Interpreting Ganymede’s Microwave Emission: Modeling Emission and Scattering From Bright Terrain

An advanced microwave radiative transfer model is developed for Ganymede by enhancing the Microwave Emission Model of Layered Snowpacks (MEMLS). It integrates topographic effects into the heat conduction equation for temperature profiles and treats ice as Rayleigh scatterers to address volume scattering. Channels 4–6 of Juno Microwave Radiometer data, sensitive to the surface diurnal layer, are applied to investigate the microwave emission of bright terrains of Ganymede. Comparisons between observed and simulated brightness temperatures (TBs) reveal no significant Rayleigh volume scattering across 5-22 GHz in either Xibalba Sulcus (XS) or Tros crater. To reconcile the discrepancy between observed and modeledTBs, a surface dust layer is introduced into the model. This addition successfully explains the suppressedTBsobserved in bright terrains, suggesting the presence of materials with a higher dielectric constant (such as silicates or salts) than pure water ice. For the XS region, the real part of the dielectric constant of the dust layer must be at least 5 to achieve approximate agreement between the modeled and observedTB. While For Tros crater, with lower TB, requires an exceptionally high value (real part > 15). The impact of antenna patterns at 5 GHz and 22 GHz on observedTBsis quantified. An anomalous 5 GHz TB depression relative to 22 GHz TB in XS is attributed to antenna pattern variations between frequencies. Topographic effects are negligible at Tros crater due to its large diameter-to-depth ratio, unlike smaller craters like Achelous, where topography significantly influences thermal behavior.