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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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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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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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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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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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CfA Colloquium: Understanding Haze Formation in Planetary Atmospheres: Lessons From the Lab

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Life 'not as we know it' possible on Saturn's moon Titan

Liquid water is a requirement for life on Earth. But in other, much colder worlds, life might exist beyond the bounds of water-based chemistry.
Taking a simultaneously imaginative and rigidly scientific view, Cornell chemical engineers and astronomers offer a template for life that could thrive in a harsh, cold world - specifically Titan, the giant moon of Saturn.

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Title: Ethyl cyanide on Titan: Spectroscopic detection and mapping using ALMA
Author: M. A. Cordiner, M. Y. Palmer, C. A. Nixon, P. G. J. Irwin, N. A. Teanby, S. B. Charnley, M. J. Mumma, Z. Kisiel, J. Serigano, Y.-J. Kuan, Y.-L. Chuang, K.-S. Wang

We report the first spectroscopic detection of ethyl cyanide (C2H5CN) in Titan's atmosphere, obtained using spectrally and spatially resolved observations of multiple emission lines with the Atacama Large Millimeter/submillimeter array (ALMA). The presence of C2H5CN in Titan's ionosphere was previously inferred from Cassini ion mass spectrometry measurements of C2H5CNH+. Here we report the detection of 27 rotational lines from C2H5CN (in 19 separate emission features detected at >3sigma  confidence), in the frequency range 222-241 GHz. Simultaneous detections of multiple emission lines from CH3N, CH3CN and CH3CCH were also obtained. In contrast to HC3N, CH3CN and CH3CCH, which peak in Titan's northern (spring) hemisphere, the emission from C2H5CN is found to be concentrated in the southern (autumn) hemisphere, suggesting a distinctly different chemistry for this species, consistent with a relatively short chemical lifetime for C2H5CN. Radiative transfer models show that most of the C2H5CN is concentrated at altitudes 300-600 km, suggesting production predominantly in the mesosphere and above. Vertical column densities are found to be in the range (2-5)x1014 cm-2.

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Winter is coming... to Titan's south pole

Gigantic polar clouds of hydrogen cyanide roughly four times the area of the UK are part of the impressive atmospheric diversity of Titan, the largest moon of Saturn, a new study led by Leiden Observatory, the Netherlands Institute for Space Research and the University of Bristol has found. The research is published today in Nature.
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