We present the first map of CO2 at the surface of Enceladus using data obtained by the Cassini Visible-Infrared Mapping Spectrometer (VIMS). In order to measure the weak and narrow CO2 absorption band depths around 4.26 gm, we improved: (1) the calibration of VIMS spectra; (2) the calculation of geographic coordinates; and (3) the projection techniques. We averaged multiple observations of a given area to obtain a signal to noise ratio high enough to map the CO2 abundances. CO2 is reliably detected mostly in the South Polar Region. This region includes active faults (Tiger Stripes), the highest observed surface temperatures, and locations of active plume eruptions. The occurrence here of CO2 is consistent with an endogenic origin controlled by tectonics. Both pure CO2 ice and complexed CO2 are detected from the positions of absorption bands between 4.27 and 4.24 mu m. The highest concentrations of CO2 are between the main active faults of the South Polar Region, where the surface temperature is low. Pure CO2 ice deposits at the surface of Enceladus are best modeled by the formation of gas pockets below the icy crust and above the surface of the internal ocean. These pockets eventually release cold CO2 gas ( similar to 70 to similar to 119 K) at low-velocity (seeping) between the Tiger Stripes [Matson et al., 2018, Icarus, 302, 18 similar to 26]. CO2 clathrate hydrates may form in the ocean and may be subsequently released when a CO2 gas pocket blows out and erupts. Other mechanisms may contribute to reinforcing the anti-correlation of the CO2 distribution (of any type) with respect to the location of the Tiger Stripes, such as successive sublimation of CO2 and condensation on colder areas, and partial frost cover by H2O releases from plume eruptions.

Solid CO2 surface deposits were reported in Enceladus' South Polar Region by Brown et al. (2006). They noted that such volatile deposits are temporary and posited ongoing replenishment. We present a model for this replenishment by expanding on the Matson et al. (2012) model of subsurface heat and chemical transport in Enceladus. Our model explains the distributions of both CO2 frost and complexed CO2 clathrate hydrate as seen in the Cassini Visual and Infrared Mapping Spectrometer (VIMS) data. We trace the journey of CO2 from a subsurface ocean. The ocean-water circulation model of Matson et al. (2012) brings water up to near the surface where gas exsolves to form bubbles. Some of the CO2 bubbles are trapped and form pockets of gas in recesses at the bottom of the uppermost ice layer. When fissures break open these pockets, the CO2 gas is vented. Gas pocket venting is episodic compared to the more or less continuous eruptive plumes, emanating from the "tiger stripes", that are supported by plume chambers. Two styles of gas pocket venting are considered: (1) seeps, and (2) blowouts. The presence of CO2 frost patches suggests that the pocket gas slowly seeped through fractured, cold ice and when some of the gas reached the surface it was cold enough to condense (i.e., T similar to 70 to similar to 119 K). If the fissure opening is large, a blowout occurs. The rapid escape of gas and drop in pocket pressure causes water in the pocket to boil and create many small aerosol droplets of seawater. These may be carried along by the erupting gas. Electrically charged droplets can couple to the magnetosphere, and be dragged away from Enceladus. Most of the CO2 blowout gas escapes from Enceladus and the remainder is distributed globally. However, CO2 trapped in a clathrate structure does not escape. It is much heavier and slower moving than the CO2 gas. Its motion is ballistic and has an average range of about 17 km. Thus, it contributes to deposits in the vicinity of the vent. Local heat flow indicates that gas pockets can be located as deep as several tens of meters below the surface. Gas pockets can be reused, and we explore their life cycle. (C) 2017 Elsevier Inc. All rights reserved.

Analysis of Galileo Near-Infrared Mapping Spectrometer observations of Marduk Fluctus, a volcano on the Jovian moon lo, reveals a style of volcanic activity not previously seen there-a powerful thermal event lasting only a few minutes in 1996. The thermal emission rapidly fades, suggesting extremely rapid cooling of small clasts. The duration and evolution of the explosive eruption are akin to what might be expected from a strombolian or vulcanian explosion. The presence of such events provides an additional volcanic process that can be imaged by future missions with the intent of determining lava composition from eruption temperature, an important constraint on the internal composition of lo. These data promise to be of particular use in understanding the mechanics of explosive volcanic processes on lo.

To date, there has been no conclusive observation of ongoing endogenous volcanic activity on Saturn's moon Titan. However, with time, Titan's atmospheric methane is lost and must be replenished. We have modeled one possible mechanism for the replenishment of Titan's methane loss. Cryolavas can supply enough heat to release large amounts of methane from methane clathrate hydrates (MCH). The volume of methane released is controlled by the flow thickness and its areal extent. The depth of the destabilisation layer is typically approximate to 30% of the thickness of the lava flow (approximate to 3 m for a 10-m thick flow). For this flow example, a maximum of 372 kg of methane is released per m(2) of flow area. Such an event would release methane for nearly a year. One or two events per year covering similar to 20 km(2) would be sufficient to resupply atmospheric methane. A much larger effusive event covering an area of approximate to 9000 km(2) with flows 200 m thick would release enough methane to sustain current methane concentrations for 10,000 years. The minimum size of "cryo-flows" sufficient to maintain the current atmospheric methane is small enough that their detection with current instruments (e.g., Cassini) could be challenging. We do not suggest that Titan's original atmosphere was generated by this mechanism. It is unlikely that small-scale surface MCH destabilisation is solely responsible for long-term (> a few Myr) sustenance of Titan's atmospheric methane, but rather we present it as a possible contributor to Titan's past and current atmospheric methane. (C) 2016 Published by Elsevier Inc.

We identify nine new faint thermal sources on Io via color ratio images constructed from relatively high spatial resolution Galileo NIMS data acquired late in the mission. All of these identifications are associated with small dark paterae. We utilize NIMS data to quantify their volcanic thermal emission as similar to 0.53 x 10(12) W (or similar to 0.5% of Io's total heat flow). In addition, we refine our previous estimates of the thermal emission from 47 hot spots and highlight several hot spots within the Amirani flow field.Small dark paterae still out-number faint (close to the limit of detection) hot spots identified in high spatial resolution multi-wavelength NIMS data. In particular, we point out 24 small dark paterae that were scanned by NIMS (at resolutions down to similar to 17 km/pixel) but had no detectable volcanic thermal emission. All dark paterae are expected to have some volcanic thermal emission, but the small size and finite number of detectable faint sources limit their contribution to the total heat flow on Io. Compared to small paterae, small dark flows are more numerous but must have significantly lower surface temperatures.Finally, we update and summarize our results for the global heat flow on lo due to 242 recently active volcanic features including other dark paterae as well as large dark flows. The volcanic thermal emission from known hot spots, undetected (scanned) dark patera and outbursts can account for only similar to 56.2 x 10(12)W (or similar to 54%) of Io's total heat flow. Approximately 49 x 10(12)W (or similar to 46%) of la's heat flow remains an enigma. (C) 2014 Elsevier Inc. All rights reserved.

We present a map of Io's volcanic heat flow. Io's high heat flow is a result of intense tidal heating, which generates widespread volcanic activity. The surface expression of ongoing volcanic activity constrains the location and magnitude of tidal dissipation within Io. Tidal heating models place heating either at relatively shallow (aesthenosphere) levels, or deep in the mantle. It was thought that actual tidal heating could be approximated using a combination of these end-member models. Io's volcanic heat flow has now been mapped in sufficient detail to compare with the models. Our maps show that the distribution of heat flow is not matched by current models of deep nor shallow tidal heating, nor by any combination of these two models. We find relatively low heat flow at sub-jovian (0 degrees W) and anti-jovian (180 degrees W) longitudes, at odds with the pure aesthenospheric heating model. Furthermore, there are large swaths of Io's surface where there is poor correlation between the number of hot spots in an area and the power emitted. We have previously accounted for approximate to 54% of Io's observed heat flow. We now show that Io's anomalously warm poles, possibly the result of heat flow from deep-mantle heating, would yield the "missing" energy (48 TW) if the polar surfaces are at temperatures of similar to 90 K to similar to 95 K and cover latitudes above similar to 43 degrees to similar to 48 degrees respectively. This possibility implies a ratio of deep to shallow heating of about 1:1. However, explaining regional variations in surface volcanic activity requires more detailed modeling of the location and magnitude of the internal tidal dissipation and the consequences of mantle convection and advection within Io. Future model predictions can be compared to our heat flow map. (C) 2015 Elsevier Inc. All rights reserved.

Ganymede and Callisto are planet-sized moons of Jupiter, with surfaces composed of a mixture of dark dust and bright ice. Similar in size, they both have interiors of half ice and half rock/metal, but Ganymede's interior appears to be segregated by density, while Callisto's interior is mostly mixed. Both moons appear to have subsurface liquid water oceans sandwiched between low-pressure surface ice and high-pressure ice phases deep in their interiors. Ganymede has an intrinsic magnetic field, probably generated by dynamo action in a molten iron core. The surface of Callisto and part of the surface of Ganymede appear to be ancient, dominated by impact cratering and the slow decay of ice sublimating into the surrounding vacuum, leaving behind dark dust. Two-thirds of Ganymede's surface was rejuvenated during a dramatic event at some point in the middle of solar system history, by intense extensional tectonism and possibly cryovolcanism.

We have used recent surveys of the composition of exoplanet host stars to investigate the expected composition of condensed material in planetesimals formed beyond the snow line in the circumstellar nebulae of these systems. Of the major solid-forming elements, C and O abundances (and particularly the C/O abundance ratio) strongly affect the amounts of volatile ices and refractory phases in icy planetesimals formed in these systems. This results from these elements' effects on the partitioning of O among gas, refractory solid and ice phases in the final condensate. The calculations use a self-consistent model for the condensation sequence of volatile ices from the nebula gas after refractory (silicate and metal) phases have condensed. The resultant mass fractions (compared to the total condensate) of refractory phases and ices were calculated for a range of nebular temperature structures and redox conditions. Planetesimals in systems with sub-solar C/O should be water ice-rich, with lower than solar mass fractions of refractory materials, while in super-solar C/O systems planetesimals should have significantly higher mass fractions of refractories, in some cases having little or no water ice. C-bearing volatile ices and clathrates also become increasingly important with increasing C/O depending on the assumed nebular temperatures. These compositional variations in early condensates in the outer portions of the nebula will be significant for the equivalent of the Kuiper Belt in these systems, icy satellites of giant planets, and the enrichment (over stellar values) of volatiles and heavy elements in giant planet atmospheres.

The eruptive plumes and large heat flow (∼15GW) observed by Cassini in the South Polar Region of Enceladus may be expressions of hydrothermal activity inside Enceladus. We hypothesize that a subsurface ocean is the heat reservoir for thermal anomalies on the surface and the source of heat and chemicals necessary for the plumes. The ocean is believed to contain dissolved gases, mostly CO2 and is found to be relatively warm (∼0°C). Regular tidal forces open cracks in the icy crust above the ocean. Ocean water fills these fissures. There, the conditions are met for the upward movement of water and the dissolved gases to exsolve and form bubbles, lowering the bulk density of the water column and making the pressure at its bottom less than that at the top of the ocean. This pressure difference drives ocean water into and up the conduits toward the surface. This transportation mechanism supports the thermal anomalies and delivers heat and chemicals to the chambers from which the plumes erupt. Water enters these chambers and there its bubbles pop and loft an aerosol mist into the ullage. The exiting plume gas entrains some of these small droplets. Thus, nonvolatile chemical species in ocean water can be present in the plume particles. A CO2 equivalent-gas molar fraction of ∼4×10−4 for the ocean is sufficient to support the circulation. A source of heat is needed to keep the ocean warm at ∼0°C (about two degrees above its freezing point). The source of heat is unknown, but our hypothesis is not dependent on any particular mechanism for producing the heat.

Using the NIMS Io Thermal Emission Database (NITED), a collection of over 1000 measurements of radiant flux from Io’s volcanoes (Davies, A.G. et al. [2012]. Geophys. Res. Lett. 39, L01201. doi:10.1029/2011GL049999), we have examined the variability of thermal emission from three of Io’s volcanoes: Pele, Janus Patera and Kanehekili Fluctus. At Pele, the 5-μm thermal emission as derived from 28 night time observations is remarkably steady at 37±10GWμm−1, re-affirming previous analyses that suggested that Pele an active, rapidly overturning silicate lava lake. Janus Patera also exhibits relatively steady 5-μm thermal emission (≈20±3GWμm−1) in the four observations where Janus is resolved from nearby Kanehekili Fluctus. Janus Patera might contain a Pele-like lava lake with an effusion rate (QF) of ≈40–70m3s−1. It should be a prime target for a future mission to Io in order to obtain data to determine lava eruption temperature. Kanehekili Fluctus has a thermal emission spectrum that is indicative of the emplacement of lava flows with insulated crusts. Effusion rate at Kanehekili Fluctus dropped by an order of magnitude from ≈95m3s−1 in mid-1997 to ≈4m3s−1 in late 2001.

We have examined thermal emission from 240 active or recently-active volcanic features on Io and quantified the magnitude and distribution of their volcanic heat flow during the Galileo epoch. We use spacecraft data and a geological map of Io to derive an estimate of the maximum possible contribution from small dark areas not detected as thermally active but which nevertheless appear to be sites of recent volcanic activity. We utilize a trend analysis to extrapolate from the smallest detectable volcanic heat sources to these smallest mapped dark areas. Including the additional heat from estimates for "outburst" eruptions and for a multitude of very small ("myriad") hot spots, we account for similar to 62 x 10(12) W (similar to 59 +/- 7% of Io's total thermal emission). Loki Patera contributes, on average, 9.6 x 10(12) W (similar to 9.1 +/- 1%). All dark paterae contribute 45.3 x 10(12) W (similar to 43 +/- 5%). Although dark flow fields cover a much larger area than dark paterae, they contribute only 5.6 x 10(12) W (similar to 5.3 +/- 0.6%). Bright paterae contribute similar to 2.6 x 10(12) W (similar to 2.5 +/- 0.3%). Outburst eruption phases and very small hot spots contribute no more than similar to 4% of Io's total thermal emission: this is probably a maximum value. About 50% of Io's volcanic heat flow emanates from only 1.2% of Io's surface. Of Io's heat flow, 41 +/- 7.0% remains unaccounted for in terms of identified sources. Globally, volcanic heat flow is not uniformly distributed. Power output per unit surface area is slightly biased towards mid-latitudes, although there is a stronger bias toward the northern hemisphere when Loki Patera is included. There is a slight favoring of the northern hemisphere for outbursts where locations were well constrained. Globally, we find peaks in thermal emission at similar to 315 degrees W and similar to 105 degrees W (using 30 degrees bins). There is a minimum in thermal emission at around 200 degrees W (almost at the anti-jovian longitude) which is a significant regional difference. These peaks and troughs suggest a shift to the east from predicted global heat flow patterns resulting from tidal heating in an asthenosphere. Global volcanic heat flow is dominated by thermal emission from paterae, especially from Loki Patera (312 degrees W, 12 degrees N). Thermal emission from dark flows maximises between 165 degrees W and 225 degrees W. Finally, it is possible that a multitude of very small hot spots, smaller than the present angular resolution detection limits, and/or cooler, secondary volcanic processes involving sulphurous compounds, may be responsible for at least part of the heat flow that is not associated with known sources. Such activity should be sought out during the next mission to Io. (c) 2012 Elsevier Inc. All rights reserved.

Motivated by recent spectroscopic observations suggesting that atmospheres of some extrasolar giant planets are carbon-rich, i.e., carbon/oxygen ratio (C/O) >= 1, we find that the whole set of compositional data for Jupiter is consistent with the hypothesis that it should be a carbon-rich giant planet. We show that the formation of Jupiter in the cold outer part of an oxygen-depleted disk (C/O similar to 1) reproduces the measured Jovian elemental abundances at least as well as the hitherto canonical model of Jupiter formed in a disk of solar composition (C/O = 0.54). The resulting O abundance in Jupiter's envelope is then moderately enriched by a factor of similar to 2 x solar (instead of similar to 7 x solar) and is found to be consistent with values predicted by thermochemical models of the atmosphere. That Jupiter formed in a disk with C/O similar to 1 implies that water ice was heterogeneously distributed over several AU beyond the snow line in the primordial nebula and that the fraction of water contained in icy planetesimals was a strong function of their formation location and time. The Jovian oxygen abundance to be measured by NASA's Juno mission en route to Jupiter will provide a direct and strict test of our predictions.

The recent inference of a carbon-rich atmosphere, with C/O >= 1, in the hot Jupiter WASP-12b motivates the exotic new class of carbon-rich planets (CRPs). We report a detailed study of the atmospheric chemistry and spectroscopic signatures of carbon-rich giant planets (CRGs) and the compositions of icy planetesimals required for their formation, and the apportionment of ices, rock, and volatiles in their envelopes. For C/O >= 1, most of the atmospheric oxygen is occupied by CO for T > 1400 K and pressure (P) < 1 bar, causing a substantial depletion in H2O, and an overabundance of CH4 compared to those obtained by assuming solar abundances (C/O = 0.54) in chemical equilibrium. These differences in chemistry cause distinctly observable signatures in spectra. We also find that a C/O >= 1 strongly depletes the abundances of TiO and VO available to form thermal inversions, which is adequate to rule out thermal inversions due to TiO/VO even in the most highly irradiated hot Jupiters, such as WASP-12b. Adopting stellar abundances (C/O = 0.44) for the primordial disk composition and low-temperature formation conditions (T <= 30 K) for WASP-12b leads to a C/O ratio of 0.27 in accreted planetesimals, and, consequently, in the planet's envelope. In contrast, a C/O ratio of 1 in the envelope of WASP-12b requires a substantial depletion of oxygen in the disk, by a factor of 0.41 for the same formation conditions. This scenario also satisfies the constraints on the C/H and O/H ratios reported for WASP-12b. If, alternatively, hotter conditions prevailed in a stellar composition disk such that only H2O is condensed, the remaining gas can potentially have a C/O 1. However, a high C/O in WASP-12b caused predominantly by gas accretion would preclude super-stellar C/H ratios which also fit the data.