Candidate regions on titan as promising landing sites for future in situ missions

The highly successful and still on-going Cassini-Huygens mission to the Saturnian system points to the need for a return mission, with both remote and in situ instrumentation. The surface of Saturn’s moon Titan, hosts a complex environment in which many processes occur shaping its landscape. Several of its geological features resemble terrestrial ones, albeit constructed from different material and reflecting the interiorsurface-atmosphere exchanges. The resulting observed morphotectonic features and cryovolcanic candidate regions could benefit from further extensive exploration by a return mission that would focus on these aspects with adapted state-of-the-art instrumentation affording higher spectral and spatial resolution and in situ capabilities. We suggest that some features on Titan are more promising candidate locations for future landing and we present the case for Tui Regio, Hotei Regio and Sotra Patera as to why they could provide a wealth of new scientific results

Potentially active regions on Titan: New processing of Cassini/VIMS data

The Cassini Visual and Infrared Mapping Spectrometer (VIMS) obtained data of Titan's surface from flybys performed during the last seven years. In the 0.8-5.2 µm range, these spectro-imaging data showed that the surface consists of a multivariable geological terrain hosting complex geological processes. The data from the seven narrow methane spectral "windows" centered at 0.93, 1.08, 1.27, 1.59, 2.03, 2.8 and 5 µm provide some information on the lower atmospheric context and the surface parameters that we want to determine. Atmospheric scattering and absorption need to be clearly evaluated before we can extract the surface properties. We apply here a statistical method [1, 2] and a radiative transfer method [3, 1] on three potentially "active" regions on Titan, i.e. regions possibly subject to change over time (in brightness and/or in color etc) [4]: Tui Regio (20°S, 130°W) [5], a 1,500-km long flow-like figure, Hotei Regio (26°S, 78°W) [6], a 700-km wide volcanic-like terrain, and Sotra Facula (15°S, 42°W) [7], a 235-km in diameter area. With our method of Principal Component Analysis (PCA) we have managed to isolate specific regions of distinct and diverse chemical composition. We have tested this method on the previously studied Sinlap crater [8], delimitating compositional heterogeneous areas compatible with the published conclusions by Le Mouélic et al. (2008). Our follow-up method focuses on retrieving the surface albedo of the three areas and of the surrounding terrains with different spectral response by applying a radiative transfer (RT) code. We have used as input most of the Cassini HASI and DISR measurements, as well as new methane absorption coefficients [9], which are important to evaluate the atmospheric contribution and to allow us to better constrain the real surface alterations, by comparing the spectra of these regions. By superposing these results onto the PCA maps, we can correlate composition and morphology. As a test case, we used our RT code to verify the varying brightness of Hotei Regio reported by other investigators based on models lacking proper simulation of the atmospheric absorption [10]. Even though we have used exactly the same dataset, we did not detect any significant surface albedo variations over time; this led us to revise the definition of "active" regions: even if these regions have not visually changed over the course of the Cassini mission, the determination of the chemical composition and the correlation with the morphological structures [11] observed in these areas do not rule out that past and/or ongoing cryovolcanic processes are still a possible interpretation. [1] Solomonidou, A. et al. (2011). Potentially active regions on Titan: New processing of Cassini/VIMS data. In preparation. [2] Stephan, K. et al. (2008). Reduction of instrument-dependent noise in hyperspectral image data using the principal component analysis: Applications to Galileo NIMS data. Planetary and Space Science 56, 406-419. [3] Hirtzig, M. et al. (2011). Applications of a new methane linelist to Cassini/VIMS spectra of Titan in the 1.28-5.2 µm range . In preparation. [4] Wall, s. D. et al. (2009). Cassini RADAR images at Hotei Arcus and western Xanadu, Titan: Evidence for geologically recent cryovolcanic activity. Journal of Geophysical Research 36, L04203, [5] Barnes, J.W. et al. (2006). Cassini observations of flow-like features in western Tui Regio, Titan. Geophysical Research Letters 33, L16204. [6] Soderblom, L.A. et al. (2009). The geology of Hotei Regio, Titan: Correlation of Cassini VIMS and RADAR. Icarus 204, 610-618. [7] Lopes, R.M.C. et al. (2010). Distribution and interplay of geologic processes on Titan from Cassini radar data. Icarus 205, 540-558. [8] Le Mouélic et al. (2008). Mapping and interpretation of Sinlap crater on Titan using Cassini VIMS and RADAR data. Journal of Geophysical Research 113, E04003. [9] Campargue, A. et al. (2011). An empirical line list for methane at 80 K and 296 K in the 1.26-1.71 µm region for planetary investigations. Application to Titan. Icarus. Submitted. [10] Nelson, R. et al (2009). Saturn's Titan: Surface change, ammonia, and implications for atmospheric and tectonic activity. Icarus 199, 429-441. [11] Solomonidou, A. et al. (2011). Possible morphotectonic features on Titan and their origin. Planetary and Space Science. Submitted

Surface albedo changes with time on Titan’s possible cryovolcanic sites: Cassini/VIMS processing and geophysical implications

We present a study on Titan’s possibly cryovolcanic and varying regions as suggested from previous studies [e.g. 1;2;7]. These regions, which are potentially subject to change over time in brightness and are located close to the equator, are Tui Regio, Hotei Regio, and Sotra Patera. We apply two methods on Cassini/VIMS data in order to retrieve their surface properties and monitor any temporal variations. First, we apply a statistical method, the Principal Component Analysis (PCA) [3;4] where we manage to isolate regions of distinct and diverse chemical composition called ‘Region of interest – RoI’. Then, we focus on retrieving the spectral differences (with respect to the Huygens landing site albedo) among the RoIs by applying a radiative transfer code (RT) [5;3]. Hence, we are able to view the dynamical range and evaluate the differences in surface albedo within the RoIs of the three regions. In addition, using this double procedure, we study the temporal surface variations of the three regions witnessing albedo changes with time for Tui Regio from 2005-2009 (darkening) and Sotra Patera from 2005-2006 (brightening) at all wavelengths [3]. The surface albedo variations and the presence of volcanic-like features within the regions in addition to a recent study [6] that calculates Titan's tidal response are significant indications for the connection of the interior with the cryovolcanic candidate features with implications for the satellite’s astrobiological potential

Singular regional brightening events on Titan as seen by Cassini/VIMS

Titan, the largest satellite of Saturn, is the only satellite in the solar system with a dense atmosphere. The close and continuous observations of Titan by the Cassini spacecraft, in orbit around Saturn since July 2004, bring us evidences that Titan tropo-sphere and low stratosphere experience an exotic, but complete meteorological cycle similar to the Earth hy-drological cycle, with hydrocarbons evaporation, con-densation in clouds, and rainfall. Cassini monitoring campaigns also demonstrate that Titan’s cloud cover-age and climate vary with latitude. Titan’s tropics, with globally weak meteorological activity and widespread dune fields, seem to be slightly more arid than the poles, where extensive and numerous liquid reservoirs and sustained cloud activity were discovered. Only a few tropospheric clouds have been observed at Titan’s tropics during the southern summer [2-4]. As equinox was approaching (in August 2009), they oc-curred more frequently and appeared to grow in strength and size [5-7]

Overview of the coordinated ground-based observations of Titan during the Huygens mission

Coordinated ground-based observations of Titan were performed around or during the Huygens atmospheric probe mission at Titan on 14 January 2005, connecting the momentary in situ observations by the probe with the synoptic coverage provided by continuing ground-based programs. These observations consisted of three different categories: (1) radio telescope tracking of the Huygens signal at 2040 MHz, (2) observations of the atmosphere and surface of Titan, and (3) attempts to observe radiation emitted during the Huygens Probe entry into Titan's atmosphere. The Probe radio signal was successfully acquired by a network of terrestrial telescopes, recovering a vertical profile of wind speed in Titan's atmosphere from 140 km altitude down to the surface. Ground-based observations brought new information on atmosphere and surface properties of the largest Satumian moon. No positive detection of phenomena associated with the Probe entry was reported. This paper reviews all these measurements and highlights the achieved results. The ground-based observations, both radio and optical, are of fundamental imnortance for the interpretatinn of results from the Huygens mission

The evolution of the atmosphere and surface of Titan from Cassini infrared observations

Saturn’s Earth-like satellite Titan has a thick and dense atmosphere consisting of nitrogen (98.4%), methane (1.6%) and trace gases such as hydrocarbons and nitriles [1]. The condensed organics are deposited on the surface and the atmosphere-surface-interior interactions shape the ground. In particular, Titan’s methane cycle, similarly to the Earth’s hydrologic cycle, plays an important role in these exchanges by transporting methane at all layers. By applying our radiative transfer code (ARTT) to Cassini/CIRS data taken during Titan flybys from 2004-2010 and to the 1980 Voyager 1 flyby values inferred from the reanalysis of the Infrared Radiometer Spectrometer (IRIS) spectra, as well as to the intervening ground- and space- based observations (such as with ISO), we study the stratospheric evolution over a Titanian year (V1 encounter Ls=9° was reached in mid-2010)

Optimization Of Fiscal Retrenchment Policies Using A Social Accounting Matrix Multiobjective Linear Programming Model: The Case Of New York State

State finances continued to deteriorate over fiscal 2010, suffering from the cumulative impact of lower revenues, ballooning general fund spending and the general rise in the level of unemployment. The phasing out of the American Recovery and Reinvestment Act is likely to constrain even further the fiscal space of local governments throughout the country, potentially endangering a fragile economic recovery. In order to face rapidly rising budget gaps, forty states enacted mid-year budget cuts totaling $22 billion for FY 2010. The fiscal retrenchment approach to budget policy appears to gain ground amongst embattled states, with governors proposing drastic cuts in their fiscal 2011 executive budgets to meet balance-budget requirements. The legacy of the 1970s tax revolts, having made tax hikes difficult to enact, also contributed to corner states into spending reduction strategies. The study of cutback management has heavily focused on how and why reduction targets are adopted by state executives and legislators, as well as on their subsequent effects on local economies. The literature is however scarce on proposing a framework for efficient structuring of budget cuts at the state level. Stricken by uncertainty, many governors are driven toward across-the-board cuts, treating general fund expenditures as a fungible commodity. With states facing increasingly painful budgetary choices, weighting their implications and analyzing potential alternatives become critical to evaluate prospects for regional economic recoveries. In this dissertation, a Social Accounting Matrix (SAM) Multiobjective Linear Programming (MOLP) model is proposed and applied to the case of New York State. The SAM multipliers provide a powerful instrument to evaluate the short-term impact of austerity measures while linear programming (LP) offers an optimization framework to close efficiently the state's budget gap. Attention focuses on the existence of several conflicting objectives that the decision maker tries to optimize simultaneously. Four procedures are introduced to solve the model: the augmented weighted Tchebycheff method, an elistist genetic algorithm, the weighted sum method and constraint programming. The theoretical framework established in the following chapters as well as its application to the Deficit Reduction Plan proposed by Governor Paterson in fiscal 2009 show promising results. The model indeed converges to a set of Pareto optimal solutions that are by essence, more efficient with respect to growth, employment and labor income than the original plan. It constitutes one of the first practical applications of multiobjective optimization to policy design through a Walrasian general equilibrium framework

Étude de Titan dans l'infrarouge proche par spectro-imagerie couplée a l'optique adaptative.

Titan, Saturn's main satellite, is still a mysterious object, despite the arrival of Cassini/Huygens. Yet we can rely on Adaptive Optics: my work presented herein is based on the 1998-2005 infrared data acquired with imagery (PUEO/CFHT, NACO/VLT), spectroscopy (NACO) or Integral Field Spectrometry (OASIS/WHT). In the 0. 8-2. 0µm spectral range, both the atmosphere and the surface of Titan can be probed down to, in or out of five methane windows. Voyager revealed the asymmetry splitting Titan's atmosphere in two, North and South, because of a local enhancement of aerosols in the winter hemisphere. We could monitor the inversion of this asymmetry, when Titan entered into Southern summer : since 2002, the Northern limb is the brightest. We also describe other subtle features, such as the condensation of aerosols at 80km of altitude during Titan's night; or the complex meteorological system, confined within the 70th parallel, between 18 and 83km, probably made of small deforming clouds, but we still ignore their true nature or origin. We studied Titan's surface by constructing maps at 1. 28, 1. 6 and 2. 0µm, with a stunning similarity to HST or Cassini ones. We also tried to identify the chemical composition of the bright and dark features by means of differential spectroscopy ; water ice is a good candidate as the main constituent of the surface, with either an excess of bright methane/ethane ices, or an excess of dark hydrocarbon liquids. We do not detect any specular reflection, ruling out the existence of large bodies of liquid on the surface : how about a permafrost of liquid ethane within solid water ice as the replenishing source of the atmospheric methaneMalgré l'arrivée de Cassini/Huygens dans le système Saturnien, Titan reste encore bien mystérieux. C'est là que peut intervenir l'Optique Adaptative: les travaux présentés ici reposent sur l'étude des données 1998-2005 acquises en infrarouge proche, par imagerie (PUEO/CFHT, NACO/VLT), spectroscopie (NACO) et spectroscopie à intégrale de champ (OASIS/WHT). La gamme spectrale couverte permet de sonder la basse atmosphère de Titan, mais aussi d'atteindre sa surface dans cinq fenêtres du méthane, entre 0,8 et 2,0µm. Depuis Voyager, l'atmosphère de Titan est connue pour son asymétrie Nord-Sud, due à un excès d'aérosols dans l'hémisphère d'hiver. Nous avons suivi l'inversion de cette asymétrie, lorsqu'a débuté l'été Sud, estimant la transition vers 2002 : le limbe Nord prédomine désormais. D'autres motifs plus subtils sont également décrits, comme la condensation nocturne des aérosols, vers 80km d'altitude; ou encore le système météorologique en constante déformation en deçà du 70eme parallèle, localisé entre 18 et 83km, probablement constitué de nuages, mais dont nous ignorons la nature et l'origine. Quant à la surface de Titan, des cartes ont été réalisées à 1,28, 1,6 et 2,0µm, avec une excellente similitude par rapport aux cartes HST ou Cassini. Nous avons tenté d'identifier la composition chimique des régions claires et sombres, par spectroscopie différentielle : le constituant commun semble être la glace d'eau, avec un excès local de glaces de méthane/éthane brillantes, ou d'hydrocarbures liquides sombres. Puisque nos images ne révèlent aucune réflexion spéculaire, donc aucune étendue liquide, les zones sombres cacheraient-elles en sous-sol un réservoir de méthane