Extreme Forward Scattering Observed in Disk-averaged Near-infrared Phase Curves of Titan

Abstract Titan, with its thick and hazy atmosphere, is a key world in our solar system for understanding light scattering processes. NASA’s Cassini mission monitored Titan between 2004 and 2017, where the derived data set includes a large number of whole disk observations. Once spatially integrated, these whole disk observations reveal Titan’s phase-dependent brightness, which can serve as an analog for how hazy worlds might appear around other stars. To explore Titan’s phase curve, we present a pipeline for whole disk Titan observations acquired by the Cassini Visual and Infrared Mapping Spectrometer (VIMS) spanning 0.9–5.1 μ m. Application of the pipeline finds over 4400 quality spatially and spectrally resolved data cubes that were then integrated over Titan’s disk to yield phase curves spanning 2°–165° in phase angle. Spectra at near-full phase provide a useful approximation for Titan’s geometric albedo, thus extending the spectral coverage of previous work. Crescent phase brightness enhancements in the Cassini/VIMS phase curves are often more extreme than analogous results seen at optical wavelengths, which can be explained by atmospheric transparency and haze scattering processes. These results provide validation opportunities for exoplanet-focused spectral models and also shed light on how extreme aerosol forward scattering could influence exoplanet observations and interpretations.