We investigate Titan's low‐latitude and midlatitude surface using spectro‐imaging near‐infrared data from Cassini/Visual and Infrared Mapping Spectrometer. We use a radiative transfer code to first evaluate atmospheric contributions and then extract the haze and the surface albedo values of major geomorphological units identified in Cassini Synthetic Aperture Radar data, which exhibit quite similar spectral response to the Visual and Infrared Mapping Spectrometer data. We have identified three main categories of albedo values and spectral shapes, indicating significant differences in the composition among the various areas. We compare with linear mixtures of three components (water ice, tholin‐like, and a dark material) at different grain sizes. Due to the limited spectral information available, we use a simplified model, with which we find that each albedo category of regions of interest can be approximately fitted with simulations composed essentially by one of the three surface candidates. Our fits of the data are overall successful, except in some cases at 0.94, 2.03, and 2.79 μm, indicative of the limitations of our simplistic compositional model and the need for additional components to reproduce Titan's complex surface. Our results show a latitudinal dependence of Titan's surface composition, with water ice being the major constituent at latitudes beyond 30°N and 30°S, while Titan's equatorial region appears to be dominated partly by a tholin‐like or by a very dark unknown material. The albedo differences and similarities among the various geomorphological units give insights on the geological processes affecting Titan's surface and, by implication, its interior. We discuss our results in terms of origin and evolution theories.

In 13 years, 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: 1.57/1.27 μm, green: 2.01/1.27 μm, and blue: 1.27/1.08 μm). 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.

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Previous studies of NASA's Magellan radar data showed that most of the Venus highlands exhibit a single reduction in radar emissivity values at high altitudes, above 6,053 km (Klose et al., 1992; Pettengill et al., 1992). This decline in radar emissivity with altitude is ascribed to the presence of minerals with a high dielectric constant produced by chemical weathering reactions between the rocks and the near-surface atmosphere. It is expected from theory that materials with high dielectric constants will enhance their radar reflectivity and lower their radar emissivity (Campbell, 1994; Pettengill et al., 1992). Proposed minerals include: (1) pyrite produced through sulfidation and/or oxidation of iron (

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