Extreme Forward Scattering Observed in Disk-Averaged Near-Infrared Phase Curves of Titan

TL;DR

This study analyzes Titan's near-infrared phase curves from Cassini data, revealing extreme forward scattering effects caused by atmospheric haze, which has implications for exoplanet observation and modeling.

Contribution

It introduces a pipeline for processing Cassini VIMS data to produce detailed Titan phase curves across a broad spectral range, highlighting extreme aerosol scattering effects.

Findings

Crescent phase brightness enhancements are more extreme in near-infrared than optical wavelengths.

Atmospheric haze causes significant forward scattering, affecting observed brightness.

Results validate and inform exoplanet spectral models involving hazy atmospheres.

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 dataset 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 $\mu$m. Application of the pipeline finds over 4,400 quality spatially- and spectrally-resolved datacubes that were then integrated over Titan's disk to yield phase curves spanning 2\degree--165\degree 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.