Anezina Solomonidou

Surface albedo spectral properties of geologically interesting areas on Titan

We investigate the nature and possible formation processes of three areas on Titans surface which have been suggested as geologically interesting: Hotei Regio, Tui Regio, and Sotra Patera. We also reanalyze the spectral characteristics of the Huygens Landing Site. We apply a statistical Principal Component Analysis (PCA) and a radiative transfer (RT) method on the Visual and Infrared Mapping Spectrometer Datacubes in order to retrieve the surface albedo of distinct spectral units in the near infrared. We have been able to exploit only a subset of the currently available Hotei Regio data, which are, in general, not optimal in terms of geometry for an analysis with a plane-parallel RT code. Our inferred surface albedos present generally higher values from 1 to 2 µm and lower ones at 0.94 and in the 2.6–5 µm region. The Regions of Interest (RoIs) within Hotei Regio, Tui Regio, and Sotra Patera are always significantly brighter than the surrounding areas. The largest variations are found longward of 2 µm and mainly at 5 µm. This higher surface albedo with respect to the surrounding area and, in general, the fact that the spectral behavior is different for each of these areas, is probably indicative of diverse chemical compositions and origins. We compare the spectral albedos with some suggested surface candidates on Titan (such as H2O, CO2, and CH4 ices, as well as tholin) and discuss possible chemical composition variations as well as other interpretations.

Structural and tidal models of Titan and inferences on cryovolcanism

Titan, Saturns largest satellite, is subject to solid body tides exerted by Saturn on the timescale of its orbital period. The tide-induced internal redistribution of mass results in tidal stress variations, which could play a major role for Titans geologic surface record. We construct models of Titans interior that are consistent with the satellites mean density, polar moment-of-inertia factor, obliquity, and tidal potential Love number k2 as derived from Cassini observations of Titans low-degree gravity field and rotational state. In the presence of a global liquid reservoir, the tidal gravity field is found to be consistent with a subsurface water-ammonia ocean more than 180 km thick and overlain by an outer ice shell of less than 110 km thickness. The model calculations suggest comparatively low ocean ammonia contents of less than 5 wt % and ocean temperatures in excess of 255 K, i.e., higher than previously thought, thereby substantially increasing Titans potential for habitable locations. The calculated diurnal tidal stresses at Titans surface amount to 20 kPa, almost comparable to those expected at Enceladus and Europa. Tidal shear stresses are concentrated in the polar areas, while tensile stresses predominate in the near-equatorial, midlatitude areas of the sub- and anti-Saturnian hemispheres. The characteristic pattern of maximum diurnal tidal stresses is largely compliant with the distribution of active regions such as cryovolcanic candidate areas. The latter could be important for Titans habitability since those may provide possible pathways for liquid water-ammonia outbursts on the surface and the release of methane in the satellites atmosphere.

The Spectral Nature of Titan's Major Geomorphological Units: Constraints on Surface Composition

We investigate Titans low- and mid-latitude surface using spectro-imaging near-infrared data from Cassini/VIMS. 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 VIMS 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 Titans complex surface. Our results show a latitudinal dependence of Titans surface composition, with water ice being the major constituent at latitudes beyond 30°N and 30°S, while Titans 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 Titans surface and, by implication, its interior. We discuss our results in terms of origin and evolution theories.

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

In 13 years, infrared observations from the Visual and Infrared Mapping Spectrometer onboard Cassini provided significant hints about the spectral and geological diversity of Titans surface. The analysis of the infrared (IR) signature of spectral units enables constraining the surface composition, which is crucial for understanding possible interactions between Titans interior, surface, and atmosphere. Here we investigate a selection of areas in the equatorial regions, imaged by Cassinis 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 Titans 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.

Planetary geological processes

In this introduction to planetary geology, we review the major geologic processes affecting the solid bodies of the solar system, namely volcanism, tectonism, impact cratering, and erosion. We illustrate the interplay of these processes in different worlds, briefly reviewing how they affect the surfaces of the Earths Moon, Mercury, Venus and Mars, then focusing on two very different worlds: Jupiters moon Io, the most volcanically active object in the solar system, and Saturns moon Titan, where the interaction between a dense atmosphere and the surface make for remarkably earth-like landscapes despite the great differences in surface temperature and composition.