Spectral properties of Titan's impact craters imply chemical weathering of its surface

Neish, C. D.; Barnes, J. W.; Sotin, C.; MacKenzie, Shannon; Soderblom, Jason M.; Mouëlic, Stéphane Le; Kirk, Randolph L.; Stiles, B.; Malaska, Michael J.; Gall, Alice Le; Brown, R. H.; Baines, K. H.; Buratti, B. J.; Clark, R. N.; Nicholson, P.

doi:10.1002/2015gl063824

Cited by 40 publications

(32 citation statements)

References 52 publications

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“…Atmospheric material may have subsequently covered them again. This would provide a spectral coating consistent with a mixture of organic materials and water ice in impact craters, as suggested by Neish et al (). Below this covering, the emissivity is consistent with water ice materials (Janssen et al, ; Malaska et al, ).…”

Section: Discussion: Implications and Interpretationssupporting

confidence: 54%

“…Selected regions of interest extracted from the major geomorphological units on Titan shown on a Cassini Visual and Infrared Mapping Spectrometer mosaic map at 2.03 μm. The characterization of the regions is based on morphological characteristics from studies by Lopes et al (, ), Malaska et al (, ), Neish et al (), and Radebaugh et al (). The basemap corresponds to a 2.03 μm global map of Ta to T114 flybys (Le Mouélic et al, , ).…”

Section: Context and Observationsmentioning

confidence: 99%

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

et al. 2018

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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.

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Section: Discussion: Implications and Interpretationssupporting

confidence: 54%

Section: Context and Observationsmentioning

confidence: 99%

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

et al. 2018

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“…The sediments that accumulated on the seafloor of these basins are then presumed to contain components of both organic atmospheric products and water-ice sediment that was eroded from the surrounding landscape. A terrain composed of both water-ice sediments and organic components was also postulated by Neish et al (2015) to explain the spectral character of impact craters. In this model, the mountainous terrains (Mtn and Vd b ) represent regions where this primordial bedrock remains exposed, either never having been submerged below an ocean or recently exhumed.…”

Section: Stage 1 -Build-up Of Large Sedimentary Deposits and A Polar Oceanmentioning

confidence: 99%

Geomorphologic mapping of titan's polar terrains: Constraining surface processes and landscape evolution

Birch

Hayes

Dietrich

et al. 2017

Icarus

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We present a geomorphologic map of Titan's polar terrains. The map was generated from a combination of Cassini Synthetic Aperture Radar (SAR) and Imaging Science Subsystem imaging products, as well as altimetry, SARTopo and radargrammetry topographic datasets. In combining imagery with topographic data, our geomorphologic map reveals a stratigraphic sequence from which we infer process interactions between units. In mapping both polar regions with the same geomorphologic units, we conclude that processes that formed the terrains of the north polar region also acted to form the landscape we observe at the south. Uniform, SAR-dark plains are interpreted as sedimentary deposits, and are bounded by moderately dissected uplands. These plains contain the highest density of filled and empty lake depressions, and canyons. These units unconformably overlay a basement rock that outcrops as mountains and SAR-bright dissected terrains at various elevations across both poles. All these units are then superposed by surficial units that slope towards the seas, suggestive of subsequent overland transport of sediment. From estimates of the depths of the embedded empty depressions and canyons that drain into the seas, the SAR-dark plains must be >600 m thick in places, though the thickness may vary across the poles. At the lowest elevations of each polar region, there are large seas, which are currently liquid methane/ethane filled at the north and empty at the south. The large plains deposits and the surrounding hillslopes may represent remnant landforms that are a result of previously vast polar oceans, where larger liquid bodies may have allowed for a sustained accumulation of soluble and insoluble sediments, potentially forming layered sedimentary deposits. Coupled with vertical crustal movements, the resulting layers would be of varying solubilities and erosional resistances, allowing formation of the complex landscape that we observe today.

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“…Other units include “dark brown,” which seems to be dominated by dunes, and “dark blue,” which seems to be richer in water ice than the dark brown unit [ Barnes et al , ]. Neish et al [] examined the spectra of Titan's craters as a function of degradation state and concluded that impacts expose water ice and organics and then rainfall removes the soluble organics, leaving behind water ice and insoluble organics.…”

Section: Connection With the Surfacementioning

confidence: 99%

Titan's atmosphere and climate

2017

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Titan is the only moon with a substantial atmosphere, the only other thick N2 atmosphere besides Earth's, the site of extraordinarily complex atmospheric chemistry that far surpasses any other solar system atmosphere, and the only other solar system body with stable liquid currently on its surface. The connection between Titan's surface and atmosphere is also unique in our solar system; atmospheric chemistry produces materials that are deposited on the surface and subsequently altered by surface‐atmosphere interactions such as aeolian and fluvial processes resulting in the formation of extensive dune fields and expansive lakes and seas. Titan's atmosphere is favorable for organic haze formation, which combined with the presence of some oxygen‐bearing molecules indicates that Titan's atmosphere may produce molecules of prebiotic interest. The combination of organics and liquid, in the form of water in a subsurface ocean and methane/ethane in the surface lakes and seas, means that Titan may be the ideal place in the solar system to test ideas about habitability, prebiotic chemistry, and the ubiquity and diversity of life in the universe. The Cassini‐Huygens mission to the Saturn system has provided a wealth of new information allowing for study of Titan as a complex system. Here I review our current understanding of Titan's atmosphere and climate forged from the powerful combination of Earth‐based observations, remote sensing and in situ spacecraft measurements, laboratory experiments, and models. I conclude with some of our remaining unanswered questions as the incredible era of exploration with Cassini‐Huygens comes to an end.

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Spectral properties of Titan's impact craters imply chemical weathering of its surface

Cited by 40 publications

References 52 publications

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

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

Geomorphologic mapping of titan's polar terrains: Constraining surface processes and landscape evolution

Titan's atmosphere and climate

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