Investigating the Interiors of Small Bodies and Ocean Worlds with Spacecraft Swarms and Schumann Resonances (original) (raw)
A Schumann Resonance is an electromagnetic oscillation excited in a closed waveguide formed by multiple reflecting layers at or near the surface of a planetary body. The waveguide, for spherical bodies with uniform reflecting layers, is a resonant cavity with a fundamental wavelength ∼ the circumference of the body. A Schumann Resonance was detected on Titan at ∼36 Hz by the Huygens probe, with the resonant cavity being formed by Titan’s and subsurface ocean and the excitation thought to result from currents in the ionosphere induced by the advected Saturnian magnetic field. The same mechanisms should apply to Europa, leading to a prediction of a Schumann resonance between near-surface charged particles and the subsurface ocean which can be used to explore the subsurface of that ocean world. Similar considerations lead to the possibility of full-body Schumann-type resonances on small bodies (asteroids and comets), with the reflecting layer being provided by photo-disassociated electrons at the surface.
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Planetary and Space Science, 2007
The propagation of extremely low frequency (ELF) electromagnetic waves in the Earth's ionospheric cavity and the associated resonance phenomena have been extensively studied, in relation with lightning activity. We perform a similar investigation for Titan, the largest moon of Saturn. There are important differences between Earth and Titan, as far as the cavity geometry, the atmospheric electron density profile, and the surface conductivity are concerned. We present an improved 3D finite element model that provides an estimate of the lowest eigenfrequencies, associated quality factors (Q-factors), and ELF electric field spectra. The data collected by the electric antenna of the Permittivity, Waves, and Altimetry (PWA) instrument reveals the existence of a narrow-band signal at about 36 Hz during the entire descent of Huygens upon Titan. We assess the significance of these measurements against the model predictions, with due consideration to the experimental uncertainties.
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