Volatile Transport Research Articles

The CO-fuelled Time Machine: tracing birth conditions and Terrestrial Planet Formation Outcomes in HD 163296 through Pebble Drift-induced CO Enhancements

ABSTRACT The architecture and composition of planetary systems are thought to be strongly influenced by the transport and delivery of dust and volatiles via ices on pebbles during the planet formation phase in protoplanetary discs. Understanding these transport mechanisms is crucial in building a comprehensive picture of planet formation, including material and chemical budget; constraining the birth properties of these discs is a key step in this process. We present a novel method of retrieving such properties by studying the transport of icy pebbles in the context of an observed gas-phase CO enhancement within the CO snowline in the protoplanetary disc around HD 163296. We combine Markov Chain Monte Carlo sampling with a fast model of radial drift to determine the birth gas mass and characteristic radius of the disc, and compare our results against observations and models in the literature; we find the birth-condition disc gas mass to be $\log _{10}(M_{\rm {disc}}/\mathrm{ M}_{\odot })=-0.64^{+0.19}_{-0.24}$ and the characteristic radius to be $\log _{10}(r_{\rm {c}}/\rm {au})=2.30^{+0.45}_{-0.46}$. We additionally determine that dust grains must be ‘fragile’ ($v_{\mathrm{ f}}=100~\mathrm{cms}^{-1}$) to retain enough dust to match current dust mass observations, with our lowest fragmentation velocity model providing a current-age dust mass of $\rm {\mathit{ M}_{dust}}=662^{+518}_{-278}\, \rm {M_{\rm{\oplus}}}$ based on the retrieved birth conditions. Using our retrieved birth conditions, we extend our simulations to mass of material reaching the water snowline in the inner disc, where terrestrial and super-Earth planets may be forming, and speculate on the nature of these exoplanets.

The Formation of K-Cymrite in Subduction Zones and Its Potential for Transport of Potassium, Water, and Nitrogen into the Mantle

The conditions of the formation of K-cymrite in volatile-rich pelite and partially devolatilized mica quartz–muscovite–chlorite schist were experimentally investigated at pressures of 5.5, 6.3, and 7.8 GPa and temperatures ranging from 900 to 1090°C corresponding to hot subduction geotherm. Experimental samples at these P–T conditions formed assemblage of solid phases (Grt + Coe + Phe + Cpx + Ky, with accessory Po + Ru + Zrn ± Mnz) and water-enriched supercritical fluid–melt. Analysis of the obtained data indicates that the stability of phengite and its potential replacement by K-cymrite depends on the P–T conditions and the amount of volatiles in the metasediment. In samples of volatile-rich pelite and mica schist at 5.5 GPa and 900°C, as well as at 6.3 GPa and 1000°C, phengite remains stable in equilibrium with 3–13 wt % of the fluid–melt. With increasing pressure up to 7.8 GPa and temperature up to 1090°C, the fraction of supercritical fluid–melt in pelite reaches 20 wt %, while phengite disappears. Only 5 wt % supercritical fluid–melt are formed in the schist at 7.8 GPa and 1070°C, while most part of phengite is preserved. For the first time, phase assemblage with phengite and K-cymrite (±kokchetavite) was obtained in the pelite and schist samples at 7.8 GPa and 1070°C. The assemblage was identified using Raman mapping. At stepwise devolatilization (with removal of fluid–melt portion forming in equilibrium with volatile-bearing minerals that are stable at P–T conditions of experiments), phengite has been preserved up to 7.8 GPa and 1090°C, but K-cymrite is not formed in the absence of fluid–melt. It was concluded that the most effective transport of volatiles (first of all, water) in the metasediment to depths over 240 km may occur during its partial and early (before the formation of supercritical fluid–melt) devolatilization. In this case, almost all phengite may reach depths of 240 km during metasediment subduction and then transform into water-bearing K-cymrite, or, in the presence of nitrogen in the metasediment, into nitrogen-bearing K-cymrite, thus facilitating the further transport of LILE (large-ion lithophile elements), water, and nitrogen. However, the formation of a significant portion of supercritical fluid–melt leads to the complete dissolution of phengite with increasing P–T conditions, making further transport of LILE, water, and nitrogen impossible. During deep multi-stage devolatilization, phengite remains stable up to depths of 240 km; however, during further subduction, it likely transforms into an anhydrous K-hollandite (KAlSi3O8).

Helium and carbon isotope compositions of thermal fluids in the northeastern Anatolia: Implications for the heat source and volatile flux

In this study, we make a quantitative assessment on the volatile flux of mantle-derived fluids and source of volatiles to explain the geologic controls on the transport of volatiles within thermal fluids of northeastern Anatolia. In line with this objective, we collected 22 samples (gas and water phase) from 16 geothermal fields in NE Turkey covering an area of nearly 100,000 km2 that extends from the eastern termination of North Anatolian Fault towards the Georgian and Armenian borders. The 3He/4He ratios of the samples (R) normalized to the atmospheric 3He/4He ratio (Ra = 1.4 × 10−6) vary from 0.31 to 7.15, and are considerably higher than the crustal value of 0.02Ra. Regarding spatial distribution of helium isotope composition, samples collected from areas of tectonic unrest around the Erzincan and Erzurum pull-apart basins in the southern part are represented by a higher range of 3He/4He ratios (>5 Ra) than those in volcanic areas to the east and northeast of the region. δ13CCO2 values of the gas samples varying from −20.76 to 5.43 ‰ are about 4–5 ‰ lower than δ13CDIC values of the water samples that range from −16.90 to 8.85 ‰, indicating CO2 removal from waters by degassing. CO2/3He ratios of gas samples falling in the range of 3.81 × 109 to 2.83 × 1012 imply that carbon is derived from the mixing between the crustal lithologies and mantle, the latter having a contribution up to 40 %. The maximum flux of mantle-derived fluids is found 88 mm/a at Erzincan (eastern part of the North Anatolian Fault Zone). This value is higher by a factor of about 10 than the western part of the fault zone. Calculations show that degassing from magmatic bodies is the sole mechanism to explain the high helium isotope compositions in the region. Therefore, we suggest that mantle-derived He contents might be due to extensive melting associated with active tectonism. The 3He/Heat ratios of thermal waters in northeastern Turkey were calculated in range of 0.25 to 29.7 × 10−15 cm3(STP)/J, consistent with the data reported for waters along the North Anatolian Fault, indicating a crustal heat source for the geothermal systems in northeastern Turkey.

How obliquity has differently shaped Pluto’s and Triton’s landscapes and climates

Triton and Pluto are believed to share a common origin, both forming initially in the Kuiper Belt but Triton being later captured by Neptune. Both objects display similar sizes, densities, and atmospheric and surface ice composition, with the presence of volatile ices N2, CH4, and CO. Yet their appearance, including their surface albedo and ice distribution strongly differ. What can explain these different appearances? A first disparity is that Triton is experiencing significant tidal heating due to its orbit around Neptune, with subsequent resurfacing and a relatively flat surface, while Pluto is not tidally activated and displays a pronounced topography. Here we present long-term volatile transport simulations of Pluto and Triton, using the same initial conditions and volatile inventory, but with the known orbit and rotation of each object. The model reproduces, to first order, the observed volatile ice surface distribution on Pluto and Triton. Our results unambiguously demonstrate that obliquity is the main driver of the differences in surface appearance and in climate properties on Pluto and Triton, and give further support to the hypothesis that both objects had a common origin followed by a different dynamical history.

Volatile Transport on Ariel and Implications for the Origin and Distribution of Carbon Dioxide on Uranian Moons

Volatile Transport on Ariel and Implications for the Origin and Distribution of Carbon Dioxide on Uranian Moons

Evaluating the Use of Seasonal Surface Displacements and Time‐Variable Gravity to Constrain the Interior of Mars

AbstractThe mass transport of volatiles on Mars represents a seasonally changing load on the surface of the planet. Like on Earth, as mass is redistributed across the planet, the surface responds in a complex manner becoming displaced downwards or upwards. The magnitude and extent of displacement depend on the properties of the load and mechanical properties of the planetary interior. Based on new estimates of the height variation of the seasonal polar caps (SPCs), we predict local surface displacements of up to tens of millimeters with a strong degree 1 signal throughout the Martian year. The long‐wavelength portion of the displacement is potentially observable, with a magnitude of a few millimeters, located away from the SPC where one could realistically measure it with a landed or orbital mission. We also model the direct contribution of this process to observable time variable gravity, where we find the zonal coefficients to be in line with previous measurements, although with a smaller magnitude. Future measurements of this displacement could be used to help elucidate the composition of the interior of Mars using this process as a probe into the Martian interior. Furthermore, more refined measurements of time‐variable gravity would be a powerful tool in constraining the pole‐to‐pole volatile cycle present on Mars.

Initial atmospheric conditions control transport of volcanic volatiles, forcing and impacts

Abstract. Volcanic eruptions impact the climate and environment. The volcanic forcing is determined by eruption source parameters, including the mass and composition of volcanic volatiles, eruption season, eruption latitude, and injection altitude. Moreover, initial atmospheric conditions of the climate system play an important role in shaping the volcanic forcing and response. However, our understanding of the combination of these factors, the distinctions between tropical and extratropical volcanic eruptions, and the co-injection of sulfur and halogens remains limited. Here, we perform ensemble simulations of volcanic eruptions at 15 and 64° N in January, injecting 17 Mt of SO2 together with HCl and HBr at 24 km altitude. Our findings reveal that initial atmospheric conditions control the transport of volcanic volatiles from the first month and modulate the subsequent latitudinal distribution of sulfate aerosols and halogens. This results in different volcanic forcing, surface temperature and ozone responses over the globe and Northern Hemisphere extratropics (NHET) among the model ensemble members with different initial atmospheric conditions. NH extratropical eruptions exhibit a larger NHET mean volcanic forcing, surface cooling and ozone depletion compared with tropical eruptions. However, tropical eruptions lead to more prolonged impacts compared with NH extratropical eruptions, both globally and in the NHET. The sensitivity of volcanic forcing to varying eruption source parameters and model dependency is discussed, emphasizing the need for future multi-model studies to consider the influence of initial conditions and eruption source parameters on volcanic forcing and subsequent impacts.

Evaluation of agile attributes for low-cost carriers to achieve sustainable development using an integrated MCDM approach

PurposeSince conducting agile strategies provides sustainable passenger satisfaction and revenue by replacing applied policies with more profitable ones rapidly, the focus of this study is to evaluate agile attributes for managing low-cost carriers (LCCs) operations by means of resources and competences based on dynamic capabilities built on resource-based view (RBV) theory and to achieve sustainable competitive advantage in a volatile and dynamic air transport environment. LCCs in Turkey are also evaluated in this study since the competition among LCCs is high to gain market share and they can adapt quickly to all kinds of circumstances.Design/methodology/approachTwo well-known Multi-Criteria Decision-Making Methods (MCDM) named as the Stepwise Weight Assessment Ratio Analysis (SWARA) and multi-attributive border approximation area comparison (MABAC) methods by employing Picture fuzzy sets (PiFS) are employed to determine weight of agile attributes and superiority of LCCs based on agile attributes in the market, respectively. To check the consistency and robustness of the results for the proposed approach, comparative and sensitivity analysis are performed at the end of the study.FindingsWhile the ranking orders of agile attributes are Strategic Responsiveness (AG1), Financial Management (AG4), Quality (AG2), Digital integration (AG3) and Reliability (AG5), respectively, LCC2 is selected as the best agile airline company in Turkey with respect to agile attributes. SWARA and MABAC method based on PiFS is appropriate and effective method to evaluate agile attributes that has important reference value for the airline companies in aviation industry.Practical implicationsThe findings of this study will support managers in the airline industry to conduct airline operations more flexibly and effectively to take sustainable competitive advantage in unexpected and dynamic environment.Originality/valueTo the author' best knowledge, this study is the first developed to identify the attributes necessary to increase agility in LCCs. Thus, as a systematic tool, a framework is developed for the implementation of agile attributes to achieve sustainable competitive advantage in the airline industry and presented a roadmap for airline managers to deal with crises and challenging situations by satisfying customer and increasing competitiveness.

New constraints on Triton’s atmosphere from the 6 October 2022 stellar occultation

The atmosphere of Triton was probed directly by observing a ground-based stellar occultation on 6 October 2022. This rare event yielded 23 positive light curves collected from 13 separate observation stations contributing to our campaign. The significance of this event lies in its potential to directly validate the modest pressure fluctuation on Triton, a phenomenon not definitively verified by previous observations, including only five stellar occultations, and the Voyager 2 radio occultation in 1989. Using an approach consistent with a comparable study, we precisely determined a surface pressure of 14.07−0.13+0.21 μbar in 2022. This new pressure rules out any significant monotonic variation in pressure between 2017 and 2022 through direct observations, as it is in alignment with the 2017 value. Additionally, both the pressures in 2017 and 2022 align with the 1989 value. This provides further support for the conclusion drawn from the previous volatile transport model simulation, which is consistent with the observed alignment between the pressures in 1989 and 2017; that is to say, the pressure fluctuation is modest. Moreover, this conclusion suggests the existence of a northern polar cap extended down to at least 45°N–60°N and the presence of nitrogen between 30°S and 0°.

Ices on pebbles in protoplanetary discs

ABSTRACT The formation of solid macroscopic grains (pebbles) in protoplanetary discs is the first step towards planet formation. We aim to study the distribution of pebbles and the chemical composition of their ice mantles in a young protoplanetary disc. We use the two-dimensional hydrodynamical code feosad in the thin-disc approximation, which is designed to model the global evolution of a self-gravitating viscous protoplanetary disc taking into account dust coagulation and fragmentation, thermal balance, and phase transitions and transport of the main volatiles (H2O, CO2, CH4, and CO), which can reside in the gas, on small dust ($\lt 1\, \mu\mathrm{ m}$), on grown dust ($\gt 1\, \mu\mathrm{ m}$) and on pebbles. We model the dynamics of the protoplanetary disc from the cloud collapse to the 500 kyr moment. We determine the spatial distribution of pebbles and composition of their ice mantles and estimate the mass of volatiles on pebbles, grown dust, and small dust. We show that pebbles form as early as 50 kyr after the disc formation and exist until the end of simulation (500 kyr), providing prerequisites for planet formation. All pebbles formed in the model are covered by icy mantles. Using a model considering accretion and desorption of volatiles on to dust/pebbles, we find that the ice mantles on pebbles consist mainly of H2O and CO2, and are carbon-depleted compared to gas and ices on small and grown dust, which contain more CO and CH4. This suggests a possible dominance of oxygen in the composition of planets formed from pebbles under these conditions.

Constraints on the evolution of the Triton atmosphere from occultations: 1989–2022

Context. In about 2000, the south pole of Triton experienced an extreme summer solstice that occurs every ∼650 years, when the subsolar latitude reached about 50°S. Bracketing this epoch, a few occultations probed the Triton atmosphere in 1989, 1995, 1997, 2008, and 2017. A recent ground-based stellar occultation observed on 6 October 2022 provides a new measurement of the atmospheric pressure on Triton. This is presented here. Aims. The goal is to constrain the volatile transport models (VTMs) of the Triton atmosphere. The atmosphere is basically in vapor pressure equilibrium with the nitrogen ice at its surface. Methods. Fits to the occultation light curves yield the atmospheric pressure of Triton at the reference radius 1400 km, from which the surface pressure is deduced. Results. The fits provide a pressure p1400 = 1.211 ± 0.039 μbar at radius 1400 km (47 km altitude), from which a surface pressure of psurf = 14.54 ± 0.47 μbar is deduced (1σ error bars). To within the error bars, this is identical to the pressure derived from the previous occultation of 5 October 2017, p1400 = 1.18 ± 0.03 μbar and psurf = 14.1 ± 0.4 μbar, respectively. Based on recent models of the volatile cycles of Triton, the overall evolution of the surface pressure over the last 30 years is consistent with N2 condensation taking place in the northern hemisphere. However, models typically predict a steady decrease in the surface pressure for the period 2005-2060, which is not confirmed by this observation. Complex surface-atmosphere interactions, such as ice albedo runaway and formation of local N2 frosts in the equatorial regions of Triton, could explain the relatively constant pressure between 2017 and 2022.

Volatiles Detection in Lunar Polar Region

In lunar science, volatiles are defined as chemical elements and unstable compounds, evaporating, sublimating, or flowing in other ways at low temperature. At moderate temperature, volatiles transfers its flowing elements from solid materials to coexisting gas phases. Such substances include S, Cu, Zn, As, Se, Ag, Cd, In, Te, Hg, Ti, Pb, Bi, and halogens (F, C L, Br, and I). These volatile substances are mainly added by small impactors, so they should be uniformly deposited in lunar regolith. In the permanently shaded regions (PSRs) of the lunar polar region, the extremely low temperature may allow the solar activity record to be kept longer. When the lunar soil is heated, it will release volatile elements in the form of gas, especially the particles injected into the lunar soil by the solar wind. In deeper lunar soil, it means that these particles were implanted in different periods of solar evolution. The study of regolith in polar PSRs may help to solve this problem, because it has not been widely heated and therefore may not be subjected to postimplantation modification. The research on volatiles detection in lunar polar region can help us confirm the content and distribution of water ice in the permanent shadow region of the lunar polar region, and the composition, distribution, source, transport and loss mechanism of other volatiles in this region, as well as the relationship between lunar soil in the polar region and the ancient solar wind environment, and the environment and mineral resources in the region. Chandrayaan-3 provided important assistance to the conceptualization of this project. At the end of the article, we discussed the lunar orbit.

Stellar Occultations with the 3.6-m DOT: Probing Planetary Atmospheres

The present paper (which is based on Sicardy et al. (2021)) discusses investigation of solar system bodies made possible by the simple yet powerful technique of stellar occultation. We focus on the stellar occultation by Pluto on 2020 June 6. The event was observed at Devasthal, Nainital, India in the I and H bands with the 1.3-m and 3.6-m telescopes, respectively. From the observed light curve, the surface pressure of Pluto’s atmosphere was constrained to psurf = 12.23−0.38+0.65 μbar. This indicates a continuing plateau phase since mid-2015 which is in excellent agreement with the prediction of Pluto volatile transport model of Meza et al. (2019). This result stresses the importance of coordinated stellar occultation observations with facilities like Devasthal Optical Telescope (DOT) and Himalayan Chandra Telescope (HCT) where a few minutes of observing time lead to high-impact science.

Reconciling results of 2019 and 2020 stellar occultations on Pluto’s atmosphere

A stellar occultation by Pluto on 5 September 2019 yielded positive detections at two separate stations. Using an approach consistent with comparable studies, we derived a surface pressure of 11.478 ± 0.55 µbar for Pluto’s atmosphere from the observations of this event. In addition, to avoid potential method inconsistencies when comparing with historical pressure measurements, we reanalyzed the data for the 15 August 2018 and 17 July 2019 events. All the new measurements provide a bridge between the two different perspectives on the pressure variation since 2015: a rapid pressure drop from previous studies of the 15 August 2018 and 17 July 2019 events and a plateau phase from that of the 6 June 2020 event. The pressure measurement from the 5 September 2019 event aligns with those from 2016, 2018, and 2020, supporting the latter perspective. While the measurements from the 4 June 2011 and 17 July 2019 events suggest probable V-shaped pressure variations that are unaccounted for by the volatile transport model (VTM), the VTM remains applicable on average. Furthermore, the validity of the V-shaped variations is debatable given the stellar faintness of the 4 June 2011 event and the grazing single-chord geometry of the 17 July 2019 event. To reveal and understand all of the significant pressure variations of Pluto’s atmosphere, it is essential to provide constraints on both the short-term and long-term evolution of the interacting atmosphere and surface by continuous pressure monitoring through occultation observations whenever possible, and to complement these with frequent spectroscopy and photometry of the surface.

Stomatal closure prevents xylem transport of green leaf volatiles and impairs their systemic function in plants.

Plants perceive environmental stresses as whole organisms via distant signals conveying danger messages through their vasculature. In parallel to vascular transport, airborne plant volatile compounds, including green leaf volatiles (GLVs), can bypass the lack of vascular connection. However, some small volatile compounds move through the vasculature; such vascular transport is little known about GLVs. Here we illustrate GLV alcohols as solutes move within xylem vessels in Zea mays. We describe GLV alcohols, including Z-3-hexen-ol and its isomer E-3-hexen-ol, which is not synthesized in maize, moving through the transpiration stream via xylem vessels. Since transpiration is mediated by the stomatal aperture, closing stomata by two independent methods diminishes the transport of GLV alcohol and its isomer. In addition, the lower transport of GLV alcohols impairs their function in inducing terpenoid biosynthesis, suggesting that xylem transport of GLV alcohols plays a significant role in their systemic function. Our study suggests that GLV alcohols, in addition to airborne signals, are transported through xylem vessels. Our findings can be critical in future studies about the perception and function of these compounds in plants.

Molecular analysis of NlugCSP3 with behaviorally active ligands of the brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae)

The insect olfactory system is sensitive to the complicated chemical environment. Insect’s chemosensory proteins (CSPs) supposedly act as transport of plant volatiles across the sensillar lymph and competitive fluorescent binding assay was commonly used to test the binding affinities with various plant volatiles. However, extensive research to determine the physiological role of CSPs is necessary and helpful through binding interaction of a protein with the plant volatiles. In this comparative study, we employed phylogenetic analysis, fluorescence spectra, quenching mode, and thermodynamic force to characterize Nilaparvata lugens CSP3 (NlugCSP3). The phylogenetic tree revealed that amino acid sequence of NlugCSP3 showed extremely close similarities with Laodelphax striatella (LstrCSP10 & LstrCSP11) and Sogatella furcifera (SurCSP3). The Stern-Volmer (SV) curve of NlugCSP3 fluorescence quenching indicated that nonadecane and 2-tridecanone clearly quenched NlugCSP3 fluorescence as a stable static quenching mode. Meanwhile, α-terpinene and farnesene collided with NlugCSP3, instead of forming stable complexes. The thermodynamic analysis of NlugCSP3 revealed that spontaneous binding interaction occurred in nonadecane and 2-tridecanone and is driven primarily by hydrophobic interactions. This study not only provides the information about the binding interaction of protein with the volatiles, but also improves the efficient recognition of behaviorally elicited volatiles that could be used in the management of brown planthopper.

Bolometric Hemispherical Albedo Map of Pluto from New Horizons Observations

The New Horizons encounter with the Pluto system revealed Pluto to have an extremely spatially variable surface with expansive dark, bright, and intermediate terrains, refractory and volatile ices, and ongoing/recent endogenous and exogenous processes. Albedo is useful for understanding volatile transport because it quantifies absorbed solar energy; albedo may also provide insights into surface processes. Four filters of the New Horizons LORRI and MVIC imagers are used to approximate the bolometric (flux-weighted, wavelength-integrated) albedo. The bolometric hemispherical albedo (local energy balance albedo) as a function of the incidence angle of the solar illumination is measured for both Cthulhu and Sputnik Planitia, which are extensive, extreme dark and extreme bright terrains on Pluto. For both terrains, the bolometric hemispherical albedo increases by >30% from 0° to 90° incidence. The incidence-angle-average bolometric hemispherical albedo of Cthulhu is 0.12 ± 0.01, and that of Sputnik Planitia is 0.80 ± 0.06, where uncertainties are estimates based on scatter from different photometric functional approximations. The bolometric Bond albedo (global energy balance albedo) of Cthulhu is 0.12 ± 0.01, and that of Sputnik Planitia is 0.80 ± 0.07. A map of Pluto’s incidence-angle-average bolometric hemispherical albedo is produced. The incidence-angle-average bolometric hemispherical albedo, spatially averaged over areas north of ≈30° S, is ≈0.54. Pluto has three general albedo categories: (1) very low albedo southern equatorial terrains, including Cthulhu; (2) high-albedo terrains, which constitute most of Pluto’s surface; and (3) very high albedo terrains, including Sputnik Planitia. Pluto’s extraordinary albedo variability with location is also spatially sharp at some places.

Thermal Environments and Volatile Stability Within Lunar Pits and Caves

AbstractLunar collapse pits and possible caves have been suggested as ideal locations for the storage and protection of lunar water ice deposits, due to their potential to create permanently shadowed regions (PSRs) at high latitudes and ability to protect ice from destructive surface processes. However, the thermal environments of these features have not been investigated at high latitudes, and it remains unclear what effects pit latitude and geometry would have on interior temperatures and ice stability. We create a 3D thermal and volatile transport model and use it to characterize the thermal environments and volatile‐trapping potential within lunar collapse pits and caves. We model the thermal behavior of lunar pits as it varies with latitude for several different pit geometries. We then apply the thermal model results to the volatile transport model and calculate water loss rates to space given an initial ice deposit. The model shows that in general, high‐latitude pits make poor cold traps for ice because their enclosed geometry increases the ability of multiple‐scattered infrared radiation to elevate pit interior temperatures. Although, the enclosed geometry of a cave might help trap volatiles in theory, in practice ice stability within pits and caves is primarily controlled by temperature and not geometric effects. We find that ice loss rates are higher within pits and caves than within PSRs of craters at similar latitudes. Nevertheless, some specific situations arise where pits can act as effective cold traps, such as when pits lie within PSRs created by exterior topography.

Metamorphism and Deformation on Subduction Interfaces: 2. Petrological and Tectonic Implications

AbstractThe compositional range of ∼2,000 marine sediments and ∼19,000 oceanic igneous rocks is encapsulated by a set of 12 sedimentary and 10 mafic rock compositions, allowing computation of phase relationships on P‐T paths along subduction interfaces. These are described economically by a partitioning analysis, which connects the mineral assemblages to different parts of the subduction P‐T space and facilitates assessment of prograde dehydration, melting, densification, and rheological systematics. Dehydration and densification occur at shallower depths than in studies that neglect shear heating. Lawsonite stability is limited to interfaces where convergence is slower than 20 mm/yr; such rates also favor transport of volatiles beyond the arc. Terrigenous sediments and mafic rocks reach their solidi close to the top of the wedge‐slab interface; melt fractions are enhanced by fluid from the dehydrating slab interior. Rheological calculations show that the most abundant sediment types have interface capacities of hundreds of meters to kilometers, and that the strengths of mafic rocks comfortably exceed their buoyancy stresses. Above ∼650°C sediments are weak enough to rise as diapirs into the mantle wedge. Carbonate‐ and serpentinite‐rich lithologies are weaker than other interface rocks, and ascend most rapidly at the cessation of subduction. Ascent rates drop abruptly as rocks enter the plate interface, probably leading to retrograde equilibrium at P ∼ 1–1.5 GPa. The seismic‐aseismic transition is expected at about 500°C in mafics, and 400°C in metasediments. Seamounts are weaker than most other interface rocks, and unlikely to form asperities. Slow slip and tremor may be associated with the blueschist‐eclogite transition.

Pluto’s Surface Mapping Using Unsupervised Learning from Near-infrared Observations of LEISA/Ralph

We map the surface of Pluto using an unsupervised machine-learning technique using the near-infrared observations of the LEISA/Ralph instrument on board NASA’s New Horizons spacecraft. The principal-component-reduced Gaussian mixture model was implemented to investigate the geographic distribution of the surface units across the dwarf planet. We also present the likelihood of each surface unit at the image pixel level. Average I/F spectra of each unit were analyzed—in terms of the position and strengths of absorption bands of abundant volatiles such as N2, CH4, and CO and nonvolatile H2O—to connect the unit to surface composition, geology, and geographic location. The distribution of surface units shows a latitudinal pattern with distinct surface compositions of volatiles—consistent with the existing literature. However, previous mapping efforts were based primarily on compositional analysis using spectral indices (indicators) or implementation of complex radiative transfer models, which need (prior) expert knowledge, label data, or optical constants of representative end-members. We prove that an application of unsupervised learning in this instance renders a satisfactory result in mapping the spatial distribution of ice compositions without any prior information or label data. Thus, such an application is specifically advantageous for a planetary surface mapping when label data are poorly constrained or completely unknown, because an understanding of surface material distribution is vital for volatile transport modeling at the planetary scale. We emphasize that the unsupervised learning used in this study has wide applicability and can be expanded to other planetary bodies of the solar system for mapping surface material distribution.