Scale Model of Titan Maritime Explorer (TiME) Tested in Chile

Onboard Science Insights and Vehicle Dynamics from Scale-Model Trials of the Titan Mare Explorer (TiME) Capsule at Laguna Negra, Chile

Author:

Lorenz

Abstract:

A scale model of the proposed Titan Mare Explorer capsule was deployed at the Planetary Lake Lander field site at Laguna Negra, Chile. The tests served to calibrate models of wind-driven drift of the capsule and to understand its attitude motion in the wave field, as well as to identify dynamic and acoustic signatures of shoreline approach. This information enables formulation of onboard trigger criteria for near-shore science data acquisition.

The Intriguing Active Drainage System Into Titan's Ligeia Mare

Liquid-filled canyons on Titan

Authors:

Poggiali et al

Abstract:

In May 2013 the Cassini RADAR altimeter observed channels in Vid Flumina, a drainage network connected to Titan's second largest hydrocarbon sea, Ligeia Mare. Analysis of these altimeter echoes shows that the channels are located in deep (up to ~570 m), steep-sided, canyons and have strong specular surface reflections that indicate they are currently liquid filled. Elevations of the liquid in these channels are at the same level as Ligeia Mare to within a vertical precision of about 0.7 m, consistent with the interpretation of drowned river valleys. Specular reflections are also observed in lower order tributaries elevated above the level of Ligeia Mare, consistent with drainage feeding into the main channel system.

NASA Begins Researching Submarine for Icy Moons of the Solar System

One of the most profound and exciting breakthroughs in planetary science in the last two decades has been the discovery of liquid methane lakes on the surface of Saturn’s largest moon Titan, and liquid oceans under the icy surfaces of many of the giant gas planets’ other moons. Thrillingly, these some of these “waters” may actually harbor life.

Unfortunately, we don’t know much about them. Probes such as Juno and Cassini can only get so close. Also, subsurface oceans can only be sensed indirectly. The European Space Agency’s Huygens probe did land on Titan in 2005, but on a solid surface rather than on liquid. So how can we explore these seas?

An exciting idea being explored is developing submarines to send through space to the moons. Over the next two years, NASA is devoting half a million dollars to researching the prospect of sending such a vehicle to Titan. But there are other studies out there, too – with targets including Jupiter’s Europa and Ganymede, and Saturn’s Enceladus. But are such missions actually within our technological reach?

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Titan has Numerous Methane Filled Canyons

Liquid methane-filled canyons hundreds of meters deep with walls as steep as ski slopes etch the surface of Titan, researchers report in a new study. The new findings provide the first direct evidence of these features on Saturn's largest moon, and could give scientists insights into Titan's origins and similar geologic processes on Earth, according to the study's authors.

New Cassini radar observations of Titan's north pole depict cavernous gorges a little less than a kilome-ter (less than half a mile) wide with walls up to 570 meters (1870 feet) tall -- about 30 meters (98 feet) higher than New York's Freedom Tower. The eight canyons branch off from Vid Flumina, a more than 400-kilometer (249-mile) long river flowing into Titan's second-largest sea, Ligeia Mare. The new data confirm the canyons are filled with flowing methane -- a feature researchers had suspected but not directly observed, according to the study's authors.

The new findings suggest the canyons were likely carved by liquid methane draining into Vid Flumina, a process similar to the carving of river gorges on Earth, according to the study's authors. The new re-search could help scientists better understand these geological processes, they said.

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Titan's Kraken Mare Should NOT be There

The influence of subsurface flow on lake formation and north polar lake distribution on Titan

Authors:

Horvath et al

Abstract:

Observations of lakes, fluvial dissection of the surface, rapid variations in cloud cover, and lake shoreline changes indicate that Saturn's moon Titan is hydrologically active, with a hydrocarbon-based hydrological cycle dominated by liquid methane. Here we use a numerical model to investigate the Titan hydrological cycle – including surface, subsurface, and atmospheric components – in order to investigate the underlying causes of the observed distribution and sizes of lakes in the north polar region. The hydrocarbon-based hydrological cycle is modeled using a numerical subsurface flow model and analytical runoff scheme, driven by a general circulation model with an active methane-cycle. This model is run on synthetically generated topography that matches the fractal character of the observed topography, without explicit representation of the effects of erosion and deposition. At the scale of individual basins, intermediate to high permeability (10−8–10−6 cm2) aquifers are required to reproduce the observed large stable lakes. However, at the scale of the entire north polar lake district, a high permeability aquifer results in the rapid flushing of methane through the aquifer from high polar latitudes to dry lower polar latitudes, where methane is removed by evaporation, preventing large lakes from forming. In contrast, an intermediate permeability aquifer slows the subsurface flow from high polar latitudes, allowing greater lake areas. The observed distribution of lakes is best matched by either a uniform intermediate permeability aquifer, or a combination of a high permeability cap at high latitudes surrounded by an intermediate permeability aquifer at lower latitudes, as could arise due to karstic processes at the north pole. The stability of Kraken Mare further requires reduction of the evaporation rate over the sea to 1% of the value predicted by the general circulation model, likely as a result of dissolved ethane, nitrogen, or organic solutes, and/or a climatic lake effect. These results reveal that subsurface flow through aquifers plays an important role in Titan's hydrological cycle, and exerts a strong influence over the distribution, size, and volatile budgets of Titan's lakes.

What Lies Beneath Titan's Seas?

Back when Cassini was approaching Saturn and we all anticipated the arrival of the Huygens payload on the surface, speculation grew that rather than finding a solid surface, Huygens might ‘splash down’ in a hydrocarbon sea. I can remember art to that effect in various Internet venues of the time. In the event, Huygens came down on hard terrain, but since then Cassini’s continuing surveys have shown that seas and lakes do exist on the moon. Over 1.6 million square kilometers (about two percent of the surface of Titan) are covered in liquid.

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Measuring the Speed of Sound in Titan's Seas Might Reveal Their Composition

How speed of sound measurements could bring constraints on the composition of Titan's seas

Author:

Cordier

Abstract:

The hydrocarbons seas of Titan, discovered by Cassini/Huygens mission are among the most mysterious and interesting features of this moon. In the future, a possible dedicated planetary probe, will certainly measure the speed of sound in this cryogenic liquid, as it was planned in the case of a Huygens landing into a sea. Previous theoretical studies of such acoustic measurements were based on rather simple models, leading in some cases to unphysical situations. Employed in a vast body of chemical engineering works, the state of the art PC-SAFT model has been recently introduced in studies aimed at Titan. Here, I revisit the issue of the speed of sound in Titan's liquids, in the light of this theory. I describe, in detail, the derivation of the speed of sound from the chosen equation of state and the potential limitations of the approach. To make estimations of the composition of a ternary liquid mixture N2:CH4:C2H6 from speed of sound measurements an original inversion algorithm is proposed. It is shown that 50 measures between 90 K and 100 K are enough to ensure an accuracy of the derived compositions better than 10%. The influence of the possible presence of propane is also investigated.

The "Magic Islands" of Titan's Ligeia Mare are Probably Large Waves

Titan’s “Magic Islands”: Transient features in a hydrocarbon sea

Authors:

Hofgartner et al

Abstract:

The region of Titan’s hydrocarbon sea, Ligeia Mare, where transient bright features were previously discovered, was anomalously bright in the first of two more recent Cassini RADAR observations but not the second. Another transient bright feature in a different region of Ligeia Mare was also discovered in the first of the new observations. Here we present all the high-resolution observations of the regions containing these transient features and the quantitative constraints that we derived from them. We argue that these features are unlikely to be SAR image artifacts or permanent geophysical structures and thus their appearance is the result of ephemeral phenomena on Titan. We find that the transient features are more consistent with floating and/or suspended solids, bubbles, and waves than tides, sea level change, or seafloor change and based on the frequency of these phenomena in terrestrial settings, we consider waves to be the most probable hypothesis. These transient features are the first instance of active processes in Titan’s lakes and seas to be confirmed by multiple detections and demonstrate that Titan’s seas are not stagnant but rather dynamic environments.

Circulation in Titan’s seas may be Driven by the Sun and Methane Precipitation

Sun-stirred Kraken Mare: Circulation in Titan’s seas induced by solar heating and methane precipitation

Authors:

Tokano et al

Abstract:

Density-driven circulation in Titan’s seas forced by solar heating and methane evaporation/precipitation is simulated by an ocean circulation model. If the sea is transparent to sunlight, solar heating can induce anti-clockwise gyres near the sea surface and clockwise gyres near the sea bottom. The gyres are in geostrophic balance between the radially symmetric pressure gradient force and Coriolis force. If instead the sea is turbid and most sunlight is absorbed near the sea surface, the sea gets stratified in warm seasons and the circulation remains weak. Precipitation causes compositional stratification of the sea to an extent that the sea surface temperature can be lower than the sea interior temperature without causing a convective overturning. Non-uniform precipitation can also generate a latitudinal gradient in the methane mole fraction and density, which drives a meridional overturning with equatorward currents near the sea surface and poleward currents near the sea bottom. However, gyres are more ubiquitous than meridional overturning.

How Titans Fluids Might Influence its Tectonic Evolution

Role of fluids in the tectonic evolution of Titan

Authors:

Yung-Chun Liu et al

Abstract:

Detailed analyses of slopes and arcuate planform morphologies of Titan’s equatorial mountain ridge belts are consistent with formation by contractional tectonism. However, contractional structures in ice require large stresses (4–10 MPa), the sources of which are not likely to exist on Titan. Cassini spacecraft imagery reveals a methane-based hydrological cycle on Titan that likely includes movement of fluids through the subsurface. These crustal liquids may enable contractional tectonic features to form as groundwater has for thrust belts on Earth. In this study, we show that liquid hydrocarbons in Titan’s near subsurface can lead to fluid overpressures that facilitate contractional deformation at smaller stresses (less than 1 MPa) by significantly reducing the shear strength of materials. Titan’s crustal conditions with enhanced pore fluid pressures favor the formation of thrust faults and related folds in a contractional stress field. Thus, surface and near-surface hydrocarbon fluids made stable by a thick atmosphere may play a key role in the tectonic evolution of Titan.

Three of Titan's Seas Have Very Small Waves

Space is mostly vast and empty. So whenever we notice something like ripples on a lake, on the frozen moon of a gas giant, we take notice.

At a meeting of the American Geophysical Union in San Francisco this week, it was reported that Cassini images of Saturn's moon Titan showed light being reflected from the Ligeia Mare, a frigid sea of hydrocarbons on that moon. Subsequent images showed the same phenomenon on two other seas of Titan, as well. These are thought to be waves, the first waves detected anywhere other than Earth, and suggest that Titan has more geophysical activity than previously thought.

Surfers on Earth, known for seeking out remote and secretive locations, shouldn't get too excited. According to mathematical modelling and radar imagery, these waves are only 1.5 cm (0.6 inches) tall, and they're moving only 0.7 metres (2.3 feet) per second. Plus, they're on a sea of liquid hydrocarbons—mostly methane—that is a frigid -180 degrees Celsius (-292 F.)

Planetary scientists are taking note, though, because these waves show that Titan has an active environment, rather than just being a moon frozen in time. It's thought that the change in seasons on Titan is responsible for these waves, as Titan begins its 7 year summer. Processes related to the changing seasons on Titan have created winds, which have cause these ripples.

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Titan's Evaporites are as Varied as on Earth

Compositional Similarities and Distinctions between Titan's Evaporitic Terrains

Authors:

MacKenzie et al

Abstract:

We document the similarities in composition between the equatorial basins Tui Regio, Hotei Regio, and other 5-μm-bright materials, notably the north polar evaporites, by investigating the presence and extent of an absorption feature at 4.92 μm. In most observations, Woytchugga Lacuna, Ontario Lacus, MacKay Lacus, deposits near Fensal, some of the lakes and dry lake beds south of Ligeia, and the southern shores of Kraken Mare share the absorption feature at 4.92 \um observed in the spectra of Tui and Hotei. Besides Woytchugga and at Fensal, these 5-μm-bright deposits are geomorphologically-substantiated evaporites. Thus, the similarity in composition strengthens the hypothesis that Tui and Hotei once contained liquid. Other evaporite deposits, however, do not show the 4.92 \um absorption, notably Muggel Lacus and the shores of Ligeia Mare at the north pole. This difference in composition suggests that there are more than one kind of soluble material in Titan's lakes that can create evaporite and/or that the surface properties at the VIMS wavelength scale are not uniform between the different deposits (crystal size, abundance, etc). Our results indicate that the surface structure, composition, and formation history of Titan's evaporites may be at least as dynamic and complex as their Earth counterparts.

Simulating Titan's Methane Cycle

Simulating Titan’s methane cycle with the TitanWRF General Circulation Model

Authors:

Newman et al

Abstract:

Observations provide increasing evidence of a methane hydrological cycle on Titan. Earth-based and Cassini-based monitoring has produced data on the seasonal variation in cloud activity and location, with clouds being observed at increasingly low latitudes as Titan moved out of southern summer. Lakes are observed at high latitudes, with far larger lakes and greater areal coverage in the northern hemisphere, where some shorelines extend down as far as 50°N. Rainfall at some point in the past is suggested by the pattern of flow features on the surface at the Huygens landing site, while recent rainfall is suggested by surface change. As with the water cycle on Earth, the methane cycle on Titan is both impacted by tropospheric dynamics and likely able to impact this circulation via feedbacks. Here we use the 3D TitanWRF General Circulation Model (GCM) to simulate Titan’s methane cycle. In this initial work we use a simple large-scale condensation scheme with latent heat feedbacks and a finite surface reservoir of methane, and focus on large-scale dynamical interactions between the atmospheric circulation and methane, and how these impact seasonal changes and the long term (steady state) behavior of the methane cycle. We note five major conclusions: (1) Condensation and precipitation in the model is sporadic in nature, with interannual variability in its timing and location, but tends to occur in association with both (a) frequent strong polar upwelling during spring and summer in each hemisphere, and (b) the Inter-Tropical Convergence Zone (ITCZ), a region of increased convergence and upwelling due to the seasonally shifting Hadley cells. (2) An active tropospheric methane cycle affects the stratospheric circulation, slightly weakening the stratospheric superrotation produced. (3) Latent heating feedback strongly influences surface and near-surface temperatures, narrowing the latitudinal range of the ITCZ, and changing the distribution – and generally weakening the strength – of upwelling events. (4) TitanWRF favors low latitude ‘cloudiness’ around northern spring equinox as the ITCZ moves from south to north across the equator, versus the opposite time of year. (5) TitanWRF produces drying of low and mid latitudes with net transport of surface methane to high latitudes, and shows persistent hemispheric asymmetry in the methane cycle such that the favored pole for surface methane is the one with winter occurring closest to perihelion.

The Bathtub Rings of Titan's Evaporites

Structure of Titan's evaporites

Authors:

Cordier et al

Abstract:

Numerous geological features that could be evaporitic in origin have been identified on the surface of Titan. Although they seem to be water-ice poor, their main properties -chemical composition, thickness, stratification- are essentially unknown. In this paper, which follows on a previous one focusing on the surface composition (Cordier et al., 2013), we provide some answers to these questions derived from a new model. This model, based on the up-to-date thermodynamic theory known as "PC-SAFT", has been validated with available laboratory measurements and specifically developed for our purpose. 1-D models confirm the possibility of an acetylene and/or butane enriched central layer of evaporitic deposit. The estimated thickness of this acetylene-butane layer could explain the strong RADAR brightness of the evaporites. The 2-D computations indicate an accumulation of poorly soluble species at the deposit's margin. Among these species, HCN or aerosols similar to tholins could play a dominant role. Our model predicts the existence of chemically trimodal "bathtub rings" which is consistent with what it is observed at the south polar lake Ontario Lacus. This work also provides plausible explanations to the lack of evaporites in the south polar region and to the high radar reflectivity of dry lakebeds.

What Kind of Life Could Evolve on Titan?

Could there be life on Saturn’s large moon Titan? Asking the question forces astrobiologists and chemists to think carefully and creatively about the chemistry of life, and how it might be different on other worlds than it is on Earth. In February, a team of researchers from Cornell University, including chemical engineering graduate student James Stevenson, planetary scientist Jonathan Lunine, and chemical engineer Paulette Clancy, published a pioneering study arguing that cell membranes could form under the exotic chemical conditions present on this remarkable moon.

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SETI Talks: The Seas of Titan

Sionascaig Lacus and Urmia Lacus: Temperate Lakes Found on Titan?

Possible temperate lakes on Titan

Authors:

Vixie et al

Abstract:

We analyze southern mid-latitude albedo-dark features on Titan observed by Cassini’s Visual and Infrared Mapping Spectrometer (VIMS). In exploring the nature of these features we consider their morphology, albedo, and specular reflectivity. We suggest that they represent candidates for potential temperate lakes. The presence of lakes at the mid-latitudes would indicate that surface liquid can accumulate and remain stable away from Titan’s poles. Candidate lakes were identified by looking for possible shorelines with lacustrine morphology. Then, we applied an atmospheric correction that empirically solved for their surface albedo. Finally, we looked for a specular reflection of the sky in the identified candidates. Using this prescription, we find two candidates that remain as potential temperature lakes. If candidate features do represent temperate lakes on Titan, they have implications for formation mechanisms such as clouds and rainfall or, in low elevation areas, percolation and subsurface flow. Clouds were observed near candidate lake locations on the T66 flyby and this latitude band showed many clouds during southern summer. Our techniques can be applied to areas of Titan that lack RADAR coverage to search for mid- and low-latitude lakes in the future.

What Nitrogen Compounds may be Dissolved and Precipitated From Titan's Hydrocarbon Seas

Solvation of nitrogen compounds in Titan’s seas, precipitates, and atmosphere

Authors:

Sevenson et al

Abstract:

Saturn’s moon Titan, dominated by its low, 90–95 K, surface temperature and methane seas, is shaped by physical and chemical processes unparalleled in any environment on Earth. Titan’s upper atmosphere produces a rain of compounds such as acetonitrile, acrylonitrile, and acetylene, more familiar to chemical processing plants than to nature. The interaction of these compounds with Titan’s seas is, to a large extent, unknown. As an important first step towards understanding these interactions, we investigate the solvation properties of many of these compounds in methane using multiple theoretical approaches, including cubic equations of state, Statistical Associating Fluid Theory, the Conductor like Screening Model for Real Solvents, and all-atom Molecular Dynamics.

Titan's "Hydrology" is Exotic and Different From Earth's

Titan’s liquids: Exotic behavior and its implications on global fluid circulation

Authors:

Tan et al

Abstract:

Based on a validated model for cryogenic chemical systems, referred to as CRYOCHEM (“Cryogenic Chemistry Model”), surface liquids on Titan are shown to exhibit exotic behavior of density increase with temperature but decrease with pressure, unless the temperature falls below 89.8 K. It is also the case for the atmospheric liquid condensates below an altitude where the liquid density is minimum. The exotic behavior is of compositional origin, which does not have an analog in the atmosphere and liquid water on Earth. As the latitudinal and seasonal variations of surface temperature are known, it is possible to map out the global liquid and vapor density variations as well as the equilibrium phase compositions, which will be useful as inputs for atmospheric general circulation models (GCMs) and investigations of Titan’s methane-equivalent of Earth’s hydrological cycle, local subsurface alkanology (equivalent to hydrology on Earth), lake convection, and clastic and chemical sedimentation in the lakes. Further, the density variations can be used to derive a general idea about global fluid circulation in the upper crust based on averaged conditions on Titan. The surface liquid should tend to flow toward the hottest spot on Titan and a return flow occurs beneath the surface, thus providing analogies with thermohaline circulation in Earth’s oceans. The vapor phase, on the other hand, has ordinary properties that make the global atmospheric circulation similar to the Hadley cell on Earth, but Titan’s cycle reaches the polar regions. The calculated compositions of surface liquids are more methane-rich than other models indicated, thus qualitatively in the right direction to satisfy polar-lake compositions deduced from loss tangents. However, quantitatively there remains a need to find yet more accurate liquid compositions and an optimum equilibrium within constraints of the atmospheric measurements.

Simulating the Tides and Currents of Titan's Kraken Mare

Numerical simulation of tides and oceanic angular momentum of Titan’s hydrocarbon seas

Authors:

Tokano et al

Abstract:

Tides and tidal currents in Titan’s hydrocarbon seas are numerically simulated by a 3-dimensional ocean circulation model using a bathymetry map constrained by Cassini. These predictions are used to calculate the tidally induced variations of the oceanic angular momentum of the seas. The tides behave as a quasi-standing wave with anti-nodes at the northern and southern shores. The tidal currents in Kraken Mare are mainly oriented along the major axis of the sea and are dominated by fast hydraulic currents through a narrow strait. The axial oceanic angular momentum primarily changes due to redistribution of liquids in Kraken Mare and maximizes when there is ebb at the northern shore and flood at the southern shore. On the other hand, variations of the equatorial oceanic angular momentum are contributed by both tides and tidal currents. The oceanic torque between sea and sea bottom is minor compared to its atmospheric counterpart, i.e. the mountain torque between atmosphere and mountains.