorial:
PERGAMON-ELSEVIER SCIENCE LTD
Referencias:
Año: 2009 p. 1872 - 1888
ISSN:
0032-0633
Resumen:
After a preliminary analysis of the low-frequency data collected with
the electric antenna of the Permittivity, Wave and Altimetry (PWA)
experiment onboard the Huygens Probe that landed on Titan on 14 January,
2005, it was anticipated in a previous article [Béghin et al.,
2007. A Schumann-like resonance on Titan driven by Saturn's
magnetosphere possibly revealed by the Huygens Probe. Icarus, 191,
251-266] that the Extremely Low-Frequency (ELF) signal at around 36 Hz
observed throughout the descent, might have been generated in the upper
ionosphere of Titan, driven by a plasma instability mechanism associated
with the co-rotating Kronian plasma flow. The involved process was
proposed as the most likely source of a Schumann resonance in the moon's
atmospheric cavity, the second eigenmode of which is actually found by
models to occur at around 36 Hz. In this paper, we present a thorough
analysis of this signal based upon the Huygens Probe attitude data
deduced from the Descent Imager Spectral Radiometer (DISR), and relevant
measurements obtained from the Radio Plasma Wave Science (RPWS)
experiment and from the magnetometer (MAG) onboard Cassini orbiter
during flybys of Titan. We have derived several coherent characteristics
of the signal which confirm the validity of the mechanism initially
proposed and provide new and significant insights about such a unique
type of Schumann resonance in the solar system. Indeed, the 36 Hz signal
contains all the characteristics of a polarized wave, with the measured
electric field horizontal component modulated by the antenna rotation,
and an altitude profile in agreement with a Longitudinal Section
Electric (LSE) eigenmode of the atmospheric cavity. In contrast to
Earth's conditions where the conventional Transverse Magnetic mode is
considered, the LSE mode appears to be the only one complying with the
observations and the unexpected peculiar conditions on Titan. These
conditions are essentially the lack of any lightning activity that can
be ascertained from Cassini observations, the presence of an ionized
layer centered around 62 km altitude that was discovered by the PWA
instrumentation, and the existence of a subsurface conducting boundary
which is mandatory for trapping ELF waves. A simple theoretical model
derived from our analysis places tentatively consequential constraints
on the conductivity profile in the lower ionosphere. It is also
consistent with the presence of a conductive water ocean below an icy
crust some tens of kilometers thick.