Details

Autor(en) / Beteiligte

• Janssen, M.A.
• Le Gall, A.
• Lopes, R.M.
• Lorenz, R.D.
• Malaska, M.J.
• Hayes, A.G.
• Neish, C.D.
• Solomonidou, A.
• Mitchell, K.L.
• Radebaugh, J.
• Keihm, S.J.
• Choukroun, M.
• Leyrat, C.
• Encrenaz, P.J.
• Mastrogiuseppe, M.

Titel

Titan’s surface at 2.18-cm wavelength imaged by the Cassini RADAR radiometer: Results and interpretations through the first ten years of observation

Ist Teil von

• Icarus (New York, N.Y. 1962), 2016-05, Vol.270, p.443-459

Ort / Verlag

Elsevier Inc

Erscheinungsjahr

2016

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• •Titan’s thermal emission at 2-cm λ has been globally measured and calibrated.•A microwave penetration depth ∼1m has been determined from the seasonal variation.•The radar-dark surface is likely of organic composition this deep or more.•Titan’s radar-bright regions are likely due to surface or near-surface water ice.•The main source of microwave reflectivity is sub-surface volume scattering. A comprehensive calibration and mapping of the thermal microwave emission from Titan’s surface is reported based on radiometric data obtained at 2.18-cm wavelength by the passive radiometer included in the Cassini RADAR instrument. Compared to previous work, the present results incorporate the much larger data set obtained in the approximately ten years following Saturn Orbit Insertion. Brightness temperature data including polarization were accumulated by segments in Titan passes from Ta (October 2004) through T98 (February 2014). The observational segments were analyzed to produce a mosaic of effective dielectric constant based on the measurement of thermal polarization covering 76% of the surface, and brightness temperature at normal incidence covering Titan’s entire surface. As part of the mosaicking process we also solved for the seasonal variation of physical temperature with latitude, which we found to be smaller by a factor of 0.87±0.05 in relative amplitude compared to that reported in the thermal infrared by Cassini’s Composite Infrared Spectrometer (CIRS). We used the equatorial temperature obtained by the Huygens probe and the seasonal dependence with latitude from CIRS to convert the brightness mosaic to absolute emissivity, from which we could infer global thermophysical properties of the surface in combination with the dielectric mosaic. We see strong evidence for subsurface (volume) scattering as a dominant cause of the radar reflectivity in bright regions, and elsewhere a surface composition consistent with the slow deposition and processing of organic compounds from the atmosphere. The presence of water ice in the near subsurface is strongly indicated by the high degree of volume scattering observed in radar-bright regions (e.g., Hummocky/mountainous terrains) constituting ∼10% of Titan’s surface. A thermal analysis allowed us to infer a mean 2.18-cm emission depth in the range 40–100cm for the dominant radar-dark terrains (the remainder of Titan’s surface) at all latitudes of Titan, consistent with the deposition and possible processing and redistribution of tholin-like atmospheric photochemical products.