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Ice chemistry in the dense, cold interstellar medium (ISM) is probably responsible for the formation of interstellar complex organic molecules (COMs). Recent laboratory experiments performed at T ∼ 4 K have shown that irradiation of CO:N2 ice samples analog to the CO-rich interstellar ice layer can contribute to the formation of COMs when H2 molecules are present. We have tested this organic chemistry under a broader range of conditions relevant to the interior of dense clouds by irradiating CO:15N2:H2 ice samples with 2 keV electrons in the 4–15 K temperature range. The H2 ice abundance depended on both, the ice formation temperature and the thermal evolution of the samples. Formation of H-bearing organics such as formaldehyde (H2CO), ketene (C2H2O), and isocyanic acid (H15NCO) was observed upon irradiation of ice samples formed at temperatures up to 10 K, and also in ices formed at 6 K and subsequently warmed up and irradiated at temperatures up to 15 K. These results suggest that a fraction of the H2 molecules in dense cloud interiors might be entrapped in the CO-rich layer of interstellar ice mantles, and that energetic processing of this layer could entail an additional contribution to the formation of COMs in the coldest regions of the ISM. [ABSTRACT FROM AUTHOR]

Multispectral mapping data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) provide a unique opportunity to characterize south polar ice deposits at higher spectral sampling, spatial resolution, or spatiotemporal coverage than previous work. This new perspective can help constrain the nature and distribution of different mixtures of CO2 ice, H2O ice, and dust that influence the formation, evolution, and preservation of Mars climate records. We processed 1,103 CRISM observations spanning the southern summer of six Mars Years (MYs) through a combination of k‐means clustering and random forest classification. Using a set of 12 spectral endmembers directly tied to previous work with high‐resolution CRISM targeted data, we made a series of temporally restricted mosaics showing surface spectral variation over time. The mosaics show the effects of the MY 28 dust storm on the removal of the seasonal CO2 ice cap that year and reveal how this process differed from the years that followed. A mosaic showing residual ice surfaces displays broad agreement with previous compositional maps while resolving new details in the distribution of H2O ice‐rich material around the periphery of the bright CO2 ice cap. By showing how surface composition varies across a broad swath of the south polar region through time, the endmember set and classified mosaics produced in this work can provide critical context for future studies of the dynamic processes that shape south polar ice deposits. Plain Language Summary: At the south pole of Mars, different mixtures of CO2 ice, water ice, and dust on the surface influence interactions with the atmosphere. These influences affect how polar ice deposits are formed, how they change over time, and how they are preserved as records of past climates. Existing maps of ice and dust in the region have limitations in how accurately they can describe mixtures and how much detail they can show on the ground. Using data from an orbiting spectrometer that measures sunlight reflected from the surface, we made new maps that reveal important details not seen in previous work. For example, these maps show how surface composition changes through time, which can be used to study CO2 frost that forms on the surface every winter and is removed in the summer. We observe how a dust storm in 1 year affected the composition and/or thickness of seasonal frost compared with other years. The maps also reveal how composition varies in different permanent ice deposits. Compared to previous work, it is easier to see how CO2 ice and dust are mixed with water ice in enigmatic exposures that may be linked to the formation of new climate records. Key Points: Variable mixtures of CO2 and H2O ice with dust are linked to the formation of south polar climate recordsTo better understand these mixtures, we mapped 12 endmembers across multispectral data spanning 6 south polar summersWe made a series of mosaics to explore compositional variation in both seasonal and residual ice deposits [ABSTRACT FROM AUTHOR]

We present a semi-analytic model for the growth, drift, desorption, and fragmentation of millimeter- to meter-sized particles in protoplanetary disks. Fragmentation occurs where particle collision velocities exceed critical fragmentation velocities. Using this criterion, we produce fragmentation regions in disk orbital radius–particle size phase space for particles with a range of material properties, structures, and compositions (including SiO _2 , Mg _2 SiO _4 , H _2 O, CO _2 , and CO). For reasonable disk conditions, compact aggregate H _2 O, CO _2 , and CO ice particles do not reach destructive relative velocities and are thus not likely to undergo collisional fragmentation. Uncoated silicate particles are more susceptible to collisional destruction and are expected to fragment in the inner disk, consistent with previous work. We then calculate the growth, drift, and sublimation of small particles, initially located in the outer disk. We find that ice-coated particles can avoid fragmentation as they grow and drift inward under a substantial range of disk conditions, as long as the particles are aggregates composed of 0.1 μ m-sized monomers. Such particles may undergo runaway growth in disk regions abundant in H _2 O or CO _2 ice, depending on the assumed disk temperature structure. These results indicate that icy collisional growth to planetesimally relevant sizes may happen efficiently throughout a disk’s lifetime, and is particularly robust at early times when the disk’s dust-to-gas ratio is comparable to that of the interstellar medium.

Laboratory-derived optical constants are essential for identifying ices and measuring their relative abundances on solar system objects. Almost all optical constants of ices important to planetary science come from experiments with transmission geometries. Here we describe our new experimental setup and the modification of an iterative algorithm in the literature to measure the optical constants of ices from experiments with reflectance geometries. We apply our techniques to CH _4 ice and H _2 O ice samples and find good agreement between our values and those in the literature, except for one CH _4 band in the literature that likely suffers from saturation. The work we present here demonstrates that labs with reflectance geometries can generate optical constants essential for the proper analysis of near- and mid-infrared spectra of outer solar system objects such as those obtained with the James Webb Space Telescope.

Current maps of compositional variation across south polar ice exposures on Mars do not resolve the meter‐scales at which erosional processes are most active, ultimately limiting our understanding of how the deposits form and evolve and how they can be used to interpret long‐term climate records. In this study, we use k‐means clustering and random forest classification to identify and map a set of universal spectral endmembers across 167 high‐resolution observations acquired during southern summer by the Compact Reconnaissance Imaging Spectrometer for Mars. The 21 endmembers show distinct combinations and strengths of key infrared absorption features reflecting diverse mixtures of CO2 ice, H2O ice, and dust. The resulting compositional framework can be used to characterize the nature of both seasonal CO2 frost and the residual ices it overlies across a variety of terrains. Following the large dust event of Mars Year 28, the residual CO2‐ice deposits (RCD) were covered by an unusually thick or long‐lived deposit of seasonal frost. Within the RCD, low‐albedo material around erosional features display H2O ice absorptions consistent with exposures around the outer margins of the RCD. These peripheral water‐ice deposits show unexpected variation in CO2 ice and dust content. Most notably, regions within several km of the edge of the RCD display spectral contributions from CO2 ice even after seasonal frost has been removed. These results can inform investigations focused on the dynamics of seasonal CO2 deposition, the development of erosional morphologies, and the creation of climate records in south polar stratigraphy. Plain Language Summary: Ice deposits near the south pole of Mars contain varied mixtures of CO2 ice, water ice, and dust. These mixtures influence interactions with solar heating and atmospheric cycling that affect the formation, evolution, and preservation of different ice deposits. However, ice composition in this region has not been mapped in sufficient detail to fully understand these dynamic processes. We used high‐resolution data gathered from an orbiting spectrometer that measured sunlight reflected from the surface. Through automated and manual techniques, we identified the most typical reflectance signatures in the data set and generated maps showing where those materials are located. These results reveal unprecedented detail in the nature of both seasonal (removed during summer) and residual (remaining on the surface throughout each year) ice deposits. The most compelling findings are that (a) increased seasonal CO2 ice thickness or retention appeared following a large dust storm, (b) residual CO2 ice is found to extend beyond the brightest deposits, and (c) water ice‐rich exposures reveal more varied CO2 ice and dust content than previously understood. The compositional framework provided by the study can help guide future investigations into a variety of processes that shape south polar ices and the climate records they preserve. Key Points: One hundred sixty‐seven south polar observations by the Compact Reconnaissance Imaging Spectrometer for Mars images were mapped with a set of 21 spectral endmembers representing a range of CO2 ice, H2O ice, and dust mixturesSeasonal CO2 ice cover was thicker or more prolonged in Mars Year 28, linking dust storms to cold‐trapping of CO2 on the bright residual iceCO2 ice signatures extend beyond the bright residual ice and into surrounding material, even in late summer after seasonal frost removal [ABSTRACT FROM AUTHOR]

Rock fragments of the Cb-type asteroid Ryugu returned to Earth by the JAXA Hayabusa2 mission share mineralogical, chemical, and isotopic properties with the Ivuna-type (CI) carbonaceous chondrites. Similar to CI chondrites, these fragments underwent extensive aqueous alteration and consist predominantly of hydrous minerals likely formed in the presence of liquid water on the Ryugu parent asteroid. Here we present an in situ analytical survey performed by secondary ion mass spectrometry from which we have estimated the D/H ratio of Ryugu’s hydrous minerals, D/H _Ryugu , to be [165 ± 19] × 10 ^−6 , which corresponds to δ D _Ryugu = +59 ± 121‰ (2 σ ). The hydrous mineral D/H _Ryugu ’s values for the two sampling sites on Ryugu are similar; they are also similar to the estimated D/H ratio of hydrous minerals in the CI chondrites Orgueil and Alais. This result reinforces a link between Ryugu and CI chondrites and an inference that Ryugu’s samples, which avoided terrestrial contamination, are our best proxy to estimate the composition of water at the origin of hydrous minerals in CI-like material. Based on this data and recent literature studies, the contribution of CI chondrites to the hydrogen of Earth’s surficial reservoirs is evaluated to be ∼3%. We conclude that the water responsible for the alteration of Ryugu’s rocks was derived from water ice precursors inherited from the interstellar medium; the ice partially re-equilibrated its hydrogen with the nebular H _2 before being accreted on the Ryugu’s parent asteroid.

The surface environmental conditions of many of the icy ocean worlds in the Solar System are outside of the thermal stability field of methane ice. However, mechanisms may exist that entrain or trap methane within water ice that arrives at the surface via plume eruptions or resurfacing events. At the surface, the ice grains may experience charged particle irradiation that could lead to the production of new complex hydrocarbons. We investigated the irradiation products of 12CH 4 versus 13CH 4 , the temperature dependence of CH 4 radiation processing and product stability, and the temperature stability of CH 4 when mixed with H 2 O in a cryogenic vacuum environment. Significantly, methane ice experimentally encased in water ice was irradiated at 100 K in an ultra-high vacuum environment and produced similar radiation-formed secondary phases as pure methane ice irradiated at 20 K. The methane radiation products produced outside of the methane ice thermal stability field, while encased in a water ice film, were most notably 13CO 2 and a candidate hydrocarbon feature. Evidence for complex hydrocarbons, such as C 2 H 6 , was observed during warming and sublimation of the sample. • The radiolysis of CH 4 ices at ocean world environmental conditions was investigated. • CH 4 ice inside H 2 O ice irradiated at 100 K created similar secondary phases as CH 4 ice. • The temperature dependence of CH 4 and CH 4 +H 2 O radiation processing was investigated. [ABSTRACT FROM AUTHOR]

We report JWST NIRCam observations of G0.253+0.016, the molecular cloud in the Central Molecular Zone known as “The Brick,” with the F182M, F187N, F212N, F410M, F405N, and F466N filters. We catalog 56,146 stars detected in all six filters using the crowdsource package. Stars within and behind The Brick exhibit prodigious absorption in the F466N filter that is produced by a combination of CO ice and gas. In support of this conclusion, and as a general resource, we present models of CO gas and ice and CO _2 ice in the F466N, F470N, and F410M filters. Both CO gas and ice contribute to the observed stellar colors. We show, however, that CO gas does not absorb the Pf β and Hu ϵ lines in F466N, but that these lines show excess absorption, indicating that CO ice is present and contributes to observed F466N absorption. The most strongly absorbed stars in F466N are extincted by ∼2 mag, corresponding to >80% flux loss. This high observed absorption requires very high column densities of CO, and thus a total CO column that is in tension with standard CO abundance and/or gas-to-dust ratios. This result suggests the CO/H _2 ratio and dust-to-gas ratio are greater in the Galactic Center than in the Galactic disk. Ice and/or gas absorption is observed even in the cloud outskirts, implying that additional caution is needed when interpreting stellar photometry in filters that overlap with ice bands throughout galactic centers.

The release of volatiles from comets is usually from direct sublimation of ices on the nucleus, but for very or hyperactive comets other sources have to be considered to account for the total production rates. In this work, we present new near-IR (NIR) imaging and spectroscopic observations of 46P/Wirtanen taken during its close approach to Earth on 2018 December 19 with the MMIRS instrument at the MMT Observatory to search for signatures of icy or ice-rich grains in its inner coma that might explain its previously reported excess water production. The morphology of the images does not suggest any change in grain properties within the field of view, and the NIR spectra do not show the characteristic absorption features of water ice. Using a new Markov Chain Monte Carlo–based implementation of the spectral modeling approach of Protopapa et al., we estimate the areal water ice fraction of the coma to be

JWST has shown that CO _2 and CO are common on the surfaces of objects in the Kuiper Belt and have apparent surface coverages even higher than that of water ice, though water ice is expected to be significantly more abundant in the bulk composition. Using full Mie scattering theory, we show that the high abundance and the unusual spectral behavior around the 4.26 μ m ν _1 band of CO _2 can be explained by a surface covered in a few micron thick layer of ∼1–2 μ m CO _2 particles. CO is unstable at the temperatures in the Kuiper Belt, so the CO must be trapped in some more stable species. While hydrate clathrates or amorphous water ice are often invoked as a trapping mechanism for outer solar system ices, the expected spectral shift of the absorption line for a CO hydrate clathrates or trapping in amorphous ice is not seen, nor does the H _2 O abundance appear to be high enough to explain the depth of the CO absorption line. Instead, we suggest that the CO is created via irradiation of CO _2 and trapped in the CO _2 grains during this process. The presence of a thin surface layer of CO _2 with embedded CO suggests volatile differentiation driving CO _2 from the interior as a major process driving the surface appearance of these mid-sized Kuiper Belt objects, but the mechanisms that control the small grain size and depth of the surface layer remain unclear.

The flexure of the lithosphere under stresses imposed by the geologically young south polar cap is one of the few clues we have regarding the south polar cap composition and the present‐day thermal state of Mars. Here, we combine radar, gravity, and topography data with a flexural loading model to estimate the bulk density (ρ) and average real dielectric constant (ε′) of the south polar cap, and the elastic thickness of the lithosphere (Te). Given the uncertainties of the data, our results constrain ρ to be 1,100–1,300 kg m−3 (best fit of 1,220 kg m−3), ε′ to be 2.5–3.4 (best fit of 3.3), and Te to be greater than 150 km (best fit of 360 km). Based on these results, the maximum lithospheric flexure is 770 m, and the polar cap volume could be up to 26% larger than previous estimates that did not account for lithospheric flexure. Our inferred compositions imply that the dust concentration would be at least 9 vol% if the CO2 ice content were negligible, and that the CO2 ice concentration would be more than the known 1 vol% CO2 if the dust concentration were less than 9 vol%. The 1‐σ lower limit on Te implies a surface heat flow that is less than 23.5 mW m−2. This lower limit is significantly less than the range of acceptable values at the north pole (330–450 km, heat flow of 11–16 mW m−2), and helps satisfy global thermal evolution simulations that predict hemispheric differences in surface heat flow. Plain Language Summary: The south polar cap of Mars is a tremendous reservoir of ices. It is transparent to radar wavelengths allowing us to probe its structure and composition. Here, we combine radar, gravity, and topography data with a flexural loading model to invert for the south polar cap composition and elastic thickness of the underlying lithosphere. We find that the lithosphere below the south pole is cold and strong, but with a rigidity that is potentially lower than at the north pole. The allowed range of lithospheric rigidities for the northern and southern lithospheres is compatible with hemispheric differences in heat flow of the planet predicted by thermal evolution models. The polar cap volume could be up to 26% higher than previous estimates that did not account for lithospheric flexure, which represents a significant quantity of trapped volatiles. Such as for the north pole, the south polar deposits are made mostly of water ice, and may have sequestered more CO2 ice than has currently been detected depending on the assumed dust content. An independent estimate on the dust content would allow placing crucial constraints on the amount of CO2 trapped in the south polar deposits. Key Points: Radar and gravity data are used to invert for the south polar cap composition and elastic thickness of the underlying lithosphere (Te)Te lower than at the north pole are allowed, which helps satisfy thermal evolution models that predict hemispheric heat flow patternsThe polar cap is made mostly of H2O and has more than the known 1 vol% CO2 if the dust concentration is less than 9 vol% [ABSTRACT FROM AUTHOR]

The geodynamical response of the lithosphere under stresses imposed by the geologically young north polar cap is one of the few clues we have to constrain both the polar cap composition and the present‐day thermal state of Mars. Here we combine radar data with a flexural loading model to self‐consistently estimate the density (ρ) and real dielectric constant (ε′) of the polar cap, and the elastic thickness of the lithosphere underneath (Te). Our results show that ρ ranges from 920 to 1,520 kg m −3, ε′ is 2.75 (+0.40, −0.35), and Te is between 330 and 450 km. We determine a polar cap volume that is up to 30% larger than current estimates that all neglect lithospheric flexure. Our inferred compositions suggest that, for dust content larger than about 6 vol%, 10 vol% CO 2 ice is mixed within the polar deposits, which has important implications for the climate evolution of Mars. Plain Language Summary: The north polar cap of Mars is a tremendous reservoir of ices and dust of unknown concentration and composition. It is transparent to radar giving us a unique insight into its structure and composition. Here we use a novel technique that combines radar and elevation data along with a flexure model, to invert for the polar cap composition and the strength of the underlying lithosphere. Similar to previous studies, we find that the lithosphere below the north pole is extremely rigid and does not deform much under the load of the polar cap. This implies that the north polar region is currently colder than the rest of the planet, which has profound implications for our understanding of the structure and evolution of the Martian interior. Our inferred compositions suggest that for reasonable dust contents, about 10 vol% CO 2 ice is mixed within the polar deposits. This is the first time a large quantity of CO 2 ice is constrained to exist in the north polar cap. Like on Earth, where the composition of buried ices gives hints on the climatic evolution, having CO 2 ice at the north pole of Mars will help improve scenarios for the climate evolution of the planet. Key Points: Radar data and a flexural loading model are used to probe the composition of the north polar cap of Mars and the strength of the lithosphereThe elastic thickness beneath the north polar cap is found to be between 330 and 450 km, implying regional heat flows of 11 to 16 mW m −2For reasonable dust contents, large quantities of CO 2 ice must be mixed within the polar cap to be consistent with our inferred compositions [ABSTRACT FROM AUTHOR]

Numerous investigations have measured and identified properties of water and exotic ices. These properties are measured at various pressures and temperatures; however, these disparate studies are sometimes difficult to find, confusing, or even contradictory. Here, we amass and present a catalogue of some temperature dependent equations on ice density, latent heat of fusion, constant values for latent heat of sublimation, specific heat capacity at constant pressure, thermal conductivity, and Arrhenius flow law parameters for water ice, carbon dioxide ice, and solid nitrogen. The equations are either directly cited from the sources or are fitted from data in past publications. [ABSTRACT FROM AUTHOR]

The surface of Europa is heavily irradiated by high-energy particles with the energy ranges of 1–100 MeV for primary electrons and ∼10 keV for secondary electrons. These irradiations may cause oxidation of surface materials, such as chlorides and sulfur-bearing species, through reactions with oxidative radicals formed by dissociation of H 2 O ice. Similar irradiation-induced oxidation could have occurred in near-surface ice on Mars. However, most of previous experiments simulated ∼10 keV electron irradiation onto ice materials on Europa and Mars, and few studies have investigated the oxidation of chlorides and sulfur by MeV electron irradiation. Here we performed laboratory experiments on MeV electron irradiation, as well as 10 keV electron and UV irradiations, onto mixtures of H 2 O ice and chlorides, or elemental sulfur, at low temperatures. Our experimental results indicate selective oxidation of sulfur against chlorides, with negligible formation of oxychlorides on irradiation of H 2 O ice and chloride mixtures, regardless of experimental conditions (temperature, electron energy, or presence of oxidants in ice). Sulfate is effectively formed by the electron irradiation. This selective oxidation may be caused by the different stabilities of atoms within irradiated H 2 O ice. If sulfate on Europa's surface is transported into the subsurface ocean, this could provide energy sources for possible chemoautotrophic life in the ocean. On Europa, sulfur would be one of key elements in redox chemistry on the surface and possibly in the subsurface ocean. • Laboratory experiments on irradiation-induced oxidation on planetary surface. • MeV and 10 keV electron irradiation onto mixtures of H 2 O ice and chlorides or sulfur. • Selective oxidation of sulfur against chlorides, with negligible formation of oxychlorides. • Sulfur would be one of key elements in redox chemistry on Europa. [ABSTRACT FROM AUTHOR]

Subglacial processes influence the large-scale behaviour of glaciers and determine the geological processes that occur at the ice-substrate interface. In this paper we focus on subglacial deformation beneath a cold-based glacier resting on permafrost. We ask what are the drivers of subglacial permafrost deformation, how is strain distributed beneath glaciers with a permafrost substrate, how is strain transmitted from the glacier into the substrate, and how is deformed permafrost incorporated into the basal zone of the glacier? To address these questions a tunnel excavated in the margin of Wright Lower Glacier in the McMurdo Dry Valleys, Antarctica to observe the structure of the basal zone and bed of the glacier and to monitor basal ice deformation over a period of 4 years. The tunnel revealed a stacked sequence of stratified debris-bearing and clean ice layers, and thick rafts of frozen sediment. Isotopic and gas analyses reveal that despite the low local temperature of the basal ice (−18.5 °C), liquid water has played an important role in the formation of this basal sequence. The rafts of frozen sediment contain well preserved sedimentary structures and algae layers that show the material has been entrained from the underlying permafrost. Deformation measurements made with a combination of displacement transducers, strain arrays, and plumb-lines show that strain and motion within the basal zone are heterogeneous and that strain is transmitted through the permafrozen sediment and into intra-sediment ice layers. The distribution of strain in the basal zone produces a compound velocity profile resembling the deformation patterns inferred from deformation structures in Pleistocene permafrost and also resembles profiles associated with subglacial sediment deformation driven by hydrogeological processes. We conclude that ice-rich permafrost is readily deformed by glaciers and that there is no clear boundary between basal ice and deforming permafrost. [ABSTRACT FROM AUTHOR]

We present here the first comprehensive study of the chemical composition of accretion ice from Lake Vostok. Ion chromatographic analyses were performed on samples obtained along the deeper part of the Vostok ice core. Samples were taken from 3350 down to 3611 m depth, both in glacier ice and subglacial lake ice. The total ionic contents of two accretion ice layers—a few meters thick and centered around 3540 and 3590 m depth—are several times lower than those of glacier ice. Very low concentrations were also observed in the deeper part of accretion ice, below 3609 m depth. Elsewhere, the total ionic content is variable but remains 5 to 50 times higher than in glacier ice. Whatever its total ionic content, the ionic composition of accretion ice is significantly different from what is observed in glacier ice. It is dominated by sodium chloride, homogeneously distributed throughout the ice lattice, as well as calcium and magnesium sulfate, likely located in solid inclusions, or to a lesser extent at grain boundaries. Chemical considerations combined with additional studies of sulfur and oxygen isotopes in sulfate, and iron measurements strongly suggest that glacier water recycling and bedrock hydrolysis do not play a prominent role in providing impurities to accretion ice. It is more likely that NaCl rich water carrying fine sulfate salt particles is sporadically incorporated in the ice accreting in a shallow bay upstream from Vostok. The origin of such salty water, which should also contribute to Lake salinity, is discussed. [Copyright &y& Elsevier]

Interpretation of new ice core data and reappraisal of existing data, both from the basal part of the Vostok ice core, give strong support to a kind of thermohaline circulation in Lake Vostok. Although the salinity of the lake is considered as weak (less than 1‰), the prominent influence of salinity at high pressure and low temperature on water density makes such a circulation possible. As a consequence, subglacial melting along the northern shores of the lake is balanced, further south, by frazil ice production in the upper water column, its accretion and consolidation at the ice–water interface followed by accreted ice export out of the system together with the southeasterly glacier flow. The dynamics of the system is documented by a stable water isotope budget estimate, by inferences concerning accreted ice formation and by an investigation of ice properties at the transition between meteoric ice and accreted ice. This complex behaviour is the controlling factor on water, biota and sediment fluxes in the lake environment. [Copyright &y& Elsevier]