Veins of Minerals in Gale Crater on Mars Probably From Evaporating Lakes

Mineral veins found in Mars's Gale Crater were formed by the evaporation of ancient Martian lakes, a new study has shown.

The research, by Mars Science Laboratory Participating Scientists at The Open University and the University of Leicester, used the Mars Curiosity rover to explore Yellowknife Bay in Gale Crater on Mars, examining the mineralogy of veins that were paths for groundwater in mudstones.

The study suggests that the veins formed as the sediments from the ancient lake were buried, heated to about 50 degrees Celsius and corroded.

Professor John Bridges from the University of Leicester Department of Physics and Astronomy said: "The taste of this Martian groundwater would be rather unpleasant, with about 20 times the content of sulphate and sodium than bottled mineral water for instance!

"However as Dr Schwenzer from The Open University concludes, some microbes on Earth do like sulphur and iron rich fluids, because they can use those two elements to gain energy. Therefore, for the question of habitability at Gale Crater the taste of the water is very exciting news."

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A Pop Sci Take on Titan's "Bathtub Scum" (evaporites)

It's not everyday that you get to discover something new. But when you do it is a rather strange and quite brilliant feeling. You don't really cry out 'Eureka' (there's usually about a million things going about it your head pointing out how it could be wrong). When you finally conquer the 'wrong' demon and satisfy yourself that you have something new, well then you usually sit back in your chair and smile to yourself. Maybe at a push grab a cup of coffee and a celebratory chocolate bar from the vending machine. That's pretty much how I felt when I worked out the latest crystal structure I've just published, of the 'bath scum' of Titan.

The great thing about this column space is that I can use it to tell you all the back-story behind a paper, how it came about and why I think it's really exciting.

Titan, the largest moon of Saturn, is in many ways pretty similar to Earth. It's the only moon in the solar system with a substantial atmosphere, much thicker than our own. If you don't mind the cold and lack of oxygen, moving about the surface there will feel a bit like walking under water. It's pretty nice when you consider that the atmosphere most other planets and moons will barely shield you from the vacuum of space.

The other similarity with our own home is that Titan has liquid on the surface, vast lakes and seas. It's the only other place we know where you can watch the sun set into a sea (albeit very very slowly). But, where our seas are composed of water, the seas and lakes of Titan are filled with methane and ethane, which are liquid at the frigid temperatures on the surface (around -180°C). And in fact, the Cassini spacecraft and the team of scientists behind it, have gone further than just the discovery of standing liquid - they have shown that Titan has a kind of hydrological cycle.

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Structure 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, D., Barnes, J.W., Ferreira, A.G. [2013b]. Icarus 226(2),1431–1437), 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.

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.

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.

Evaporite Remnants of Lagoons Found on Mars?

Orbital detection and implications of akaganéite on Mars

Authors:

Carter et al

Abstract:

The martian surface bears the mineralogical record of ancient sub-surface and surface aqueous alteration environments. While most of the chemical alteration produced phyllosilicates, hydrated sulfates and chlorides, other less common compounds provide key constraints on localized geochemical settings, and help refine the geological evolution of the planet. Using orbital imaging spectroscopy data, we report the detection of the iron chlorine hydroxide akaganéite (β-FeOOH, Cl) at several locations of Mars. Akaganéite is known to form in highly saline and chlorinated aqueous environments, and its occurrence in at least three basins of Mars suggests the existence of near-marine (lagoon-like) evaporitic settings early in Mars’ history. As a frequently biogenic mineral, the in-depth study of akaganéite and its relationship with other minerals will also provide an additional benchmark for the assessment of pre-biotic to biotic activity on Mars.

(ps I love that John Carter is the one who is the lead author on this!)

Simulating Titan’s Aerosols

Simulating Titan’s Aerosols in a Three Dimensional General Circulation Model

Authors:

Larson et al

Abstract:

We present results from a new three dimensional GCM with a complete microphysics treatment of the aerosols. We used the Titan Community Atmospheres Model (CAM), to which we have coupled the Community Aerosol and Radiation Model for Atmospheres (CARMA). This model was unable to reproduce superrotating winds without an ad hoc forcing of the zonal winds. Our model was validated by comparing the extinction, optical depth, phase functions, and number densities with data from Cassini and Huygens, as well as other space based and ground based observations. These comparisons allowed us to constrain the microphysical properties of Titan’s haze in the tropics at the time of the Huygens descent. Our best fit of the free aerosol parameters include a haze production rate of 1 x 10-14 g cm-2 s-1 and a charge to radius ratio on the particles of 7.5 e-/μm. Despite recent evidence of equatorial precipitation on Titan, we find the aerosols are only slowly removed by rainfall, less than once in 50 Earth years. One way to fit the wavelength dependence of the optical depth is to model the haze as fractal particles with a changing fractal dimension of 2 above 80 km that increases to 2.8 below 30 km. We investigate the spatial and seasonal variability of Titan’s haze in our model. We find that the haze particle size and number density responds to the dynamics and creates a seasonal cycle in Titan’s albedo.

Benzene, Naphthalene, and Biphenyl are Potential Evaporites on Titan

Dissolution of benzene, naphthalene, and biphenyl in a simulated Titan lake

Authors:

Malasaka et al

Abstract:

We constructed a laboratory apparatus capable of measuring the saturation equilibrium concentration (csat) and dissolution rate constants (keff) of organic solutes in ethane at 94 K. We determined a csat of 18.5 ± 1.9 mg L−1, 0.159 ± 0.003 mg L−1, and 0.039 ± 0.006 mg L−1 for benzene, naphthalene, and biphenyl, respectively. The derived csat and keff can be used to predict the dissolution behavior of the materials in ethane under Titan conditions. The aromatic materials dissolved relatively quickly in liquid ethane at 94 K, reaching saturation in less than 2 h. The dissolution characteristics of benzene in ethane at 94 K are compared to those of terrestrial karst-forming materials in water at 298 K, and are used to constrain Titan surface processes. We discuss the implications of our measurements on the formation of karst on Titan, the concentration of organics in Titan’s lakes, and the formation of evaporite deposits during lake evaporation.

Titan's Climate History Hinted at by Evaporite Locations

Evidence of Titan's Climate History from Evaporite Distribution

Authors:

MacKenzie et al

Abstract:

Water-ice-poor, 5-μm-bright material on Saturn's moon Titan has previously been geomorphologically identified as evaporitic. Here we present a global distribution of the occurrences of the 5-μm-bright spectral unit, identified with Cassini's Visual Infrared Mapping Spectrometer (VIMS) and examined with RADAR when possible. We explore the possibility that each of these occurrences are evaporite deposits. The 5-μm-bright material covers 1\% of Titan's surface and is not limited to the poles (the only regions with extensive, long-lived surface liquid). We find the greatest areal concentration to be in the equatorial basins Tui Regio and Hotei Regio. Our interpretations, based on the correlation between 5-μm-bright material and lakebeds, imply that there was enough liquid present at some time to create the observed 5-μm-bright material. We address the climate implications surrounding a lack of evaporitic material at the south polar basins: if the south pole basins were filled at some point in the past, then where is the evaporite?