Geological Evolution of Titan's Equatorial Regions: Possible Nature and Origin of the Dune Material

Thèmes de recherche:
Année:
2018
Auteurs:
Journal:
JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS
Volume:
123
Numéro:
5
Pages:
1089-1112
Mois:
Mai
ISSN:
2169-9097
Résumé:
In 13years, infrared observations from the Visual and Infrared Mapping
Spectrometer onboard Cassini provided significant hints about the
spectral and geological diversity of Titan's surface. The analysis of
the infrared (IR) signature of spectral units enables constraining the
surface composition, which is crucial for understanding possible
interactions between Titan's interior, surface, and atmosphere. Here we
investigate a selection of areas in the equatorial regions, imaged by
Cassini's instruments, which exhibit an apparent transition from the
Visual and Infrared Mapping Spectrometer IR-bright to the IR-blue and
IR-brown units (from false-color composites using red: 1.57/1.27m,
green: 2.01/1.27m, and blue: 1.27/1.08m). By applying an updated
radiative transfer model, we extract the surface albedo of IR units
identified in these regions. Then, we compare them with synthetic
mixtures of two expected components on Titan's surface, namely, water
ice and laboratory tholins. This allows us to reconnect the derived
composition and grain size information to the geomorphology observed
from Radio Detection and Ranging instrument (RADAR)/Synthetic Aperture
Radar images. We interpret IR-bright units as hills and plains coated by
organic material and incised by fluvial networks. Erosion products are
transported downstream to areas where IR-blue units are seen near the
IR-bright units. These units, enriched in water ice, are most likely
outwash plains hosting debris from fluvial erosion. Farther away from
the IR-bright units, the IR-brown units are dominantly made of organics
with varied grain sizes, ranging from dust- to sand-sized particles that
form the dune fields. The transition areas therefore exhibit trends in
water ice content and grain size supported by geomorphological
observations.