| Summary: | At the beginning of the Cassini mission, the ISS (Imaging Science Subsystem) and CIRS (Composite Infra-Red Spectrometer) instruments discovered a geologically active region at the south pole of Saturn's moon Enceladus (e.g. Porco et al., 2005). Plumes venting material emanate from this region. Six years later, on November 6, 2011, the first-ever Synthetic Aperture Radar (SAR) image of Enceladus was acquired during the E16 flyby of the moon at the wavelength of 2-cm (Mitchell et al., AGU 2011). The SAR swath is located within the seemingly young South Pole Terrains, not far from the active sulci also known as the "tiger stripes" identified as the sources of the plumes. Concurrently to the SAR image, radiometry data were collected in the passive mode of the instrument with a ground footprint of 25-40 km across the track and ~5 km along. The Cassini radiometer records the thermal emission from the surface in the microwave domain, at 2-cm. More specifically, it measures the brightness temperature of the surface that varies both with the emissivity and the vertical temperature profile below the surface down to a depth, which depends on the electrical properties of the subsurface. Typically, radio instruments sense 10 to 100 wavelengths into an icy crust and can thus provide unique insight into the compositional, thermal and physical (porosity, roughness) state of planetary regoliths at depths much greater than the ones sampled by thermal IR spectrometers. In particular, microwave radiometer can be used to detect possible endogenic activity beneath the surface. The measured calibrated brightness temperatures during E16 cover a range from 33 to 60 K. In order to analyze these dataset, we have modeled the expected thermal emission from Enceladus' surface. In absence of endogenic emission, the temperature structure of any airless satellite results from a balance between solar insolation, heat transport within the subsurface and reradiation outward. The developed thermal model accounts not only for the diurnal but also ...
|
|---|