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We present thermophysical, biological, and chemical observations of ice and brine samples from five compositionally diverse hypersaline lakes in British Columbia's interior plateau. Possessing a spectrum of magnesium, sodium, sulfate, carbonate, and chloride salts, these low-temperature high-salinity lakes are analogs for planetary ice-brine environments, including the ice shells of Europa and Enceladus and ice-brine systems on Mars. As such, understanding the thermodynamics and biogeochemistry of these systems can provide insights into the evolution, habitability, and detectability of high-priority astrobiology targets. We show that biomass is typically concentrated in a layer near the base of the ice cover, but that chemical and biological impurities are present throughout the ice. Coupling bioburden, ionic concentration, and seasonal temperature measurements, we demonstrate that impurity entrainment in the ice is directly correlated to ice formation rate and parent fluid composition. We highlight unique phenomena, including brine supercooling, salt hydrate precipitation, and internal brine layers in the ice cover, important processes to be considered for planetary ice-brine environments. These systems can be leveraged to constrain the distribution, longevity, and habitability of low-temperature solar system brines—relevant to interpreting spacecraft data and planning future missions in the lens of both planetary exploration and planetary protection. [ABSTRACT FROM AUTHOR]

Comet nuclei in the outer Solar system are constantly irradiated by cosmic rays at low temperatures. Accumulated high concentrations of radicals can undergo fast recombination with significant heating of cometary surface layers. We present the model of comet activity at large heliocentric distances caused by the recombination of radicals. We found that the considered mechanism can cause activity of comets in distant regions of the Solar system, even at the Oort cloud distances. Outbursts in distant comet reservoirs can be a new source of dust and ice particles contributing to the recently discovered anomalous diffuse light in the cosmic extragalactic background optic light and the unexpectedly high flux of dust particles detected by the New Horizons dust counter at the edge of the Kuiper belt. The orbits of small-radii comets in the Oort cloud are highly influenced by cometary outbursts. This effect may account for the observed decrease in the number of small-radius long-period comets. • Recombination of radicals can drive distant cometary outbursts. • Recombination of radicals can lead to significant chemical changes in a comet matter. • Comets in the Oort cloud could be a new possible distant source of dust particles. • The stability of long-period small-radius comets is highly influenced by outbursts. [ABSTRACT FROM AUTHOR]

In order to determine the effect of impact angle on the impact strength of icy planetesimals, we conducted a range of oblique impact experiments for spherical ice and snow targets simulating icy planetesimals at different thermal evolution stages. The ice targets had no porosity and the snow targets had a porosity of 0.5. A polycarbonate or glass sphere impacted the ice targets at 744–1747 m s−1 and the snow targets at 938–5085 m s−1 over a range of impact angles from grazing to head-on collisions. All experiments were conducted using a two-stage light gas gun and a target chamber set in a cold room of −15 °C at Kobe University, Japan. The impact strength, which is a specific energy, Q , when the largest fragment mass is a half of the original target mass, for the ice and snow targets in a head-on collision was determined to be 12 and 520 J kg−1, respectively, whereas it was found that the impact strength depended on the impact velocity. Thus, the normalized largest fragment mass, m l / M t , could well scale with the velocity dependent Q , that is, Q v i γ (where m l and M t are the masses of largest fragment and target, respectively, and v i is the impact velocity). At high Q , m l / M t increased drastically with the decrease of impact angle when the impact angle was smaller than a critical angle, θ c , and θ c ~ 30° for the ice targets and θ c ~ 45° for the snow targets. At small Q , m l / M t continued to increase as the impact angle became smaller for both types of targets. The m l / M t for oblique impacts had a good correlation with the effective specific energy, Q eff = Q sin 2 θ , where θ is the impact angle, and the effective impact strength was determined to be 16 J kg−1 and 499 J kg−1 for the ice and snow targets, irrespective of the impact angle. Furthermore, the scaling parameter, Π s _ eff , which was proposed by Housen and Holsapple (1990) but includes Q eff instead of Q , multiplied by 1 − ϕ λ , where ϕ is the porosity, showed even better correlation with m l / M t , and all m l / M t data of ice and snow targets could be merged, irrespective of impact velocity and ϕ. Based on our experimental results and a theory on the oblique impact of solar system bodies proposed by Shoemaker (1962) , we could estimate the degree of disruption (m l / M t) at any impact energy and any impact angle for icy planetesimals. Our findings demonstrate that the degree of disruption for icy planetesimals that have experienced sufficient thermal evolution was larger than that for those that did not experience significant thermal evolution. • We conducted impact experiments for ice and snow spheres at various impact angles. • We found that impact strength for head-on collisions depended on impact velocity. • Effective specific energy was useful in describing the effect of the impact angle. • We estimated the degree of disruption at various impact energies and impact angles. [ABSTRACT FROM AUTHOR]

James Webb Space Telescope's NIRSpec infrared imaging spectrometer observed the outer solar system dwarf planets Eris and Makemake in reflected sunlight at wavelengths spanning 1 through 5 μm. Both objects have high albedo surfaces that are rich in methane ice, with a texture that permits long optical path lengths through the ice for solar photons. There is evidence for N 2 ice absorption around 4.2 μm on Eris, though not on Makemake. No CO ice absorption is seen at 4.67 μm on either body. For the first time, absorption bands of two heavy isotopologues of methane are observed at 2.615 μm (13CH 4), 4.33 μm (12CH 3 D), and 4.57 μm (12CH 3 D). These bands enable us to measure D/H ratios of (2.5 ± 0.5) × 10−4 and (2.9 ± 0.6) × 10−4, along with 13C/12C ratios of 0.012 ± 0.002 and 0.010 ± 0.003 in the surface methane ices of Eris and Makemake, respectively. The measured D/H ratios are much lower than that of presumably primordial methane in comet 67P/Churyumov-Gerasimenko, but they are similar to D/H ratios in water in many comets and larger outer solar system objects. This similarity suggests that the hydrogen atoms in methane on Eris and Makemake originated from water, indicative of geochemical processes in past or even ongoing hot environments in their deep interiors. The 13C/12C ratios are consistent with commonly observed solar system values, suggesting no substantial enrichment in 13C as could happen if the methane currently on their surfaces was the residue of a much larger inventory that had mostly been lost to space. Possible explanations include geologically recent outgassing from the interiors as well as processes that cycle the surface methane inventory to keep the uppermost surfaces refreshed. • New JWST NIRSpec infrared spectral observations of Eris and Makemake. • Absorption bands of 13CH4 and CH3D used to measure isotopic ratios in CH4. • Similarity to D/H in water suggests source in interior geochemistry. [ABSTRACT FROM AUTHOR]

Nitrogen, carbon monoxide, and methane are key materials in the far outer Solar System where their high volatility enables them to sublimate, potentially driving activity at very low temperatures. Knowledge of their vapor pressures and latent heats of sublimation at relevant temperatures is needed to model the processes involved. We describe a method for using a quartz crystal microbalance to measure the sublimation flux of these volatile ices in the free molecular flow regime, accounting for the simultaneous sublimation from and condensation onto the quartz crystal to derive vapor pressures and latent heats of sublimation. We find vapor pressures to be somewhat lower than previous estimates in literature, with carbon monoxide being the most discrepant of the three species, almost an order of magnitude lower than had been thought. These results have important implications across a variety of astrophysical and planetary environments. • New vapor pressure measurements for N2, CO, and CH4 ices. • Uses quartz crystal microbalance to measure sublimation. • Accounts for simultaneous deposition from surrounding gas. • CO ice has lower vapor pressure than previously thought. [ABSTRACT FROM AUTHOR]

Various Solar System objects are covered in layers of ice that are dominated by H 2 O, CH 4 , and N 2 and in which complex chemical processes take place. In this work, the influence of composition and irradiation duration on the volatile irradiation products of mixed CH 4 :N 2 , CH 4 :H 2 O, and CH 4 :H 2 O:N 2 ices after electron irradiation are studied. The ices were irradiated for 2 or 4 h with 5 keV electrons, followed by a temperature programmed desorption, where the desorption of the volatile irradiation products was observed. The formation of C 2 H x and C 3 H x is observed in all ices and for both irradiation times. For the ices containing H 2 O, molecules as large as tentatively identified C 4 H x and C 5 H x are observed to co-desorb with water, whereas for CH 4 :N 2 a continuous desorption signal is observed instead of a sharp desorption peak. A decrease in signal intensity from the 2 to the 4 h irradiation is observed for most m/z signals in CH 4 :H 2 O and CH 4 :H 2 O:N 2 ices, whereas the opposite is recorded for CH 4 :N 2 , where in general larger signal for longer irradiation duration is seen. The addition of nitrogen to the CH 4 :H 2 O ice did not lead to clear identification of different molecules, but instead to a decrease of the observed signal for complex molecules, suggesting that the addition of nitrogen to the CH 4 :H 2 O mixture primarily leads to a more effective incorporation of material in an organic residue. The analysis of the residue will be subject of future work to complement the findings in this study. • Water in an irradiated ice changes the desorption behavior of complex molecules. • Addition of nitrogen to ices includes more complex molecules into organic residues. • Both of these points combined could have implications for comets and KBOs. [ABSTRACT FROM AUTHOR]

Distinct compressional folding patterns may be an important aspect in shaping icy body surfaces in the outer Solar System and revealing their folding processes and stress histories. Baret Montes on Sputnik Planitia is possibly one of the most folded structures yet observed on Pluto. This glacier consists of subparallel ridges that display a consistent northwest‐southeast orientation and is comparable to Enceladan transpression fold processes. Here we report on mapping using images from NASA's New Horizons mission and apply ridge analysis to determine the folding characteristics and approximate the deformation duration of the folds. This leads to a discussion of the ridge formation mechanism and the possible influence of Sputnik Planitia's underlying convection. Based on the occurrence of the ridges on a water ice based glacier with a thinner layer of methane‐water ice, we conclude that the deformation rates calculated in this study imply the folding duration to be <5.53 My. Plain Language Summary: The Sputnik Planitia region on Pluto houses several large glaciers that consist of a solid water ice base. Baret Montes is the only observable glacier with large, subparallel ridges. Analyzing images from the New Horizons mission, we find that these ridges are formed by the compressional folding of the upper and weaker layer of methane‐water ice, thus leaving ridges. Measuring the spacing of these ridges gives us an estimated emplacement timeline of the folding. Measurements of these ridges can be valuable in constraining glacial ice structures and geophysics on Pluto. Key Points: A major glacial body with prominent ridges (Baret Montes) on Pluto may have undergone compressional stressesThe glacier consists of a water ice base and an upper layer of methane used in modeling a potential strain rateThe deformation rate implies resurfacing of the glacier within 5.53 My [ABSTRACT FROM AUTHOR]

Landslides are among the most widespread geologic features on Ceres. Using data from Dawn's Framing Camera, landslides were previously classified based upon geomorphologic characteristics into one of three archetypal categories, Type 1(T1), Type 2 (T2), and Type 3 (T3). Due to their geologic context, variation in age, and physical characteristics, most landslides on Ceres are, however, intermediate in their morphology and physical properties between the archetypes of each landslide class. Here we describe the varied morphology of individual intermediate landslides, identify geologic controls that contribute to this variation, and provide first‐order quantification of the physical properties of the continuum of Ceres's surface flows. These intermediate flows appear in varied settings and show a range of characteristics, including those found at contacts between craters, those having multiple trunks or lobes; showing characteristics of both T2 and T3 landslides; material slumping on crater rims; very small, ejecta‐like flows; and those appearing inside of catenae. We suggest that while their morphologies can vary, the distribution and mechanical properties of intermediate landslides do not differ significantly from that of archetypal landslides, confirming a link between landslides and subsurface ice. We also find that most intermediate landslides are similar to Type 2 landslides and formed by shallow failure. Clusters of these features suggest ice enhancement near Juling, Kupalo and Urvara craters. Since the majority of Ceres's landslides fall in the intermediate landslide category, placing their attributes in context contributes to a better understanding of Ceres's shallow subsurface and the nature of ground ice. Plain Language Summary: Previously, three distinct types of landslides on Ceres, Type 1 (T1), Type 2 (T2), and Type 3 (T3), were identified and classified by their shapes and locations, but most landslides on Ceres do not fall cleanly into those categories based on shape alone. We have analyzed these intermediate landslides to further describe the continuum of flows seen on Ceres. Here, we study their intrinsic properties to gain a greater understanding of Ceres's subsurface properties. Overall, the locations, shapes, and properties of these landslides on Ceres appear to be influenced by ice contained within Ceres's surface and subsurface materials and suggest local ice enhancement is present in some regions, such as near Juling, Kupalo, and Urvara craters. Key Points: Landslides on Ceres have a wide range of morphologiesSubsurface ice affects the formation of most landslides on Ceres and influences their morphologyCeres has widespread ground ice with ice enhancements near the poles and within Juling and Kupalo craters [ABSTRACT FROM AUTHOR]

Given current uncertainties in the cratering rates and geological histories of icy objects in the outer solar system, it is worth considering how the ages of icy surfaces could be constrained with measurements from future landed missions. A promising approach would be to determine cosmic-ray exposure ages of surface deposits by measuring the amounts of cosmogenic Lithium, Beryllium and Boron at various depths within a few meters of the surface. Preliminary calculations show that ice that has been exposed to cosmic radiation for one billion years should contain these cosmogenic nuclei at concentrations of a few parts per trillion, so any future experiment that might attempt to perform this sort of measurement will need to meet stringent sensitivity requirements. • Surface ages of icy worlds in the outer solar system are uncertain. • Cosmic-ray exposure ages are a promising method of measuring surface ages. • Such ages require measuring Li, Be or B concentrations at parts-per-trillion level. [ABSTRACT FROM AUTHOR]

Highlights • Deuterium and carbon 13 are detected in the rings and on satellite surfaces in the Saturn system. • New methods are presented for deriving isotopic ratios from reflectance spectra of solids. • The D/H ratio of the water in Saturn's rings and icy satellites except Phoebe is close to terrestrial bulk Earth values. • Phoebe's D/H is the highest value yet measured in the Solar system implying an origin in the cold outer Solar System beyond Saturn. • Phoebe also has a high 13C/12C much greater than terrestrial, consistent with an origin in the cold outer Solar System. Abstract Isotopic ratios have long been used to learn about physical processes acting over a wide range of geological environments, and in constraining the origin and/or evolution of planetary bodies. We report the spectroscopic detection of deuterium in Saturn's rings and satellites, and use these measurements to determine the (D/H) ratios in their near-surface regions. Saturn's moons, Phoebe and Iapetus, show a strong signature of CO 2 and the 13C component of this molecule is detected and quantified. Large averages of spectra obtained by the Cassini Visual and Infrared Mapping Spectrometer, VIMS, were computed for the rings and icy satellites. The observed intensities of the infrared absorptions in H 2 O and CO 2 and their isotopes were calibrated using laboratory data and radiative transfer models to derive the D/H and 13C/12C ratios. We find that the D/H in Saturn's rings and satellites is close to the Vienna Standard Mean Ocean Water (VSMOW) and bulk Earth (4% lower than VSMOW) value except for Phoebe, which is 8.3 times the VSMOW value. This is the highest value for any Solar-System surface yet measured, and suggests that Phoebe formed from material with a different D/H ratio than the other satellites in the Saturn system. Phoebe's 13C/12C ratio is also unusual: 4.7 times greater than terrestrial, and greater than values measured for the interstellar medium and the galactic center. The high 13C abundance in the CO 2 suggests that Phoebe was never warm enough for the large D/H ratio in its surface to have originated by evaporative fractionation of its water ice (e.g., from heating in the inner Solar System before its eventual capture by Saturn). We also report the detection of a probable O-D stretch absorption due to OD in minerals on Phoebe at 3.62 μm. This absorption is not detected on other Saturnian satellites. Stronger signatures of bound water absorptions are found in the dark material of Iapetus and we report a new detection of bound water at 1.9 μm. The position of this absorption matches that seen in spectra of hydrated iron oxides but does not match absorptions seen in spectra of tholins. Despite the strong bound water signature in the Iapetus dark material, no 3.62 μm OD absorption is seen in the spectra, further indicating the high deuterium level on Phoebe is unusual. As such, it is likely that Phoebe originated in a colder part of the outer Solar System, relative to the prevailing temperatures at Saturn's distance from the Sun. [ABSTRACT FROM AUTHOR]

Highlights • We map the Ezinu quadrangle on Ceres, the only inner-solar-system dwarf planet. • The geologic history is dominated by impact cratering and associated processes. • Lobate flows are water–ice–rich melt flows emplaced after ballistic ejecta. • Lobate flows and other features indicate localized water–ice–bearing materials. • This work provides context for future investigations of Occator and its faculae. Abstract Dawn is the first spacecraft to visit and orbit Ceres, the largest object in the asteroid belt and the only dwarf planet in the inner Solar System. The Dawn science team undertook a systematic geologic mapping campaign of Ceres' entire surface. Here we present our contribution to this mapping campaign, a geologic map and geologic history of the Ezinu quadrangle, located in the northern mid latitudes from 21–66° N and 180–270° E. From our map, we reconstruct the geologic history of Ezinu quadrangle, which is dominated by impact cratering. Large impact craters that formed a few hundreds to tens of millions of years ago, such as Datan, Messor, Ninsar and Occator, are surrounded by ejecta and contain the products of mass wasting (hummocky crater floor material and talus material) and crater-wall collapse (terrace material). Two of these large impact craters are the sources of lobate flows, which we interpret as melt flows emplaced after the ballistically deposited ejecta. Morphological evidence suggests these lobate flows are rich in water–ice-bearing material that was excavated during the formation of the impact craters. There are only a few localized occurrences of lobate flows, suggesting that the water–ice-bearing source materials have restricted extents and/or are deeply buried within Ceres' subsurface. The quadrangle also contains a variety of linear features: secondary crater chains are formed by the impact of locally and globally sourced material and pit chains and grooves are formed by the collapse of surficial materials into sub-surface fractures. The Ezinu quadrangle contains the northern portion of Occator crater, which is the host crater of prominent bright regions called faculae. Our geologic analysis therefore also provides context for the future investigation of Occator and its intriguing faculae. [ABSTRACT FROM AUTHOR]

The Earth-Moon and other planetary objects are enriched in the heavier isotopes, 17O and 18O, relative to 16O by several %, compared to the Sun. A stunning exception is the magnetite/sulfide symplectite found in Acfer 094 meteorite, which shows 24% enrichment in 17,18O. Here we show that the SO and SO 2 molecules in the molecular cloud, ∼106% enriched in 17,18O relative to the Sun, evolved through the protoplanetary disk and planetesimal stages to become a sulfuric acid, 24% enriched in 17,18O. The sulfuric acid provided a cryofluid environment in the planetesimal and by itself reacted with ferric iron to form an amorphous ferric-hydroxysulfate-hydrate, which eventually decomposed into the symplectite by shock. We indicate that the Acfer 094 symplectite and its progenitor, sulfuric acid, is strongly coupled with the material evolution in the solar system since the days of our molecular cloud. We interrogate a petrographic relationship of the symplectite to the Acfer 094 meteorite matrix for an additional clue to its origin. In light of the comparative study of Acfer 094 with other "primordial" chondrites that contain amorphous silicate matrices and with GEMS, we conclude that the cryofluid condition was critical to the formation of the Acfer 094 symplectite. • Sulfuric acid is a carrier of 16O-poor, 17,18O-rich isotopes in Acfer 094 meteorite. • Cryofluid alteration in planetesimals caused by sulfuric acid and hydrogen peroxide. • Sulfuric acid in protoplanetary disk originated fromSO and SO2in molecular clouds. • Ferric hydroxysulfate gels, a precursor, converted to cosmic symplectite by shock. • Low-temperature alteration in parent body generates colloidal/amorphous silicates. [ABSTRACT FROM AUTHOR]

The Martian climate throughout the Amazonian is widely believed to have been cold and hyper-arid, very similar to the current conditions. However, ubiquitous evidence of aqueous and glacial activity has been recently reported, including channels that can be tens to hundreds of kilometres long, alluvial and fluvial deposits, ice-rich mantles, and glacial and periglacial landforms. Here we study a ∼340 km-long fluvial system located in the Terra Cimmeria region, in the southern mid-latitudes of Mars. The fluvial system is composed of an upstream catchment system with narrow glaciofluvial valleys and remnants of ice-rich deposits. We observe depositional features including fan-shaped deposits, and erosional features such as scour marks and streamlined islands. At the downstream section of this fluvial system is an outflow channel named Kārūn Valles, which displays a unique braided alluvial fan and terminates on the floor of the Ariadnes Colles basin. Our observations point to surface runoff of ice/snow melt as the water source for this fluvial activity. According to our crater size–frequency distribution analysis the entire fluvial system formed during early to middle Amazonian, between ∼ 1 . 8 − 0.2 + 0.2 Ga to 510 − 40 + 40 Ma. Hydraulic modelling indicates that the Kārūn Valles and consequently the alluvial fan formation took place in geologically short-term event(s). We conclude that liquid water was present in Terra Cimmeria during the early to middle Amazonian, and that Mars during that time may have undergone several episodic glacial-related events. [ABSTRACT FROM AUTHOR]

We find evidence for hydrated material in the lunar regolith using “albedo protons” measured with the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter (LRO). Fluxes of these albedo protons, which are emitted from the regolith due to steady bombardment by high energy radiation (Galactic Cosmic Rays), are observed to peak near the poles, and are inconsistent with the latitude trends of heavy element enrichment (e.g., enhanced Fe abundance). The latitudinal distribution of albedo protons anti-correlates with that of epithermal or high energy neutrons. The high latitude enhancement may be due to the conversion of upward directed secondary neutrons from the lunar regolith into tertiary protons due to neutron–proton collisions in hydrated regolith that is more prevalent near the poles. The CRaTER instrument may thus provide important measurements of volatile distributions within regolith at the Moon and potentially, with similar sensors and observations, at other bodies within the Solar System. [ABSTRACT FROM AUTHOR]

We recently reported on the reddish coloration of a CH 3 OH/H 2 O ice irradiated by cryoplasma, which is similar in appearance to the reddish surfaces seen on some icy bodies in the outer Solar System, and is sustained only at cryogenic temperatures. In this study, we analyzed the time evolution of absorption spectra during irradiation of this ice at temperatures of 70–90 K, and found that the nominal production rates of the reddish materials decreased with increasing temperature. We conducted kinetic analysis, which revealed that although the formation of the materials that absorb at 500 nm showed no temperature dependence, their disappearance under cryoplasma irradiation showed a positive temperature dependence. This finding indicates that the interactions of excited plasma species with the reddish materials, coupled with thermally-driven processes, can increase the rates of disappearance of the reddish materials and result in their destruction even at temperatures below their thermal dissociation temperatures, which was found to be 120–150 K in our previous study. These results suggest that the effects of radiation-driven chemistry and thermally-driven chemistry in concert can influence the formation and stability of reddish materials such as those synthesized in this study. • Reddish materials synthesized on ice show two or more components in UV–visible. • Net production rate of reddish materials decreased at higher irradiation temperature. • Reddish materials destroyed below thermal dissociation temperature by irradiation. [ABSTRACT FROM AUTHOR]

Impact jetting during planetesimal collisions is a process that ejects small amounts of highly shocked material during the earliest stages of an impact. Jetting can produce melted and vaporized material during relatively low velocity collisions and has previously been presented as a mechanism for producing chondrules in the inner solar system during impacts between rocky planetesimals. However, chondrules are observed in both non‑carbonaceous and carbonaceous chondrites, which are thought to have formed in the inner and outer solar system, respectively. In this work, we use the iSALE2D hydrocode to investigate the viability of jetting for producing chondrules in the outer solar system, where ice-rich bodies begin to be incorporated into the planetesimal population. We create mixed material equations of state for ice mass fractions of 10–50% intimately combined with dunite to emulate the compositions of ice-rich outer solar system planetesimals. We account for collisions between a sphere and flat target at 2–7 km/s. Our results indicate that the presence of ice lowers the total mass of chondrule forming material jetting can produce, but a significant mass of chondrules is likely to form nonetheless even through collisions of bodies with relatively high ice concentrations. For example, for collisions at 4 km/s, pure dunite bodies create ~1% the mass of a 10-km-diameter projectile of chondrules, while bodies that include 50% ice by mass produce ~0.004% the mass of an impactor of chondrules. The presence of ice results in water vapor in the jet plume which may generate an oxidizing environment that favors the production of chondrules relatively enriched in 17O and 18O due to 16O-poor composition of water ice in the outer solar system. • Jetting during icy impacts is proposed to form chondrules in the outer Solar System. • Significant chondrule mass may be formed during mixed ice-rock accretionary impacts. • Oxygen isotopic exchange with silicate melt may occur in water vapor-rich jet plume. • Impact jetting may be a chondrule forming mechanism throughout the Solar System. [ABSTRACT FROM AUTHOR]

Iapetus possesses two spectacular characteristics: (i) a high equatorial ridge which is unique in the Solar System and (ii) a large flattening ( a - c = 34 km) inconsistent with its current spin rate. These two main characteristics have probably been acquired in Iapetus’ early past as a consequence of coupled interior-rotation evolution. Previous models have suggested that rapid despinning may result either from enhanced internal dissipation due to short-lived radioactive elements or from interactions with a sub-satellite resulting from a giant impact. For the ridge formation, different exogenic and endogenic hypotheses have also been proposed, but most of the proposed scenarios have not been tested numerically. In order to model simultaneously internal heat transfer, tidal despinning and shape evolution, we have developed a two-dimensional axisymmetric thermal convection code with a deformable surface boundary, coupled with a viscoelastic code for tidal dissipation. The model includes centrifugal and buoyancy forces, a composite non-linear viscous rheology as well as an Andrade rheology for the dissipative part. By considering realistic rheological properties and by exploring various grain size values, we show that, in the absence of additional external interactions, despinning of a fast rotating Iapetus is impossible even for warm initial conditions ( T > 250 K). Alternatively, the impact of a single body with a radius of 250–350 km at a velocity of 2 km/s may be sufficient to slow down the rotation from a period of 6–10 h to more than 30 h. By combining despinning due to internal dissipation and an abrupt change of rotation due to a giant impact, we determined the parameters leading to a complete despinning and we computed the corresponding shape evolution. We show that stresses arising from shape change affect the viscosity structure by enhancing dislocation creep and can lead to the formation of a large-scale ridge at the equator as a result of rapid rotation change for initial rotation periods of 6 h. [ABSTRACT FROM AUTHOR]

Rock and soil surface layers absorb and reflect incoming solar radiation immediately at the surface. Ices on the other hand, whilst opaque in the infrared, are partially transparent in the visible spectral range. These properties are responsible for the “solid-state greenhouse effect” (SSGE), which may play an important role in the energy balance of icy surfaces in the Solar System. To model the SSGE, we need to know not only thermal properties but also optical properties such as the albedo and the absorption scale length of the ice. We have investigated the absorption scale length, also known as e-folding scale, of snow/dust mixtures within the scope of a project directed at investigating the behaviour of the martian polar caps. After measuring the e-folding scale of recrystallized snow we can now also relate the dust content of contaminated snow to the penetration depth of sunlight into the mixture. Equally important, however, is our observation that light penetration through the mixture is dramatically affected by small-scale inhomogeneities. [ABSTRACT FROM AUTHOR]

Positive, superisostatic gravity anomalies (also known as mass concentrations or "mascons") are found beneath some large impact basins on Ceres, including Kerwan and Yalode. Such anomalies may be due to high-density mantle material that has been uplifted towards the surface, a process comparable to that on rocky bodies. Alternatively, the anomalies may be caused by impact energy devolatilizing the icy crust beneath the impact site, leaving a denser, ice-poor portion of material below the surface. The two hypotheses would result in different simple-to-complex transition diameters of craters superposing the larger basins. We analyzed crater morphology in order to deduce transition diameters of superposed craters in the Kerwan and Yalode basins. The surveyed locations produced transition diameters between 7 and 14 km. This transition diameter is consistent with that of average cerean crust composed of a mixture of both rock and ice, and not of a purely rocky crust which would produce a transition diameter of about 30 km. Our results have two possible interpretations. First, positive gravity anomalies beneath the basins are due to mantle uplift, rather than devolatilization of local crust. Second, impact-induced devolatilization is an incomplete process, removing enough ice to substantially increase crustal density but leaving enough ice to cause later impact processes to be ice-controlled. We favor the former explanation as the simpler interpretation, which would imply that mascons formed by impact-induced mantle uplift is a common process in the Solar System, and not just confined to rocky planets. • Crustal ice content in large basins can be constrained with superposed craters. • Morphology of craters superposing mascons is consistent with ice-rich local crust. • Mascons on Ceres are at least partly the result of mantle uplift. [ABSTRACT FROM AUTHOR]

Comets are expected to be the most primitive objects in the Solar System. The chemical composition of these objects is frequently assumed to be directly provided by the observations of the abundances of volatile molecules in the coma. The present work aims to determine the relationship between the chemical composition of the coma, the outgassing profile of volatile molecules and the internal chemical composition, and water ice structure of the nucleus, and physical assumptions on comets. To do this, we have developed a quasi 3D model of a cometary nucleus which takes into account all phase changes and water ice structures (amorphous, crystalline, clathrate, and a mixture of them); we have applied this model to the Comet 67P/Churyumov-Gerasimenko, the target of the Rosetta mission. We find that the outgassing profile of volatile molecules is a strong indicator of the physical and thermal properties (water ice structure, thermal inertia, abundances, distribution, physical differentiation) of the solid nucleus. Day/night variations of the rate of production of species helps to distinguish the clathrate structure from other water ice structures in nuclei, implying different thermodynamic conditions of cometary ice formation in the protoplanetary disc. The relative abundance (to H 2 O) of volatile molecules released from the nucleus interior varies by some orders of magnitude as a function of the distance to the Sun, the volatility of species, their abundance and distribution between the ”trapped” and ”condensed” states, the structure of water ice, and the thermal inertia and other physical assumptions (dust mantle, …) on the nucleus. For the less volatile molecules such as CO 2 and H 2 S, the relative (to H 2 O) abundance of species in coma remain similar to the primitive composition of the nucleus (relative deviation less than 25%) only around the perihelion passage (in the range −3 to −2 to +2–3 AU), whatever is the water ice structure and chemical composition, and under the conditions that the nucleus is not fully covered by a dust mantle. The relative (to H 2 O) abundance of highly volatile molecules such as CO and CH 4 in the coma remain approximately equal to the primitive nucleus composition only for nuclei made of clathrates. The nucleus releases systematically lower relative abundances of highly volatile species (up to one order of magnitude) around perihelion (in the range −3 to −2 to +2–3 AU) in the cases of the crystalline and amorphous water ice structures in the nuclei. The rate of production, the outgassing profile and the relative abundances (to H 2 O) of volatile molecules are the key parameters allowing one to retrieve the chemical composition and thermodynamic conditions of cometary ice formation in the early Solar System. The coming observations of the coma and nucleus by the Rosetta mission instruments (VIRTIS, MIRO, …) should provide the necessary constraints to the model to allow it to infer the primordial ice structure and composition of the comet. [ABSTRACT FROM AUTHOR]

Scattering by particles significantly smaller than the wavelength is an important physical process in the icy and rocky bodies in our Solar System and beyond. A number of observations of spectral bluing (referred to in those papers as 'Rayleigh scattering') on planetary surfaces and cometary comas have been recently reported, however, the necessary mathematical modeling of this phenomenon has not yet achieved maturity. This paper is a first step to this effect, by examining the effect of grain size and optical index on the albedo of small conservative and absorbing particles as a function of wavelength. The conditions necessary for maximization of spectral bluing effects in real-world situations are identified. We find that any sufficiently narrow size distribution of scattering particles will cause spectral bluing in some part of the EM spectrum regardless of its optical index. We also investigate the effect of including a distribution of particle sizes. [ABSTRACT FROM AUTHOR]

The lunar polar regions contain permanently shadowed regions (PSRs) or local topographic depressions that never receive direct sunlight. These environments (<110 K) have the potential to cold-trap volatile materials in the form of ice, which are essential resources for exploration and industrialization of cislunar space and the Solar System. Orbital observations and those from the LCROSS impactor experiment provide evidence of the existence of water ice and other cold-trapped volatiles in PSRs; however, constraints on volatile abundance and distribution remain ambiguous as individual observations are not always in concord. Here we compile observations indicating the presence of volatiles from ten remotely sensed datasets in 65 PSRs to estimate the locations and mass of water ice deposits. Faustini, Cabeus, de Gerlache, Shoemaker, Haworth, Sverdrup, Slater, and Amundsen are likely the most resource-rich PSRs. Based on co-locations of observations indicative of surface frost and subsurface hydrogen abundance, we find that the craters with the highest potential mass in metric tons (t) of water ice include Cabeus (~11 × 106 t), Shoemaker (~5 × 106 t), Faustini (~4 × 106 t), de Gerlache (~3 × 106 t), and Haworth (~3 × 106 t). Future prospecting of lunar volatiles and water ice is contingent on filling knowledge gaps in resource potential, notably accurate measurements of grade and depth of volatiles. Our proposed ranking and estimates for resource tonnage are a tool to guide future orbital and landed missions that could accurately determine the resource potential of PSR deposits. • Identified eight PSRs with the highest resource potential • Faustini PSR shows the strongest indication of water ice based on our criteria • We estimate that Haworth crater has the greatest tonnage of surface frost • Cabeus crater has the greatest estimated tonnage of subsurface hydrogen deposits • We estimate subsurface ice deposits are more spatially extensive than frost [ABSTRACT FROM AUTHOR]

Highlights: [•] Comet C/2009 P1 Garradd was observed in 117 SOHO/SWAN H-Lyα images over 8months. [•] Calculated water production rates monitor the activity over the entire apparition. [•] The activity peaked and was generally much higher before perihelion than after. [•] After perihelion the activity varied as sublimation from a constant water surface area. [•] Substantial pre-perihelion production of H2O from icy grains may be indicated. [ABSTRACT FROM AUTHOR]

Abstract: The icy worlds of the outer Solar System are of significant astrobiological interests due, in large part, to the evidence of liquid water beneath the surfaces of a number of jovian and saturnian satellites. Many of these surfaces are subject to various levels of particle and photon radiation. If molecular compounds of biological origin are present in the surface ice layer (originating either in situ or delivered from a subsurface aqueous environment), can they be detected as evidence of biological activity, or do they decompose too rapidly in the surface radiation environment? We present a wavelength resolved study of the ultraviolet photolysis of glycine and phenylalanine to address this question. Studying these reactions at multiple discreet wavelengths distinguishes the present work from previous matrix isolation studies using hydrogen flow lamps and continuum sources by resolving the important contribution of photons with energies much lower than Lyman-α (121.6nm). We find that although the half-lives of glycine and phenylalanine are essentially identical at 147nm, they diverge at 206nm and diverge significantly at 254nm with glycine having longer half-lives at these longer wavelengths. Scaling the results to account for the wavelength dependent variation in solar irradiance shows that despite the reduction of photon energies in the 200–250nm range, versus 147nm, it is the longer wavelengths that will dominate the destruction of amino acids in icy surfaces. It seems unlikely that organics can survive long enough on the surface of an icy planetary body to be detected without being frequently replenished from a shielded source such as a subsurface ocean. [Copyright &y& Elsevier]

Abstract: In this work, we present a new model for the heat conductivity of porous dust layers in vacuum, based on an existing solution of the heat transfer equation of single spheres in contact. This model is capable of distinguishing between two different types of dust layers: dust layers composed of single particles (simple model) and dust layers consisting of individual aggregates (complex model). Additionally, we describe laboratory experiments, which were used to measure the heat conductivity of porous dust layers, in order to test the model. We found that the model predictions are in an excellent agreement with the experimental results, if we include radiative heat transport in the model. This implies that radiation plays an important role for the heat transport in porous materials. Furthermore, the influence of this new model on the Hertz factor are demonstrated and the implications of this new model on the modeling of cometary activity are discussed. Finally, the limitations of this new model are critically reviewed. [Copyright &y& Elsevier]

Abstract: Knowing the collisional process among small porous icy bodies in the outer solar system is a key to understanding the formation of EKBOs and the evolution of icy planetesimals. Impact experiments of sintered porous ice spheres with 40%, 50%, 60% and 70% porosity were conducted by using three types of projectiles at the impact velocity from 2.4 to 489m/s, and we studied the effects of porosity on the collisional processes. Projectile sticking occurred at the impact velocity higher than 44m/s for 60% porosity targets and higher than 13m/s for 70% porosity targets. The antipodal velocity of the porous ice target increased with the increase of energy density, Q, and it increased slightly with the increase of porosity, although it was exceptionally high in cases when the projectile penetrated the target. The shattering strength of porous ice targets was found to decrease from 100 to 31J/kg with the increase of porosity from 40% to 70%. The cumulative fragment mass distribution was found to depend on the energy density and the target porosity, and the slopes of the distribution in the small fragment region were almost flat for more porous targets. We reanalyzed the cumulative fragment mass distribution and first obtained the empirical equation showing the fragment mass distribution of porous ice targets as a function of the energy density and the porosity. [Copyright &y& Elsevier]

Abstract: Shock-induced melting and vaporization of H2O ice during planetary impact events are widespread phenomena. Here, we investigate the mass of shock-produced liquid water remaining within impact craters for the wide range of impact conditions and target properties encountered in the Solar System. Using the CTH shock physics code and the new 5-phase model equation of state for H2O, we calculate the shock pressure field generated by an impact and fit scaling laws for melting and vaporization as a function of projectile mass, impact velocity, impact angle, initial temperature, and porosity. Melt production nearly scales with impact energy, and natural variations in impact parameters result in only a factor of two change in the predicted mass of melt. A fit to the π-scaling law for the transient cavity and transient-to-final crater diameter scaling are determined from recent simulations of the entire cratering process in ice. Combining melt production with π-scaling and the modified Maxwell Z-model for excavation, less than half of the melt is ejected during formation of the transient crater. For impact energies less than about 2×1020 J and impact velocities less than about 5kms−1, the remaining melt lines the final crater floor. However, for larger impact energies and higher impact velocities, the phenomenon of discontinuous excavation in H2O ice concentrates the impact melt into a small plug in the center of the crater floor. [Copyright &y& Elsevier]

Abstract: Using the light gas gun at the Open University’s Hypervelocity Impact facility, a series of impact experiments exploring impacts into water ice and gypsum have been performed. Fragmentation of solid ejecta was recorded using two different methods, analysed and compared with the total ejecta. Preliminary results show that the size distribution of the ejecta fragments from water ice is very similar to those from gypsum. These results also represent a step towards a better understanding of ejecta fragmentation in geological materials, including icy surfaces in the Solar System. [Copyright &y& Elsevier]

Abstract: Our knowledge about the physical processes determining the activity of comets were mainly influenced by several extremely successful space missions (Giotto, Deep Space I, Stardust, Deep Impact and EPOXI), the predictions of theoretical models and the results of laboratory experiments. However, novel computer models should not be treated in isolation but should be based on experimental results and should be verified and calibrated by experimental work. Therefore, a new experimental setup was constructed to investigate the temperature dependent sublimation properties of hexagonal water ice and the gas diffusion through a dry dust layer covering the ice surface. We show that this experimental setup is capable to reproduce known gas production rates of pure hexagonal water ice. The reduction of the gas production rate due to an additional dust layer on top of the ice surface was measured and compared to the results of another experimental setup in which the gas diffusion through dust layers at room temperature was investigated. We found that the relative permeability of the dust layer is inversely proportional to its thickness, which is also predicted by theoretical models. However, the measured absolute weakening of the gas flow was smaller than predicted by models. This lack of correspondence between model and experiment may be caused by an ill-determination of the boundary condition in the theoretical models, which further demonstrates the necessity of laboratory investigations. Furthermore, the impedance of the dust layer to the ice evaporation was found to be similar to the impedance at room temperature, which means that the temperature profile of the dust layer is not influencing the reduction of the gas production. Finally, we present the results of an extended investigation of the sublimation coefficient, which is an important factor for the description of the sublimation rate of water ice and, thus, an important value for thermophysical modeling of icy bodies in the Solar System. The achieved results of this laboratory investigations demonstrate that experimental works are essential for the understanding of the origin of cometary activity. [Copyright &y& Elsevier]

Abstract: The Cassini mission revealed two spectacular characteristics of Iapetus: (1) a geologically old and high equatorial ridge, which is unique in the Solar System and (2) a large flattening of 35km consistent with the equilibrium figure for a hydrostatic body rotating with a period of 16h, whereas the current spin period is 79.33 days. This study describes three-dimensional simulations of solid-state convection within an undifferentiated Iapetus. It investigates the implications for the evolution of the interior thermal structure and its spin rate and global shape using radially layered viscoelastic models. The role of the concentration in the short-lived radiogenic element [26Al], just after accretion is completed, is specifically addressed. The first result is to show that whatever the [26Al] value, convection occurs. As suggested by Castillo-Rogez et al. [Castillo-Rogez, J., Matson, D., Sotin, C., Johnson, T., Lunine, J., Thomas, P. [2007] Icarus, 190, 179–202], convection reduces the warming of the interior compared to the conductive evolution and therefore limits the conditions for despinning. In our calculations, two conceptual linear viscoelastic models are used. When considering a Maxwell rheology, the interior temperature (viscosity) never reaches a value high (low) enough to induce despinning. In order to promote dissipation at low temperature, a Burgers rheology, which includes an additional dissipation peak, is introduced. For favorable parameter values, this latter rheology leads to despinning. However, only models associated with large amounts of short-lived radiogenic elements lead to the observed flattening. This suggests that the accretion process needs to be completed shortly after the formation of CAIs (Calcium–Aluminum-rich Inclusions) (⩽4Myr). For [26Al] varying between 72 and 46ppb, the observed flattening is obtained only for a limited range of initial spin period, between 9.5 and 10.2h. For [26Al] ranging between 30 and 15ppb, initial spin rates smaller than 8.5h are required. For smaller values of [26Al], the body is too cold and viscous to acquire a significant flattening even if a rotation period close to the body disruption limit is considered. Even with a thin lithosphere during the early stage, our simulations show that Iapetus never reaches the equilibrium figure for a hydrostatic body due to the non-zero rigidity of the lithosphere. The 35km value of the flattening is the result of the partial relaxation of an ancient larger flattening ranging between 45 and 80km, depending on the evolution of the lithosphere thickness mainly controlled by the radiogenic content. A thin lithosphere is consistent with an early building of the equatorial ridge. The lithosphere thickening due to interior cooling can explain the preservation of the ridge throughout the remaining evolution of Iapetus. [Copyright &y& Elsevier]

Abstract: Optical constants in a broad temperature and wavelength range are important input parameters in radiative transfer models used in studies of planetary atmospheres. In the laboratory, the refractive index values of ices at the HeNe laser wavelength (632.8nm) are often used to monitor the growth rate and thickness of ice films. In this report we present laboratory measurements determining the refractive index at 632.8nm of ammonia and hydrocarbon ices in the temperature range 80–100K. Thin ice films are vapor-deposited on a cryogenically cooled mirror located inside a high-vacuum apparatus. The real component of the refractive index of these ice films is determined by a two-angle interferometric technique. Optical modeling calculations of the transmittance and reflectance through the thin ice films assist in the interpretation of the experimental results. We discuss our results and compare them with other measurements available in the literature. The results reported here are relevant to the spectroscopy of icy objects in the solar system; they are needed to perform laboratory characterization of ices, derive optical constants, and model spectra. [Copyright &y& Elsevier]

Abstract: Saturn’s satellite Dione is becoming an increasingly important object in the outer Solar System, as evidence for its current activity accumulates. Infrared observations of the surface can provide clues to the history of the body and currently active processes. Using data from the Cassini Visual and Infrared Mapping Spectrometer (VIMS), we perform three sets of analyses that are sensitive to the ice state, temperature, thermal history, grain size and composition of surface ice. These are calculation of a “crystallinity factor”, spectral ratios and water ice band depths. In our analysis, we focus on the dichotomy between the wispy and dark terrain on Dione’s trailing hemisphere, to better understand the source of the different materials and their current properties. Our results suggest two different scenarios: (1) the ice from the wispy region has a higher crystallinity and water ice content than the dark region or (2) the wispy region contains larger grains. Both of these models imply recent geologic activity on Dione. [Copyright &y& Elsevier]

Abstract: We present experimental results in order to understand the physico-chemical effects induced by fast ions irradiating sulfur bearing molecules. The experiments are relevant both to Solar System objects (icy satellites, comets, TNOs) and icy mantles on grains in the interstellar medium. Here we concentrate on the application to the Galilean moons that are exposed to high energetic particle fluxes in the jovian magnetosphere. In particular we show that: [–] Implantation of sulfur ions into water ice produces hydrated sulfuric acid with high efficiency providing an important contribution to the sulfur cycle on the surfaces of Europa and other jovian satellites. [–] Implantation of protons into sulfur dioxide produces mainly SO3, polymers, and O3 but not H–S bonds. The suggested hypothesis that H implantation could result in the formation of H2SO3 on Io is not confirmed by our experiments. [–] Irradiation of sulfur dioxide mainly produces SO3 and sulfur polymers. [–] Irradiation and subsequent warming of H2S induces the formation of a sulfurous residue that exhibits S–H bonds. [–] Water ice has been deposited on refractory sulfurous materials originating from SO2 or H2S irradiation. We looked to the formation of new species at the interface (ion mixing). We have not found evidence for the efficient synthesis of SO2. In the case of residues rich in species containing S–H bonds, H2S is re-formed. [Copyright &y& Elsevier]

Abstract: To date, there is no core accretion simulation that can successfully account for the formation of Uranus or Neptune within the observed 2–3 Myr lifetimes of protoplanetary disks. Since solid accretion rate is directly proportional to the available planetesimal surface density, one way to speed up planet formation is to take a full accounting of all the planetesimal-forming solids present in the solar nebula. By combining a viscously evolving protostellar disk with a kinetic model of ice formation, which includes not just water but methane, ammonia, CO and 54 minor ices, we calculate the solid surface density of a possible giant planet-forming solar nebula as a function of heliocentric distance and time. Our results can be used to provide the starting planetesimal surface density and evolving solar nebula conditions for core accretion simulations, or to predict the composition of planetesimals as a function of radius. We find three effects that favor giant planet formation by the core accretion mechanism: (1) a decretion flow that brings mass from the inner solar nebula to the giant planet-forming region, (2) the fact that the ammonia and water ice lines should coincide, according to recent lab results from Collings et al. [Collings, M.P., Anderson, M.A., Chen, R., Dever, J.W., Viti, S., Williams, D.A., McCoustra, M.R.S., 2004. Mon. Not. R. Astron. Soc. 354, 1133–1140], and (3) the presence of a substantial amount of methane ice in the trans-saturnian region. Our results show higher solid surface densities than assumed in the core accretion models of Pollack et al. [Pollack, J.B., Hubickyj, O., Bodenheimer, P., Lissauer, J.J., Podolak, M., Greenzweig, Y., 1996. Icarus 124, 62–85] by a factor of 3–4 throughout the trans-saturnian region. We also discuss the location of ice lines and their movement through the solar nebula, and provide new constraints on the possible initial disk configurations from gravitational stability arguments. [Copyright &y& Elsevier]

Abstract: We report a study on the broadband ultraviolet photolysis of methane–water ice mixtures, at low methane concentrations and temperatures relevant to the icy satellites of the outer Solar System. The photochemistry of these mixtures is dominated by the action of hydroxyl radicals on methane and the resulting products. This implies that, given sufficient exposure time, the methane will eventually be completely oxidized to carbon dioxide. The presence of methane inhibits the formation of hydrogen peroxide by serving as a trap for hydroxyl radicals. The distribution of photochemical products is broadly similar to that previously conducted using ion and electron sources, with some differences possibly attributable to the difference in radiation source. The results are applicable to a variety of icy bodies in the Solar System. On Enceladus, where methane mixed with water is measured in the plumes, methane in the surface ices is subject to oxidation and will eventually be converted to CO2. The C feature detected in the VIMS spectra of the Enceladus surface ice suggests that methane is currently being supplied to the surface ice, likely from re-condensation of the plume gas. [Copyright &y& Elsevier]

Ground-based telescopes and space exploration have provided outstanding observations of the complexity of icy planetary surfaces. This work presents our review of the varying nature of carbon dioxide (CO2) and carbon monoxide (CO) ices from the cold traps on the Moon to Pluto in the Kuiper Belt. This review is organized into five parts. First, we review the mineral physics (e.g., rheology) relevant to these environments. Next, we review the radiation-induced chemical processes and the current interpretation of spectral signatures. The third section discusses the nature and distribution of CO2 in the giant planetary systems of Jupiter and Saturn, which are much better understood than the satellites of Uranus and Neptune, discussed in the subsequent section. The final sections focus on Pluto in comparison to Triton, having mainly CO, and a brief overview of cometary materials. We find that CO2 ices exist on many of these icy bodies by way of magnetospheric influence, while intermixing into solid ices with CH4 (methane) and N2 (nitrogen) out to Triton and Pluto. Such radiative mechanisms or intermixing can provide a wide diversity of icy surfaces, though we conclude where further experimental research of these ices is still needed. [ABSTRACT FROM AUTHOR]

Abstract: Earth, Jupiter''s moon Io and Saturn''s tiny moon Enceladus are the only solid objects in the Solar System to be sufficiently geologically active for their internal heat to be detected by remote sensing. Interestingly, the endogenic activity on Enceladus is only located on a specific region at the south pole, from which jets of water vapor and ice particles have been observed [Spencer, J.R., and 9 colleagues, 2006. Science 311, 1401–1405; Porco, C.C., and 24 colleagues, 2006. Science 311, 1393–1401]. The current polar location of the thermal anomaly can possibly be explained by diapir-induced reorientation of the satellite [Nimmo, F., Pappalardo, R.T., 2006. Nature 441, 614–616], but the thermal anomaly triggering and the heat power required to sustain it over geological timescales remain problematic. Using a three-dimensional viscoelastic numerical model simulating the response of Enceladus to tidal forcing, we explore the effect of a low-viscosity anomaly in the ice shell, localized to the south polar region, on the tidal dissipation patterns. We demonstrate that only interior models with a liquid water layer at depth can explain the observed magnitude of dissipation rate and its particular location at the south pole. Moreover, we show that tidally-induced heat must be generated over a relatively broad region in the southern hemisphere, and it is then transferred toward the south pole where it is episodically released during relatively short resurfacing events. As large tidal dissipation and internal melting cannot be induced in the south polar region in the absence of a pre-existing liquid decoupling layer, we propose that liquid water must have been present in the interior for a very long period of time, and possibly since the satellite formation. Owing to the orbital equilibrium requirement [Meyer, J., Wisdom, J., 2007. Icarus 188, 535–539], sustaining some liquid water at depth is impossible if heat is continuously emitted at a rate of 4–8 GW at the south pole. Based on that requirement, we propose that the current thermal emission is not in equilibrium with the heat production, and that the thermal emission rate is abnormally high at present time. Alternatively, continuous dissipation at a rate of 1–2 GW in the ice shell at the south pole should be sufficient to induce internal melting and it could sustain a layer of liquid water at depth over geologic timescales. [Copyright &y& Elsevier]

Abstract: Ices in the solar system are observed on the surface of planets, satellites, comets and asteroids where they are continuously subordinate at particle fluxes (cosmic ions, solar wind and charged particles caught in the magnetosphere of the planets) that deeply modify their physical and structural properties. Each incoming ion destroys molecular bonds producing fragments that, by recombination, form new molecules also different from the original ones. Moreover, if the incoming ion is reactive (H+, O n+, S n+, etc.), it can concur to the formation of new molecules. Those effects can be studied by laboratory experiments where, with some limitation, it is possible to reproduce the astrophysical environments of planetary ices. In this work, we describe some experiments of 15–100keV H+ and He+ implantation in pure sulfur dioxide (SO2) at 16 and 80K and carbon dioxide (CO2) at 16K ices aimed to search for the formation of new molecules. Among other results we confirm that carbonic acid (H2CO3) is formed after H-implantation in CO2, vice versa H-implantation in SO2 at both temperatures does not produce measurable quantity of sulfurous acid (H2SO3). The results are discussed in the light of their relevance to the chemistry of some solar system objects, particularly of Io, the innermost of Jupiter''s Galilean satellites, that exhibits a surface very rich in frost SO2 and it is continuously bombarded with H+ ions caught in Jupiter''s magnetosphere. [Copyright &y& Elsevier]

Abstract: The Cassini Titan Radar Mapper observed on Titan several large features interpreted as cryovolcanic during the October 26, 2004 pass at high northern latitudes [Lopes, R.M.C., and 43 colleagues, 2007. Icarus 186, 395–412]. To date, models of ammonia-water resurfacing have not been tied to specific events or evolutionary stages of Titan. We propose a model of cryovolcanism that involves cracking at the base of the ice shell and formation of ammonia-water pockets in the ice. As these ammonia-water pockets undergo partial freezing in the cold ice shell, the ammonia concentration in the pockets increases, decreasing the negative buoyancy of the ammonia–water mixture. If the ice shell is contaminated by silicates delivered in impacts, the liquid–solid density difference would be even less. While the liquid cannot easily become buoyant relative to the surrounding ice, these concentrated ammonia-water pockets are sufficiently close to the neutral buoyancy point that large-scale tectonic stress patterns (tides, non-synchronous rotation, satellite volume changes, solid state convection, or subsurface pressure gradients associated with topography) would enable the ammonia to erupt effusively onto the surface. Rather than suggesting steady-state volcanism over the history of the Solar System, we favor a scenario where the cryovolcanic features could have been associated with episodic (potentially late) geological activity. [Copyright &y& Elsevier]

Abstract: We present high signal precision optical reflectance spectra of 2005 FY9 taken with the Red Channel Spectrograph and the 6.5-m MMT telescope on 2006 March 4 UT (5000–9500 Å; 6.33 Å pixel−1) and 2007 February 12 UT (6600–8500 Å; 1.93 Å pixel−1). From cross-correlation experiments between the 2006 March 4 spectrum and a pure CH4-ice Hapke model, we find the CH4-ice bands in the MMT spectrum are blueshifted by 3 ± 4 Å relative to bands in the pure CH4-ice Hapke spectrum. The higher resolution MMT spectrum of 2007 February 12 UT enabled us to measure shifts of individual CH4-ice bands. We find the 7296, 7862, and 7993 Å CH4-ice bands are blueshifted by 4 ± 2, 4 ± 4, and 6 ± 5 Å. From four measurements we report here and one of our previously published measurements, we find the CH4-ice bands are shifted by 4 ± 1 Å. This small shift is important because it suggest the presence of another ice component on the surface of 2005 FY9. Laboratory experiments show that CH4-ice bands in spectra of CH4 mixed with other ices are blueshifted relative to bands in spectra of pure CH4-ice. A likely candidate for the other component is N2-ice because its weak 2.15 μm band and blueshifted CH4 bands are seen in spectra of Triton and Pluto. Assuming the shift is due to the presence of N2, spectra taken on two consecutive nights show no difference in CH4/N2. In addition, we find no measurable difference in CH4/N2 at different depths into the surface of 2005 FY9. [Copyright &y& Elsevier]

Tracing measured compositions of comets to their origins continues to be of keen interest to cometary scientists and to dynamical modelers of Solar System formation and evolution. This requires building a taxonomy of comets from both present-day dynamical reservoirs: the Kuiper Belt (hereafter KB), sampled through observation of ecliptic comets (primarily Jupiter Family comets, or JFCs), and the Oort cloud (OC), represented observationally by the long-period comets and by Halley Family comets (HFCs). Because of their short orbital periods, JFCs are subjected to more frequent exposure to solar radiation compared with OC comets. The recent apparitions of the JFCs 9P/Tempel 1 and 73P/Schwassmann-Wachmann 3 permitted detailed observations of material issuing from below their surfaces—these comets added significantly to the compositional database on this dynamical class, which is under-represented in studies of cometary parent volatiles. This chapter reviews the latest techniques developed for analysis of high-resolution spectral observations from ∼2–5 μm, and compares measured abundances of native ices among comets. While no clear compositional delineation can be drawn along dynamical lines, interesting comparisons can be made. The sub-surface composition of comet 9P, as revealed by the Deep Impact ejecta, was similar to the majority of OC comets studied. Meanwhile, 73P was depleted in all native ices except HCN, similar to the disintegrated OC comet C/1999 S4 (LINEAR). These results suggest that 73P may have formed in the inner giant planets’ region while 9P formed farther out or, alternatively, that both JFCs formed farther from the Sun but with 73P forming later in time. [ABSTRACT FROM AUTHOR]

Abstract: The SWAN instrument observed the coma of Comet 9P/Tempel 1 at Lyman alpha around the Deep Impact event. From these observations, a water production rate profile for 3 weeks after the impact was derived. The comet could not be identified in images taken before the impact because of the relatively low production rates. The most important feature of the profile is that the production rate increases by about a factor of two more than a week after the impact. This is too late to be directly caused by the impact plume itself. Although it is not impossible that the impact triggered a resurfacing event, the comet is known to show sudden outburts, and the elevated production rate is similar to what has been reported on previous apparitions. [Copyright &y& Elsevier]

Abstract: By comparison with the Earth-like planets and the large icy satellites of the Solar System, one can model the internal structure of extrasolar planets. The input parameters are the composition of the star (Fe/Si and Mg/Si), the Mg content of the mantle (Mg#=Mg/[Mg+Fe]), the amount of H2O and the total mass of the planet. Equation of State (EoS) of the different materials that are likely to be present within such planets have been obtained thanks to recent progress in high-pressure experiments. They are used to compute the planetary radius as a function of the total mass. Based on accretion models and data on planetary differentiation, the internal structure is likely to consist of an iron-rich core, a silicate mantle and an outer silicate crust resulting from magma formation in the mantle. The amount of H2O and the surface temperature control the possibility for these planets to harbor an ocean. In preparation to the interpretation of the forthcoming data from the CNES led CoRoT (Convection Rotation and Transit) mission and from ground-based observations, this paper investigates the relationship between radius and mass. If H2O is not an important component (less than 0.1%) of the total mass of the planet, then a relation is calculated with and for and , respectively. Calculations for a planet that contains 50% H2O suggest that the radius would be more than 25% larger than that based on the Earth-like model, with for and for , respectively. For a surface temperature of 300 K, the thickness of the ocean varies from 150 to 50 km for planets 1 to 10 times the Earth''s mass, respectively. Application of this algorithm to bodies of the Solar System provides not only a good fit to most terrestrial planets and large icy satellites, but also insights for discussing future observations of exoplanets. [Copyright &y& Elsevier]

Abstract: Recent attempts using high resolution spectra to detect N+ 2 in several comets were unsuccessful [Cochran, A.L., Cochran, W.D., Baker, E.S., 2000. Icarus 146, 583–593; Cochran, A.L., 2002. Astrophys. J. 576, L165–L168]. The upper limits on N+ 2 in comparison with the positively detected CO+ for Comets C/1995 O1 Hale–Bopp, 122P/1995 S1 de Vico and 153P/2002 C1 Ikeya–Zhang range between . Ar was not detected in three recent comets [Weaver, H.A., Feldman, P.D., Combi, M.R., Krasnopolsky, V., Lisse, C.M., Shemansky, D.E., 2002. Astrophys. J. 576, L95–L98], with upper limits of for Comets C/1999 T1 McNaught–Hartley, C/2001 A2 LINEAR and C/2000 WM1 LINEAR. The Ar detected by Stern et al. [Stern, S.A., Slater, D.C., Festou, M.C., Parker, J.Wm., Gladstone, G.R., A''Hearn, M.F., Wilkinson, E., 2000. Astrophys. J. 544, L169–L172] for Comet C/1995 O1 Hale–Bopp, gives a ratio , which was not confirmed by Cosmovici et al. [Cosmovici, C.B., Bratina, V., Schwarz, G., Tozzi, G., Mumma, M.J., Stalio, R., 2006. Astrophys. Space Sci. 301, 135–143]. Trying to solve the two problems, we studied experimentally the trapping of in amorphous water ice, at 24–30 K. CO was found to be trapped in the ice 20–70 times more efficiently than N2 and with the same efficiency as Ar. The resulting Ar/CO ratio of is consistent with Weaver et al.''s [Weaver, H.A., Feldman, P.D., Combi, M.R., Krasnopolsky, V., Lisse, C.M., Shemansky, D.E., 2002. Astrophys. J. 576, L95–L98] non-detection of Ar. However, with an extreme starting value for N2/CO=0.22 in the region where the ice grains which agglomerated to produce comet nuclei were formed, the expected N2/CO ratio in the cometary ice should be , much higher than its non-detection limit. [Copyright &y& Elsevier]

Abstract: Although water- and ammonia-ices have been observed or postulated as important components of the icy surfaces of planetary satellites in the outer Solar System, significant gaps exist in our knowledge of the spectra and behavior of such mixtures under astrophysical conditions. To that end, we have completed low-temperature spectroscopic studies (1–20 μm) of water–ammonia mixtures, with an emphasis on features in the near-IR, a region which is accessible to ground-based observations. The influences of composition, formation temperature, thermal- and radiation-processing, and phase (crystalline or amorphous) of the components were examined. Spectra of both pure NH3 and H2O–NH3 icy mixtures with ratios from 0.7 to 57 were measured at temperatures from 10 to 120 K. Conditions for the formation and thermal stability of the ammonia hemihydrate (2NH3⋅H2O) and the ammonia monohydrate (NH3⋅H2O) have been examined. Band positions of NH3 in different H2O-ices and major band positions of the hydrates were measured. We report spectral shifts that depend on concentration and temperature. The radiation-induced amorphization of the hemihydrate was observed and the radiation destruction of NH3 in H2O-ices was measured. Implications of these results for the formation, stability, and detection of ammonia on outer satellite surfaces are discussed. [Copyright &y& Elsevier]

Abstract: We report the rates of decomposition by ultraviolet (UV) photolysis of four amino acids in millimeter-thick crystalline water ice matrices at 100 K to constrain the survivability of these important organic molecules within ice lying near the surfaces of outer Solar System bodies. We UV-irradiated crystalline ice samples containing known concentrations of the amino acids glycine, aspartic acid, glutamic acid, and phenylalanine, then we measured the surviving concentrations using high performance liquid chromatography (HPLC) with fluorescence detection. From these experiments, we determine photolytic decomposition rates and half-lives. The half-life varies linearly with the ice thickness for all acids studied here. For example, glycine is the most resistant to photolytic destruction with a half-life of 50, 12, and 3.7 h in 1.6, 0.28, and 0.14 mm thick ices, respectively. We explain this linear variation of half-life with thickness as a consequence of extinction, mostly due to scattering, within these macroscopically thick ice samples. Applied to low latitude surface ice on Jupiter''s satellite Europa, this analysis indicates that the concentration of any of these amino acids within the top meter of similar ice will be halved within a ∼10 year timescale. [Copyright &y& Elsevier]

Abstract: Icy surfaces like the polar caps of Mars, comets, Edgeworth–Kuiper belt objects or the surface areas of many moons in the outer Solar System behave different than rock and soil surfaces when irradiated by solar light. The latter ones absorb and reflect incoming solar radiation immediately at the surface. In contrast, ices are partially transparent in the visible spectral range and opaque in the infrared. Due to this fact it is possible for the solar radiation to reach a certain depth and increase the temperature of the sub-surface layers directly. This internal temperature rise is called “solid-state greenhouse effect,” in analogy to the classical greenhouse effect in an atmosphere. It may play an important role in the energy balance of various icy bodies in the Solar System. Within the scope of a project conducted at the Space Research Institute of the Austrian Academy of Sciences in Graz the solid-state greenhouse effect was investigated experimentally and theoretically. A number of experiments with diverse materials, focussing mainly on layered samples with a surface cover consisting of transparent H2O-ice, were performed. The samples were irradiated under cryo-vacuum conditions by a solar simulator. The temperature distributions inside the samples were measured and compared with the results of numerical model calculations. We found that the predicted sub-surface temperature maximum is very clearly measurable in glass beads samples with various particle size distributions, but can also be detected in transparent compact surface ice layers. However, in the latter case it is less distinct than originally expected. Measuring the effect by laboratory methods turned out to be a difficult task due to the shallow depth where the temperature maximum occurs. [Copyright &y& Elsevier]

Abstract: We present 0.8–2.4 μm spectral observations of uranian satellites, obtained at IRTF/SpeX on 17 nights during 2001–2005. The spectra reveal for the first time the presence of CO2 ice on the surfaces of Umbriel and Titania, by means of 3 narrow absorption bands near 2 μm. Several additional, weaker CO2 ice absorptions have also been detected. No CO2 absorption is seen in Oberon spectra, and the strengths of the CO2 ice bands decline with planetocentric distance from Ariel through Titania. We use the CO2 absorptions to map the longitudinal distribution of CO2 ice on Ariel, Umbriel, and Titania, showing that it is most abundant on their trailing hemispheres. We also examine H2O ice absorptions in the spectra, finding deeper H2O bands on the leading hemispheres of Ariel, Umbriel, and Titania, but the opposite pattern on Oberon. Potential mechanisms to produce the observed longitudinal and planetocentric distributions of the two ices are considered. [Copyright &y& Elsevier]

Abstract: We have found that 0.8 MeV proton irradiation of crystalline H2O–ice results in temperature dependent amorphization. The H2O–ice''s phase was determined using the near infrared spectrum from 1.0 μm (10,000 cm−1) to 2.5 μm (4000 cm−1). In crystalline H2O–ice, the 1.65-μm (6061 cm−1) band is strong while it is nearly absent in the amorphous spectrum [Schmitt, B., Quirico, E., Trotta, F., Grundy, W.M., 1998. In: Schmitt, B., de Bergh, C., Festou, M. (Eds.), Solar System Ices. Kluwer Academic, Norwell, MA, 1998, pp. 199–240]. In this experiment, at low temperatures (9, 25, and 40 K), irradiation of crystalline H2O–ice produced the amorphous H2O–ice''s spectrum. However, at 50 K, some crystalline absorptions persisted after irradiation and at 70 and 100 K the crystalline spectrum showed only slight changes after irradiation. Our results agree with previous H2O–ice irradiation studies examining the crystalline peaks near 44 and 62 μm by Moore and Hudson [Moore, M.H., Hudson, R.L., 1992. Astrophys. J. 401, 353–360] and near 3.07 μm by Strazzulla et al. [Strazzulla, G., Baratta, G.A., Leto, G., Foti, G., 1992. Europhys. Lett. 18, 517–522] and by Leto and Baratta [Leto, G., Baratta, G.A., 2003. Astron. Astrophys. 397, 7–13]. We present a method of measuring band areas to quantify the phase and radiation dose of icy Solar System surfaces. [Copyright &y& Elsevier]