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TOPIC: Titan
Blobrana


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RE: Titan
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Title: Titan organic aerosols: molecular composition and structure of laboratory analogues inferred from systematic pyrolysis gas chromatography mass spectrometry analysis
Author: Marietta Morissona, Cyril Szopa, Nathalie Carrasco, Arnaud Buch, Thomas Gautier

Numerous studies have been carried out to characterize the chemical composition of laboratory analogues of Titan aerosols (tholins), but their molecular composition as well as their structure are still poorly known. If pyrolysis gas chromatography mass spectrometry (pyr-GCMS) has been used for years to give clues about this composition, the highly disparate results obtained can be attributed to the analytical conditions used and/or to differences in the nature of the analogues studied. In order to have a better description of Titan tholins molecular composition, we led a systematic analysis of these materials using pyr-GCMS with two major objectives: (i) exploring the analytical parameters to estimate the biases this technique can induce and to find an optimum for analyses allowing the detection of a wide range of compounds and thus a characterization of the tholins composition as comprehensive as possible, and (ii) highlighting the role of the CH4 ratio in the gaseous reactive medium on the tholins molecular structure. With this aim, we used a radio-frequency plasma discharge to synthesize tholins with different concentrations of CH4 diluted in N2. The samples were systematically pyrolyzed from 200 to 600°C. The extracted gases were then analysed by GCMS for their molecular identification.

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Blobrana


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Title: Titan brighter at twilight than in daylight
Author: Antonio García Muñoz, Panayotis Lavvas, Robert A. West

Investigating the overall brightness of planets (and moons) provides insight into their envelopes and energy budgets [1, 2, 3, 4]. Titan phase curves (a representation of overall brightness vs. Sun-object-observer phase angle) have been published over a limited range of phase angles and spectral passbands [5, 6]. Such information has been key to the study of the stratification, microphysics and aggregate nature of Titan's atmospheric haze [7, 8], and has complemented the spatially-resolved observations first showing that the haze scatters efficiently in the forward direction [7, 9]. Here we present Cassini Imaging Science Subsystem whole-disk brightness measurements of Titan from ultraviolet to near-infrared wavelengths. The observations reveal that Titan's twilight (loosely defined as the view when the phase angle 150deg) outshines its daylight at various wavelengths. From the match between measurements and models, we show that at even larger phase angles the back-illuminated moon will appear much brighter than when fully illuminated. This behaviour is unique to Titan in our solar system, and is caused by its extended atmosphere and the efficient forward scattering of sunlight by its atmospheric haze. We infer a solar energy deposition rate (for a solar constant of 14.9 Wm-2) of (2.84±0.11)x10^14 W, consistent to within 1-2 standard deviations with Titan's time-varying thermal emission spanning 2007- 2013 [10, 11]. We propose that a forward scattering signature may also occur at large phase angles in the brightness of exoplanets with extended hazy atmospheres, and that this signature has valuable diagnostic potential for atmospheric characterization.

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Blobrana


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Titan's Detached Haze Layer
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Title: Aerosols optical properties in Titan's Detached Haze Layer before the equinox
Author: Benoît Seignovert, Pascal Rannou, Panayotis Lavvas, Thibaud Cours, Robert A. West

UV observations with Cassini ISS Narrow Angle Camera of Titan's detached haze is an excellent tool to probe its aerosols content without being affected by the gas or the multiple scattering. Unfortunately, its low extent in altitude requires a high resolution calibration and limits the number of images available in the Cassini dataset. However, we show that it is possible to extract on each profile the local maximum of intensity of this layer and confirm its stability at 500±8 km during the 2005-2007 period for all latitudes lower than 45°N. Using the fractal aggregate scattering model of Tomasko et al. (2008) and a single scattering radiative transfer model, it is possible to derive the optical properties required to explain the observations made at different phase angles. Our results indicates that the aerosols have at least ten monomers of 60 nm radius, while the typical tangential column number density is about 2 x 10^10 agg.m^-2. Moreover, we demonstrate that these properties are constant within the error bars in the southern hemisphere of Titan over the observed time period. In the northern hemisphere, the size of the aerosols tend to decrease relatively to the southern hemisphere and are associated with a higher tangential opacity. However, the lower number of observations available in this region due to the orbital constraints is a limiting factor in the accuracy of these results. Assuming a fixed homogeneous content we notice that the tangential opacity can fluctuate up to a factor 3 among the observations at the equator. These variations could be linked with short scale temporal and/or longitudinal events changing the local density of the layer.

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Blobrana


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Titan's dunes
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Electrified sand could explain Titan's odd backward-facing dunes

Static electricity clumping up sand could explain the strange dunes on Saturn' largest moon.
Titan is a hazy moon with a thick, orange nitrogen atmosphere. Its poles are home to placid methane lakes, and its equatorial regions are covered with dunes up to 100 metres high.
The dunes seem to be facing in the wrong direction, though. The prevailing winds on Titan blow toward the west, but the dunes point east. "You've got this apparent paradox," says Josef Dufek at the Georgia Institute of Technology in Atlanta. "The winds are moving one way and the sediments are moving the other way." 
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Blobrana


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Title: Titan's Atmosphere and Climate
Author: Sarah M. Hörst

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 favourable 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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Blobrana


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NASA Scientists Find 'Impossible' Cloud on Titan - Again

The puzzling appearance of an ice cloud seemingly out of thin air has prompted NASA scientists to suggest that a different process than previously thought -- possibly similar to one seen over Earth's poles -- could be forming clouds on Saturn's moon Titan.
Located in Titan's stratosphere, the cloud is made of a compound of carbon and nitrogen known as dicyanoacetylene (C4N2), an ingredient in the chemical ****tail that colors the giant moon's hazy, brownish-orange atmosphere.
Scientists from NASA's Cassini mission think the appearance of a cloud of dicyanoacetylene (C4N2) ice in Titans stratosphere is explained by "solid-state" chemistry taking place inside ice particles. The particles have an inner layer of cyanoacetylene (HC3N) ice coated with an outer layer of hydrogen cyanide (HCN) ice. (Left) When a photon of light penetrates the outer shell, it can interact with the HC3N, producing C3N and H. (Center) The C3N then reacts with HCN to yield (right) C4N2 and H. Another reaction that also yields C4N2 ice and H also is possible, but less likely. 
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Blobrana


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Methane-flooded canyons on Titan

The aptly named Titan, Saturn's largest moon, is remarkably Earth-like. Its diameter is only about 40% that of our planet, but Titan's nitrogen-rich, dense atmosphere and the geological activity at the moon's surface make comparisons between the two bodies inevitable.
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Blobrana


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Titan's Dunes and Other Features Emerge in New Images

New scenes from a frigid alien landscape are coming to light in recent radar images of Saturn's largest moon, Titan, from NASA's Cassini spacecraft.
Cassini obtained the views during a close flyby of Titan on July 25, when the spacecraft came as close as 976 kilometers from the giant moon. The spacecraft's radar instrument is able to penetrate the dense, global haze that surrounds Titan, to reveal fine details on the surface.
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Dissolving Titan

Saturn's moon Titan is home to seas and lakes filled with liquid hydrocarbons, but what makes the depressions they lie in? A new study suggests that the moon's surface dissolves in a similar process that creates sinkholes on Earth.
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Blobrana


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Title: Dissolution on Titan and on Earth: Towards the age of Titan's karstic landscapes
Author: Thomas Cornet, Daniel Cordier, Tangui Le Bahers, Olivier Bourgeois, Cyril Fleurant, Stéphane Le Mouélic, Nicolas Altobelli

Titan's polar surface is dotted with hundreds of lacustrine depressions. Based on the hypothesis that they are karstic in origin, we aim at determining the efficiency of surface dissolution as a landshaping process on Titan, in a comparative planetology perspective with the Earth as reference. Our approach is based on the calculation of solutional denudation rates and allow inference of formation timescales for topographic depressions developed by chemical erosion on both planetary bodies. The model depends on the solubility of solids in liquids, the density of solids and liquids, and the average annual net rainfall rates. We compute and compare the denudation rates of pure solid organics in liquid hydrocarbons and of minerals in liquid water over Titan and Earth timescales. We then investigate the denudation rates of a superficial organic layer in liquid methane over one Titan year. At this timescale, such a layer on Titan would behave like salts or carbonates on Earth depending on its composition, which means that dissolution processes would likely occur but would be 30 times slower on Titan compared to the Earth due to the seasonality of precipitation. Assuming an average depth of 100 m for Titan's lacustrine depressions, these could have developed in a few tens of millions of years at polar latitudes higher than 70{\deg} N and S, and a few hundreds of million years at lower polar latitudes. The ages determined are consistent with the youth of the surface (<1 Gyr) and the repartition of dissolution-related landforms on Titan.

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