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Jupiter's atmospheric water abundance is a highly important cosmochemical parameter that is linked to processes of planetary formation, weather, and circulation. Remote sensing and in situ measurement attempts still leave room for substantial improvements to our knowledge of Jupiter's atmospheric water abundance. With the motivation to advance our understanding of water in Jupiter's atmosphere, we investigate observations and models of deep clouds. We discuss deep clouds in isolated convective storms (including a unique storm site in the North Equatorial Belt that episodically erupted in 2021–2022), cyclonic vortices, and northern high-latitude regions, as seen in Hubble Space Telescope visible/near-infrared imaging data. We evaluate the imaging data in continuum and weak methane band (727 nm) filters by comparison with radiative transfer simulations, 5 micron imaging (Gemini), and 5 micron spectroscopy (Keck), and conclude that the weak methane band imaging approach mostly detects variation in the upper cloud and haze opacity, although sensitivity to deeper cloud layers can be exploited if upper cloud/haze opacity can be separately constrained. The cloud-base water abundance is a function of cloud-base temperature, which must be estimated by extrapolating 0.5-bar observed temperatures downward to the condensation region near 5 bar. For a given cloud base pressure, the largest source of uncertainty on the local water abundance comes from the temperature gradient used for the extrapolation. We conclude that spatially resolved spectra to determine cloud heights—collected simultaneously with spatially-resolved mid-infrared spectra to determine 500-mbar temperatures and with improved lapse rate estimates—would be needed to answer the following very challenging question: Can observations of deep water clouds on Jupiter be used to constrain the atmospheric water abundance? [ABSTRACT FROM AUTHOR]

This study is devoted to the estimation of dissociation rates for polycyclic aromatic hydrocarbons (PAHs) molecules due to ultraviolet photon absorption. Four methods are used for calculations. Specifically, the rates of dehydrogenation and destruction of the PAH carbon skeleton are calculated. The results obtained by different methods are compared. It is shown that the results differ significantly, and it is impossible unambiguously estimate minimum sizes and the degree of PAH hydrogenation. The results indicate the need to refine the theoretical models of PAH photodissociation and expand the experimental basis of PAH dissociative properties. [ABSTRACT FROM AUTHOR]

Mesospheric CO 2 clouds are one of two types of carbon dioxide clouds known on Mars. We present observations of mesospheric CO 2 clouds made by Atmospheric Chemistry Suite (ACS) onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter (TGO). We analyzed 1663 solar occultation sessions of Thermal InfraRed (TIRVIM) and Middle InfraRed (MIR) channels of ACS covering more than two Martian years that contain spectra of 2.7 μm carbon dioxide ice absorption band. That allowed us to unambiguously discriminate carbon dioxide ice aerosols from mineral dust and water ice aerosols, not relying on the information of atmospheric thermal conditions. CO 2 clouds were detected in eleven solar occultation observations at altitudes from 39 km to 90 km. In five cases, there were two or three layers of CO 2 clouds that were vertically separated by 5–15 km gaps. Effective radius of CO 2 aerosol particles is in the range of 0.1–2.2 μm. Spectra produced by the smallest particles indicate a need for a better resolved CO 2 ice refractive index. Nadir optical depth of CO 2 clouds is in the range 5 × 10−4–4 × 10−2 at both 2.7 μm and 0.8 μm. Asymmetrical diurnal distribution of detections observed by ACS is potentially due to local time variations of temperature induced by thermal tides. Two out of five cases of carbon dioxide cloud detections made by the TIRVIM instrument reveal the simultaneous presence of CO 2 ice and H 2 O ice aerosols. Temperature profiles measured by the Near InfraRed (NIR) channel of ACS are used to calculate CO 2 saturation ratio S at locations of carbon dioxide clouds. Supersaturation S > 1 is detected in only 6 out of 19 cases of CO 2 cloud layers; extremely low values of S < 0.1 are found in 9 out of 19 cases. • Detection of CO 2 mesospheric clouds relies on observing the 2.7 μm absorption band. • CO 2 clouds were detected in 11 solar occultation observations at 39–90 km altitudes. • Effective radius of CO 2 aerosol particles is in range of 0.1–2.2 μm. • Two cloud layers were formed by CO 2 and H 2 O ice aerosols. • CO 2 cloud layers with S > 1 detected in 6/19 cases, S < 0.1 found in 9/19 cases. [ABSTRACT FROM AUTHOR]

We have analyzed the 2-μm spectro-images of the polar haze of Jupiter, which were observed by the JIRAM/Juno between 2016 and 2021, to study the vertical and latitudinal distributions of the polar haze and its absorption and scattering properties. We construct 2-μm brightness maps of the polar haze by selecting specific spectral ranges where the haze spectral features are revealed. The constructed haze images show no distinctive structure above the 55oN/S latitudes showing fairly uniform and symmetrical distribution around the poles. We find no traces of the recently discovered stratospheric polar jets seen at radio wavelengths (Cavalié et al., 2021), of the circumpolar waves seen in the UV and around 8900 Å (e.g., Vincent et al., 2000; Barrado-Izagirre et al., 2008), nor of the mid-IR hot/bright spots on these images. These non-detections indicate that the major polar haze layers are lower than the jets and the mid-IR bright spots, but possibly higher than the circumpolar waves, and the thermal radiation from the mid-IR hot spots is negligible at 2 μm. We construct synthetic spectra between 2.0 and 2.5 μm, compare them with the JIRAM polar spectra, and find that the 2-μm polar haze is mostly located between 3 and 40 mbar pressure levels, approximately consistent with the previous results of Kim et al. (1991b), and also the literature values. We attempt to derive the anisotropic scattering properties of the haze particles for scattering angles between 60o and 120o, which is the only available range. The derived anisotropy tends to be moderate, but we are unable to determine a definite anisotropy within the statistical error bars of the observed data. We also derive the haze optical depths and single scattering albedos between 2.0 and 2.5 μm. The derived spectral structure of the opacity is roughly similar to those of hydrocarbon and nitrile ices of Titan retrieved by Sim et al. (2013) suggesting similar chemical compositions and possibly similar formation scenarios for Jupiter's haze particles but excluding nitrile ices. • We study the vertical and latitudinal distributions of the polar haze. • We construct 2-μm brightness maps of the polar haze. • We find that the 2-μm polar haze is mostly located between 3 and 40 mbar pressure levels. • Derived anisotropic scattering properties of the haze tend to be moderate. • Derived spectra of the haze are similar to those of Titan suggesting similar formation scenario. [ABSTRACT FROM AUTHOR]

Limb sounding of thermal emission in the infrared wavelength range is a powerful technique for measuring temperature and aerosols in the martian atmosphere. However, the long optical path may provide challenges to limb retrievals in high aerosol conditions. These can be mitigated by considering limb measurements in the far infrared, where opacities of most aerosols are lower than in the mid-infrared. We present analyses of radiative properties of Mars dust and water ice aerosols at far infrared wavelengths based on measurements by the Mars Climate Sounder (MCS) in limb geometry at mid- and far infrared wavelengths. For dust aerosols, derived far infrared radiative properties show a homogeneous behavior that is consistent with particle sizes in the order of 1 μm effective radius. Far infrared radiative properties for water ice aerosols exhibit a larger variability in local time and region, leading to significant differences between the aphelion cloud belt and the north polar hood, with the resulting parameters suggesting particle sizes around 3 μm or larger. Using the derived parameters, we develop a method for retrieving aerosol profiles from MCS limb measurements that combines information from mid- and far infrared spectroscopic channels. The use of far infrared channels enables aerosol profile retrievals from limb measurements that typically reach about a scale height deeper into the atmosphere than would be possible using mid-infrared channels only. The extended vertical range of the aerosol profiles allows the derivation of aerosol column optical depths through vertical integration, with dust column derivations in global or large-scale regional dust storms also being available by extrapolating dust profiles below the lowest retrievable altitude of a limb measurement. The quantification of aerosol columns allows us to retrieve surface brightness temperatures from MCS on-planet viewing measurements that are corrected for atmospheric contributions. We show that differences between surface brightness and top-of-the-atmosphere temperatures are typically within 20 K, with surface brightness temperatures generally being warmer (colder) than top-of-the-atmosphere temperatures at daytime (nighttime), except at high latitudes. [Display omitted] • We derive radiative properties of Mars dust and water ice in the far infrared from Mars Climate Sounder limb measurements. • Use of combined mid- and far infrared measurements enables aerosol profile retrievals of extended vertical range. • The extended vertical range of aerosol profiles allows the derivation of aerosol columns through vertical integration. [ABSTRACT FROM AUTHOR]

As tracers of the major volatile cycles of MarsCO 2 , H 2 O, and dustclouds are important for understanding the circulation of the martian atmosphere and hence martian climate. We present the spatial and seasonal distribution of laterally-confined clouds in the middle atmosphere of Mars during one Mars Year as identified in limb radiance measurements by the Mars Climate Sounder. Cloud identifications were made by citizen scientists through the "Cloudspotting on Mars" citizen science project, hosted on the citizen science platform Zooniverse. A method to aggregate the crowdsourced data using a novel clustering algorithm is developed. The derived cloud catalog is presented and the seasonal and spatial distribution of clouds is discussed in terms of key populations. • The Mars Climate Sounder serendipitously observes aerosol layers in limb observations. • The Cloudspotting on Mars citizen science project enabled identification of clouds throughout Mars Year 29. • A customized clustering algorithm optimizes the aggregation of citizen-scientist annotations. • Maps of clouds show effects of thermal tides and dust on cloud formation. [ABSTRACT FROM AUTHOR]

Rovibrational spectral data for several tetra-atomic silicon carbide clusters (TASCCs) are computed in this work using a CCSD(T)-F12b/cc-pCVTZ-F12 quartic force field. Accurate theoretical spectroscopic data may facilitate the observation of TASCCs in the interstellar medium which may lead to a more complete understanding of how the smallest silicon carbide (SiC) solids are formed. Such processes are essential for understanding SiC dust grain formation. Due to SiC dust prevalence in the interstellar medium, this may also shed light on subsequent planetary formation. Rhomboidal Si2C2 is shown here to have a notably intense (247 km mol−1) anharmonic vibrational frequency at 988.1 cm−1 (10.1 μm) for ν2, falling into one of the spectral emission features typically associated with unknown infrared bands of various astronomical regions. Notable intensities are also present for several of the computed anharmonic vibrational frequencies including the cyclic forms of C4, SiC3, Si3C, and Si4. These features in the 6–10 μm range are natural targets for infrared observation with the James Webb Space Telescope (JWST)’s MIRI instrument. Additionally, t-Si2C2, d-Si3C, and r-SiC3 each possess dipole moments of greater than 2.0 D making them interesting targets for radioastronomical searches especially since d-SiC3 is already known in astrophysical media.

The boreal hemisphere has been experiencing increasing extreme hot and dry conditions over the past few decades, consistent with anthropogenic climate change. The continental extension of this phenomenon calls for tools and techniques capable of monitoring the global to regional scales. In this context, satellite data can satisfy the need for global coverage. The main objective we have addressed in the present paper is the capability of infrared satellite observations to monitor the vegetation stress due to increasing drought and heatwaves in summer. We have designed and implemented a new water deficit index (wdi) that exploits satellite observations in the infrared to retrieve humidity, air temperature, and surface temperature simultaneously. These three parameters are combined to provide the water deficit index. The index has been developed based on the Infrared Atmospheric Sounder Interferometer or IASI, which covers the infrared spectral range 645 to 2760 cm−1 with a sampling of 0.25 cm−1. The index has been used to study the 2017 heatwave, which hit continental Europe from May to October. In particular, we have examined southern Italy, where Mediterranean forests suffer from climate change. We have computed the index's time series and show that it can be used to indicate the atmospheric background conditions associated with meteorological drought. We have also found a good agreement with soil moisture, which suggests that the persistence of an anomalously high water deficit index was an essential driver of the rapid development and evolution of the exceptionally severe 2017 droughts. [ABSTRACT FROM AUTHOR]

Between 2001 and 2023, we obtained high spectral resolution mid-infrared observations of Io using the TEXES instrument at NASA's Infrared Telescope Facility. These observations were centered at 529.8 cm-1 (18.88 μ m) and include several SO 2 absorption lines. By modeling the shapes and strengths of these absorption lines, we are able to determine how Io's SO 2 atmospheric density varies over the 22-year time period, covering nearly two Jovian years. Previous analysis has shown that the density of Io's atmosphere on the anti-Jovian hemisphere exhibits clear seasonal temporal variability, which can be modeled as the sum of a seasonally-varying frost sublimation component and a constant component, assumed to be volcanic. The new data show that the seasonal pattern repeats during the second Jovian year, confirming the importance of sublimation support. The considerable longitudinal variability in Io's atmospheric density found in previous work is also stable over the second Jovian year with the SO 2 column density on the Jupiter-facing hemisphere being 5–8 times lower than the anti-Jovian hemisphere. For the first time, we detect seasonal variability on the Jupiter-facing hemisphere as well. This can also be modeled as a combination of sublimation and a small constant source. The lower atmospheric density on the Jupiter-facing hemisphere can plausibly be explained by the daily Jupiter eclipses, which decrease the surface temperature and therefore reduce the sublimation-driven component of the atmosphere, combined with a lower level of volcanic activity directly emitting SO 2 into the atmosphere. • Io's SO 2 atmospheric density varies seasonally according to heliocentric distance. • The atmosphere is supported by sublimation of surface SO 2 frost on both hemispheres. • The atmospheric density is consistently much lower on the Jupiter-facing hemisphere. • Eclipses and inhomogeneous volcanic emissions may drive the longitudinal variability. [ABSTRACT FROM AUTHOR]

We analyze data from the final two years of the Cassini mission to retrieve the distributions of methane (CH 4), ethane (C 2 H 6), acetylene (C 2 H 2), ethylene (C 2 H 4), and benzene (C 6 H 6) in Saturn's upper stratosphere and mesosphere from stellar occultations observed by the Ultraviolet Imaging Spectrograph (UVIS), spanning latitudes from pole to pole. These observations represent the first two-dimensional snapshot of the photochemical production region with latitude and depth for these five light hydrocarbons around the northern summer solstice. To support this analysis, we combine temperature-pressure profiles retrieved from the UVIS occultations and limb scans observed by the Cassini Composite Infrared Spectrometer (CIRS) with the CH 4 profiles to provide atmospheric structure models for each occultation location that span the middle and upper atmosphere. We detect a strong meridional trend in the homopause pressure level that implies much weaker mixing at the poles than near the subsolar point. This is shown by the homopause pressure level, which ranges from ∼ 0. 05 μ bar around the subsolar point to ∼ 5 μ bar at the poles, with the corresponding values of the eddy diffusion coefficient K z z ranging from ∼ 1000 m 2 s−1 to 1–10 m 2 s−1, respectively, at the 2 μ bar level. This trend could be explained by upwelling at low latitudes and downwelling at high latitudes in both hemispheres and we estimate that vertical wind speeds of less than 2 cm s−1 would be required. The distributions of the photochemical products follow the homopause trend but they also show a clear seasonal trend at pressures between 0.01 and 10 μ bar, with higher abundances in the summer hemisphere than in the winter hemisphere. We compare the observed distributions with results from one-dimensional seasonal photochemical models, with and without ion chemistry, to explore the impact of ion chemistry on the results. The best agreement between the models and the observations is obtained in the summer hemisphere, whereas disagreements in the winter hemisphere and auroral region may be due to the lack of transport by global circulation and auroral electron and ion precipitation in our photochemical models. Ion chemistry is particularly important for matching the observed C 6 H 6 distribution, whereas differences between the neutral only and ion chemistry models are more modest for the other species. We also compare the C 2 H 2 profiles retrieved from the UVIS occultations to those retrieved from the CIRS limb scans and find good agreement between the retrievals at pressures where they overlap. [Display omitted] • We present the distribution of hydrocarbons in Saturn's stratosphere with latitude and pressure. • Results from Cassini stellar occultations in the ultraviolet agree well with infrared limb scans. • The methane homopause is much deeper at the poles than at the equator. • The observed hydrocarbon distribution follows a seasonal trend, with important exceptions. [ABSTRACT FROM AUTHOR]

Jupiter’s atmospheric water abundance is a highly important cosmochemical parameter that is linked to processes of planetary formation, weather, and circulation. Remote sensing and in situ measurement attempts still leave room for substantial improvements to our knowledge of Jupiter’s atmospheric water abundance. With the motivation to advance our understanding of water in Jupiter’s atmosphere, we investigate observations and models of deep clouds. We discuss deep clouds in isolated convective storms (including a unique storm site in the North Equatorial Belt that episodically erupted in 2021–2022), cyclonic vortices, and northern high-latitude regions, as seen in Hubble Space Telescope visible/near-infrared imaging data. We evaluate the imaging data in continuum and weak methane band (727 nm) filters by comparison with radiative transfer simulations, 5 micron imaging (Gemini), and 5 micron spectroscopy (Keck), and conclude that the weak methane band imaging approach mostly detects variation in the upper cloud and haze opacity, although sensitivity to deeper cloud layers can be exploited if upper cloud/haze opacity can be separately constrained. The cloud-base water abundance is a function of cloud-base temperature, which must be estimated by extrapolating 0.5-bar observed temperatures downward to the condensation region near 5 bar. For a given cloud base pressure, the largest source of uncertainty on the local water abundance comes from the temperature gradient used for the extrapolation. We conclude that spatially resolved spectra to determine cloud heights—collected simultaneously with spatially-resolved mid-infrared spectra to determine 500-mbar temperatures and with improved lapse rate estimates—would be needed to answer the following very challenging question: Can observations of deep water clouds on Jupiter be used to constrain the atmospheric water abundance?

The ammonium ion (NH 4 +) has been suggested to be present in interstellar ices and has been observed on the surfaces of planetary bodies using infrared (IR) spectroscopy as the primary means of identification. Evidence for several ammonium salts has also been found in the dust and surface ices of comet 67P/Churyumov-Gerasimenko. Here we present a laboratory study of ammonium cyanide (NH 4 CN) and report on several properties of this compound, measured with higher accuracy than in previous reports, including its IR band strengths and optical constants for use in quantifying its abundance in interstellar and planetary ices. We also report the first measurements since 1882 of NH 4 CN vapor pressures, sublimation fluxes, and sublimation enthalpy measured at temperatures relevant to subliming cometary ices (134–155 K). The density and refractive index of NH 4 CN at 125 K and the sublimation enthalpy and vapor pressures of NH 3 at ~100 K are also reported. • Laboratory study of ammonium cyanide and ammonia. • Ammonium cyanide infrared spectra and band strengths at low temperatures. • Ammonium cyanide infrared optical constants, mass density and refractive index. • Sublimation pressure and enthalpy of sublimation for ammonium cyanide. • Vapor pressure and enthalpy of sublimation for ammonia. [ABSTRACT FROM AUTHOR]

Off-nadir measurements by the Mars Climate Sounder are an underutilized source of information about planetary-scale waves and their role in the climate. More than 8 Mars years of data is currently available. The data set is used here to investigate a pair of waves whose vertical structure is well aligned with the off-nadir contribution function of the A3 channel. Both waves have a zonal wavenumber of 1 and a large amplitude in the high-latitude, winter-season, westerly jet. One is an eastward-traveling free wave with a period of 15–20 sols; it recurs annually in the north, appearing in most years in a roughly 50-sol span that ends near the winter solstice. The other is a forced Rossby wave that alternates between the north and the south, emerging at the autumnal equinox and subsiding at the vernal equinox. It is stationary with respect to the surface in the south and quasi-stationary in the north. A-type and C-type regional dust storms cause a conspicuous increase in the amplitude of the northern forced wave through their effect on the meridional overturning circulation. The dust-storm enhancement of the overturning circulation is initially confined in longitude, as determined by the spatial distribution of dust in the southern hemisphere at the start of the storm. The amplification of the forced wave is a consequence of this zonal asymmetry. The wave amplitude increases rapidly at the start of each dust storm and returns to its pre-storm level 10–15 sols later when the distribution of dust becomes zonally uniform. A detailed description of the forced wave is obtained from the OpenMARS reanalysis, whose reliability is confirmed by comparisons with the off-nadir measurements. During the early stage of the A and C storms, the wave amplitude exceeds 3 km in geopotential height and the center of the polar vortex is displaced from the pole. In addition, the northern forced wave exhibits a pre-winter-solstice phase reversal whose origin is not known. • Properties of atmospheric waves are derived from 8 years of spacecraft observations. • Wave-1 stationary Rossby waves respond dramatically to forcing by large dust storms. • The wave forcing is a consequence of zonal asymmetry in the dust distribution. • Dust-storm forcing is the main source of year-to-year variability of the Rossby wave. • There is an unexplained pre-solstice phase reversal in the northern forced wave. [ABSTRACT FROM AUTHOR]

The depositional history of alluvial fans on Mars provides insight into the climatic conditions during the time of fan formation in the late Hesperian to early Amazonian. However, traditional stratigraphic analysis of the alluvial fan deposits is not possible across most of Mars. This study assesses the use of thermal inertia data as a tool for sedimentologic interpretation of 437 Mars alluvial fans. Based on previous work demonstrating the relationship between depositional style, grain size, and thermophysical properties, this study uses analysis of the thermal inertia of alluvial fan surfaces across the global population of fans on Mars to make an assessment of depositional styles that built the alluvial fans. The thermal inertia values across the global population of fans are indicative of sand- to pebble-sized sediment. The variability of grain sizes across the global population is more homogenous than expected based on comparisons to terrestrial alluvial fans. Nearly all Mars alluvial fans have an average thermal inertia that corresponds to pebble and smaller grain size, and < 1% of Mars alluvial fans have an average thermal inertia that corresponds to cobble-sized grains. Spatial patterns of thermal inertia variability on alluvial fan surfaces show a small number of fans with evidence for either downslope fining or channelization, but the majority of fans show no recognizable geologic patterns in surface thermal inertia. The interpretation of the thermal inertia-derived grain size suggests that either there is widespread mantling of unconsolidated sand across the surface, or that Mars alluvial fans were built by primarily sand-sized sediment, which may be indicative of lower energy sediment transport events. • Thermal inertia of alluvial fan surfaces indicates primarily sand-sized sediment. • Thermal inertia of Mars alluvial fan surfaces is surprisingly homogeneous globally. • Alluvial fans built by sand-sized sediment suggest low energy fluvial processes. • Fluvial depositional processes may correlate to lack of clay in catchments. [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]

The boreal hemisphere has been experiencing increasing extreme hot and dry conditions over the past few decades, consistent with anthropogenic climate change. The continental extension of this phenomenon calls for tools and techniques capable of monitoring the global to regional scales. In this context, satellite data can satisfy the need for global coverage. The main objective we have addressed in the present paper is the capability of infrared satellite observations to monitor the vegetation stress due to increasing drought and heatwaves in summer. We have designed and implemented a new water deficit index (wdi) that exploits satellite observations in the infrared to retrieve humidity, air temperature, and surface temperature simultaneously. These three parameters are combined to provide the water deficit index. The index has been developed based on the Infrared Atmospheric Sounder Interferometer or IASI, which covers the infrared spectral range 645 to 2760 cm−1 with a sampling of 0.25 cm−1. The index has been used to study the 2017 heatwave, which hit continental Europe from May to October. In particular, we have examined southern Italy, where Mediterranean forests suffer from climate change. We have computed the index’s time series and show that it can be used to indicate the atmospheric background conditions associated with meteorological drought. We have also found a good agreement with soil moisture, which suggests that the persistence of an anomalously high water deficit index was an essential driver of the rapid development and evolution of the exceptionally severe 2017 droughts.

Spectroscopic solar occultation measurements by the Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus/Solar Occultation at Infrared instrument (SPICAV/SOIR) onboard the Venus Express orbiter gave new data about upper haze aerosol properties, its vertical distribution and spatial and temporal variations. Early study with three channels of SPICAV/SOIR instrument using a few selected orbits indicated presence of two aerosol modes in particle size distribution (Wilquet et al., 2009). Analysis of aerosol properties from the SPICAV−IR spectrometer for the whole Venus Express data set obtained from May 2006 till November 2014 has proved it for some occultations (Luginin et al., 2016). In this work, we report retrieval of the upper haze (81–100 km) aerosol properties from 101 simultaneous SPICAV−UV and –IR solar occultation sessions acquired between March 2007 and January 2013. A joint analysis of the data from two spectrometers allowed us to characterize the size distribution ∼10 km higher in the atmosphere compared to previous analysis and to detect bimodal distribution in ∼50% of observations previously believed to be unimodal. At altitudes 81–92 km bimodality is observed in >50% of cases. Mode 2 particles are detected up to 98 km and mode 1 up to 100 km. Mean radius equals 0.14 ± 0.03 μm for mode 1 and 0.78 ± 0.18 μ m for mode 2. Number density profiles for both modes of particles exponentially decrease with altitude, starting from 50 cm−3 and 0.3 cm−3 at 82 km for mode 1 and mode 2, respectively, and reaching 3 cm−3 at 98 km for mode 1 and 0.03 cm−3 at 94 km for mode 2. • At altitudes 81–92 km bimodal distribution was observed in >50% of observations. • The mean effective radii are 0.14 ± 0.03 μm for mode 1 and 0.78 ± 0.18 μm for mode 2. • Number density profiles for both modes exponentially decrease with altitude. • Effective variance of mode 1 reaches 0.4 at <84 km and 0.03–0.15 at higher altitudes. • Effective variance of mode 2 is almost constant with height with mean value 0.04 ± 0.02. [ABSTRACT FROM AUTHOR]

We present a study of the long term variability of Jupiter's mid-infrared CH 4 auroral emissions. 7.7–7.9 μ m images of Jupiter recorded by NASA's Infrared Telescope Facility, Subaru and Gemini-South over the last three decades were collated in order to quantify the magnitude and timescales over which the northern auroral hotspot's CH 4 emission varies. These emissions predominantly sound the 10- to 1-mbar pressure range and therefore highlight the temporal variability of lower-stratospheric auroral-related heating. We find that the ratio of the radiance of the poleward northern auroral emissions to a lower-latitude zonal-mean, henceforth 'Relative Poleward Radiance' or RPR, exhibits variability over a 37% range and over a range of apparent timescales. We searched for patterns of variability in order to test whether seasonally varying solar insolation, the 11-year solar cycle, or short-term solar wind variability at Jupiter's magnetopause could explain the observed evolution. The variability of the RPR exhibits a weak (r < 0.2) correlation with both the instantaneous and phase-lagged solar insolation received at Jupiter's high-northern latitudes. This rules out the hypothesis suggested in previous work (e.g. Sinclair et al. 2017a, 2018) that shortwave solar heating of aurorally produced haze particles is the dominant auroral-related heating mechanism in the lower stratosphere. We also find the variability exhibits negligible (r < 0.18) correlation with both the instantaneous and phase-lagged monthly-mean sunspot number, which therefore rules out a long-term variability associated with the solar cycle. On shorter timescales, we find moderate correlations of the RPR with solar wind conditions at Jupiter in the preceding days before images were recorded. For example, we find correlations of r = 0.45 and r = 0.51 of the RPR with the mean and standard deviation solar wind dynamical pressure in the preceding 7 days. The moderate correlation suggests that either: (1) only a subset of solar wind compressions lead to brighter, poleward CH 4 emissions and/or (2) a subset of CH 4 emission brightening events are driven by internal magnetospheric processes (e.g. Io activity) and independent of solar wind enhancements. • Jupiter's 1-mbar auroral heating exhibits moderate correlations with solar wind variations. • Jupiter's 1-mbar auroral heating exhibits negligible correlations with the 11-year solar cycle. • Jupiter's 1-mbar auroral heating cannot result from shortwave solar heating of haze particles. [ABSTRACT FROM AUTHOR]

We present in this Keck AO paper the first global high angular resolution observations of Io in three broadband near-infrared filters: Kc (2.3 mu m), Lp (3.8 mu m), and Ms (4.7 mu m). The Keck AO observations are composed of 13 data sets taken during short time intervals spanning 10 nights in December, 2001. The MISTRAL deconvolution process, which is specifically aimed for planetary images, was applied to each image. The spatial resolution achieved with those ground-based observations is 150, 240, and 300 km in the Kc, Lp, and Ms band, respectively, making them similar in quality to most of the distant observations of the Galileo/NIMS instrument. Eleven images per filter were selected and stitched together after being deprojected to build a cylindrical map of the entire surface of the satellite. In Kc-band, surface albedc, features, such as paterae (R > 60 km) are easily identifiable. The Babbar region is characterized by extremely low albedo at 2.2 mu m, and shows an absorption band at 0.9 mu m in Galileo/SSI data. These suggest that this region is covered by dark silicate deposits, possibly made of orthopyroxene. In the Lp-Ms (3-5 mu m) bands, the thermal emission from active centers is easily identified. We detected 26 hot spots in both broadband filters over the entire surface of the minor planet; two have never been seen active before, nine more are seen in the Ms band. We focused our study on the hot spots detected in both broadband filters. Using the measurements of their brightness, we derived the temperature and area covered by 100 brightness measurements. Loki displayed a relatively quiescent activity. Dazhbog, a new eruption detected by Galileo/NIMS in August 2001, is a major feature in our survey. We also point out the fading of Tvashtar volcanic activity after more than two years of energetic activity, and the presence of a hot, but small, active center at the location of Surt, possibly a remnant of its exceptional eruption detected in February 2001. Two new active centers, labeled F and V on our data, are detected. Using the best temperature and the surface area derived from the L and M band intensities, we calculated the thermal output of each active center. The most energetic hot spots are Loki and Dazhbog, representing respectively 36 and 19% of the total output calculated from a temperature fit of all hot spots (20.6 x 10(12) W). Based on the temperature derived from hot spots (similar to 400 K), our measurement can unambiguously identify the contribution to the heat flux from the silicate portion of the surface. Because the entire surface was observed, no extrapolation was required to calculate that flux. It is also important to note that we measured the brightness of the individual hot spots when they were located close to the Central Meridian. This minimizes the line-of-sight effect which does not follow strictly a classical cosine law. Finally, we argue that despite the widespread volcanic activity detected, Io was relatively quiescent in December 2001, with a minimum mean total output of 0.4-1.2 W m(-2). This output is at least a factor of two lower than those inferred from observations made at longer wavelengths and at different epochs. (c) 2005 Elsevier Inc. All rights reserved.

Ganymede's surface exhibits great geological diversity, with old dark terrains, expressed through the surface composition, which is known to be dominated by two constituents: H 2 O-ice and an unidentified darkening agent. In this paper, new investigations of the composition of Ganymede's surface at global scale are presented. The analyses are derived from the linear spectral modeling of a high spectral resolution dataset, acquired with the near-infrared (1.40–2.50 μm) ground-based integral field spectrometer SINFONI (SIN gle F aint O bject N ear-IR I nvestigation) of the Very Large Telescope (VLT hereafter) located in Chile. We show that, unlike the neighboring moon Europa, photometric corrections cannot be performed using a simple Lambertian model. However, we find that the Oren-Nayar (1994) model, generalizing the Lambert's law for rough surfaces, produces excellent results. Spectral modeling confirms that Ganymede's surface composition is dominated by H 2 O-ice, which is predominantly crystalline, as well as a darkening agent, but it also clearly highlights the necessity of secondary species to better fit the measurements: sulfuric acid hydrate and salts, likely sulfates and chlorinated. A latitudinal gradient and a hemispherical dichotomy are the strongest spatial patterns observed for the darkening agent, the H 2 O-ice, and the sulfuric acid: the darkening agent is by far the major compound at the equator and mid-latitudes (≤ ± 35°N), especially on the trailing hemisphere, while the H 2 O-ice and the sulfuric acid are mostly located at high latitudes and on the leading hemisphere. This anti-correlation is likely a consequence of the bombardment of the constituents in the Jovian magnetosphere which are much more intense at latitudes higher than ±35°N. Furthermore, the modeling confirms that polar caps are enriched in small, fresh, H 2 O-ice grains (i.e. ≤50 μm) while equatorial regions are mostly composed of larger grains (i.e. ≥200 μm, up to 1 mm). Finally, the spatial distribution of the salts is neither related to the Jovian magnetospheric bombardment nor the craters. These species are mostly detected on bright grooved terrains surrounding darker areas. Endogenous processes, such as freezing of upwelling fluids going through the ice shell, may explain this distribution. In addition, a small spectral residue that might be related to brines and/or hydrated silica-bearing minerals are located in the same areas. • Near-infrared global mapping of Ganymede's surface from a ground-based telescope • Overall, an unidentified darkening agent is the major compound around the equator. • The water ice, mostly the crystalline form, is dominant at high latitudes (≥ ± 40°N). • Salts, very likely endogenic, improve spectral modeling for young geological regions. • A hemispherical dichotomy, due to Jupiter's magnetospheric bombardment, is observed. [ABSTRACT FROM AUTHOR]

During the years 2016 to 2018, the instruments Akatsuki/IR2 (JAXA) and IRTF/SpeX (NASA) acquired a large set of images at 1.74, 2.26 and 2.32 μm to study the nightside mid-to-lower clouds (48–60 km) of Venus. Here we summarize the rich variety of cloud morphologies apparent in these images: from frequent wave packets and billows caused by shear instabilities, to features reported decades ago like the circum-equatorial belts, bright blotches and equatorial troughs, and previously unseen features like dark spots, sharp dark streaks at mid latitudes and fully-developed vortices. • Summary of the main morphologies found on the nightside lower clouds of Venus. • The full dataset of images from Akatsuki/IR2 and images from IRTF/SpeX were explored. • New morphologies found: vortices, sharp dark streak and black spots. • The bright trough, blotch and the circum-equatorial belts seen again on Venus after decades. [ABSTRACT FROM AUTHOR]

• First detailed analysis of Pluto's H 2 O-ice rich sites. • Evidence for heavy hydrocarbons (i.e., C 3 H 8). • Test for CH 3 OH using new optical constants. On July 14, 2015, the New Horizons spacecraft made its closest approach to Pluto at about 12,000 km from its surface (Stern et al., 2015). Using the LEISA (Linear Etalon Imaging Spectral Array) near-IR imaging spectrometer we obtained two scans across the encounter hemisphere of Pluto at 6–7 km/pixel resolution. By correlating each spectrum with a crystalline H 2 O-ice model, we find several sites on Pluto's surface that exhibit the 1.5, 1.65 and 2.0 µm absorption bands characteristic of H 2 O-ice in the crystalline phase. These sites tend to be isolated and small (≲ 5000 km2 per site). We note a distinct near-IR blue slope over the LEISA wavelength range and asymmetries in the shape of the 2.0 µm H 2 O-ice band in spectra with weak CH 4 -ice bands and strong H 2 O-ice bands. These characteristics are indicative of fine-grain (grain diameters < wavelength or ∼ 1 µm) H 2 O-ice, like that seen in the spectra of Saturnian rings and satellites. However, the best-fit Hapke models require small mass fractions (≲10−3) of fine-grained H 2 O-ice that we can exchange for other refractory materials in the models with little change in χ 2, which may mean that the observed blue slope is possibly not due to a fine-grained material but an unidentified material with a similar spectral characteristic. We use these spectra to test for the presence of amorphous H 2 O-ice and estimate crystalline-to-amorphous H 2 O-ice fractions between 30 and 100%, depending on the location. We also see evidence for heavy hydrocarbons via strong absorption at λ > 2.3 µ m. Such heavy hydrocarbons are much less volatile than N 2 , CH 4 , and CO at Pluto temperatures. We test for CH 3 OH, C 2 H 6 , C 2 H 4 , and C 3 H 8 -ices because they have known optical constants and these ices are likely to arise from UV and energetic particle bombardment of the N 2 , CH 4 , CO-rich surface and atmosphere. Finally, we attempt to estimate the surface temperature using optical constants of pure CH 4 , and H 2 O-ice and best-fit Hapke models. Our standard model gives temperature estimates between 40 and 90 K, while our models including amorphous H 2 O-ice give lower temperature estimates between 30 and 65 K. [ABSTRACT FROM AUTHOR]

The research is an integrated effort beginning with telescopic observations and extending through detailed mineralogical characterizations to provide constraints on the albedo, diameter, composition, and meteorite affinity for the near-Earth asteroid 162385 (2000 BM19). Results of the analysis indicate a diameter ranging from 0.46 to 0.57 km (km) using albedo values of 0.20, 0.25, and 0.30. 2000 BM19 exhibits 1- and 2-μm absorption features from which a compositional analysis was conducted revealing Fs 23 and Fa 28 values, which are consistent with the Fa and Fs values for the LL-chondrites. • A mineralogical assessment of NEA 2000 BM19 was completed. • Constraints on albedo, diameter, composition, and meteorite affinity are reported. • 2000 BM19's Fs and Fa values are consistent with values for the LL-type OCs. [ABSTRACT FROM AUTHOR]

We present an analysis of Voyager-1-IRIS and Cassini-CIRS spectra of Jupiter's high latitudes acquired during the spacecrafts' respective flybys in November 1979 and January 2001. We performed a forward-model analysis in order to derive the abundances of ethylene (C 2 H 4), methylacetylene (CH 3 C 2 H), diacetylene (C 4 H 2) and benzene (C 6 H 6) in Jupiter's northern and southern auroral regions. We also compared these abundances to: 1) lower-latitude abundances predicted by the Moses et al. (2005) 'Model A' photochemical model, henceforth 'Moses 2005A', and 2) abundances derived at non-auroral longitudes in the same latitude band. This paper serves as an extension of Sinclair et al. (2017b) , where we retrieved the vertical profiles of temperature, C 2 H 2 and C 2 H 6 from similar datasets. We find that an enrichment of C 2 H 4 , CH 3 C 2 H and C 6 H 6 with respect to lower-latitude abundances is required to fit the spectra of Jupiter's northern and southern auroral regions. For example, for CIRS 0.5 cm−1 spectra of Jupiter's southern auroral region, scale factor enrichments of 6.40 −1.15 +1.30 and 9.60 −3.67 +3.98 are required with respect to the Moses 2005A vertical profiles of C 2 H 4 and C 6 H 6 , respectively, in order to fit the spectral emission features of these species at ∼950 and ∼674 cm−1. Similarly, in order to fit the CIRS 2.5 cm−1 spectra of Jupiter's northern auroral region, scale factor enrichments of 1.60 −0.21 +0.37, 3.40 −1.69 +1.89 and 15.00 −4.02 +4.01 with respect to the Moses 2005A vertical profiles of C 2 H 4 , CH 3 C 2 H and C 6 H 6 were required, respectively. Outside of Jupiter's auroral region in the same latitude bands, only upper-limit abundances of C 2 H 4 , CH 3 C 2 H and C 6 H 6 could be determined due to the limited sensitivity of the measurements, the weaker emission features combined with cooler stratospheric temperatures (and therefore decreased thermal emission) of these regions. Nevertheless, for a subset of the observations, derived abundances of C 2 H 4 and C 6 H 6 in Jupiter's auroral regions were higher (by 1 σ) with respect to upper-limit abundances derived outside the auroral region in the same latitude band. This is suggestive that the influx of energetic ions and electrons from the Jovian magnetosphere and external solar-wind environment into the neutral atmosphere in Jupiter's auroral regions drives enhanced ion-related chemistry, as has also been inferred from Cassini observations of Saturn's high latitudes (Fletcher et al., 2018 ; Guerlet et al., 2015 ; Koskinen et al., 2016). We were not able to constrain the abundance of C 4 H 2 in either Jupiter's auroral regions or non-auroral regions due to its lower (predicted) abundance and weaker emission feature. Thus, only upper-limit abundances were derived in both locations. From CIRS 2.5 cm−1 spectra, the upper limit abundance of C 4 H 2 corresponds to a scale factor enhancement of 45.6 and 23.8 with respect to the Moses 2005A vertical profile in Jupiter's non-auroral and auroral regions. • Ethylene, methylacetylene and benzene are enriched in Jupiter's auroral regions. • Enriched abundances suggest ion-related chemistry driven by auroral precipitation. • Ion-related chemistry also inferred from Cassini observations of Saturn's poles. • Negligible constraint on diacetylene's abundance due to its weaker line feature. [ABSTRACT FROM AUTHOR]

Abstract We present a new method for the determination of the surface properties of airless bodies from measurements of the emitted infrared flux. Our approach uses machine learning techniques to train, validate, and test a neural network representation of the thermophysical behavior of the atmosphereless body given shape model, illumination and observational geometry of the remote sensors. The networks are trained on a dataset of thermal simulations of the emitted infrared flux for different values of surface rock abundance, roughness, and values of the thermal inertia of the regolith and of the rock components. These surrogate models are then employed to retrieve the surface thermal properties by Markov Chain Monte Carlo Bayesian inversion of observed infrared fluxes. We apply the method to the inversion of simulated infrared fluxes of asteroid (101195) Bennu – according to a geometry of observations similar to those planned for NASA's OSIRIS-REx mission – and infrared observations of asteroid (25143) Itokawa. In both cases, the surface properties of the asteroid – such as surface roughness, thermal inertia of the regolith and rock component, and relative rock abundance – are retrieved; the contribution from the regolith and rock components are well separated. For the case of Itokawa, we retrieve a rock abundance of about 85% for pebbles larger than the diurnal skin depth, which is about 2 cm. The thermal inertia of the rock is found to be lower than the expected value for LL chondrites, indicating that the rocks on Itokawa could be fractured. The average thermal inertia of the surface is around 750 J s−1/2 K−1 m−2 and the measurement of thermal inertia of the regolith corresponds to an average regolith particle diameter of about 10 mm, consistently with in situ measurements as well as results from previous studies. Highlights • Thermophysical simulations can be streamlined in neural-network response functions. • Neural nets can quickly predict infrared fluxes from surface properties of asteroids. • Bayesian inference using neural nets allow retrieving rock abundance of the surface. • Inversion of fluxes of (25143) Itokawa gives results consistent with previous works. [ABSTRACT FROM AUTHOR]

Highlights • We used Cassini data to infer the composition of Titan's impact craters. • In RADAR radiometry data, degraded craters have higher emissivity than fresh ones. • In VIMS spectral data, craters in the dunes regions differ from those in the plains. • We suggest there are active surface processes occurring on Titan, like wind or rain. • These processes clear off its surface, while filling subsurface cracks with organics. Abstract Titan, the only moon in the solar system with a considerable atmosphere, is host to a variety of exogenic processes that shape its surface. These processes form features that are quite similar to features on Earth, including sand dunes, rivers, and lakes. The combination of a thick atmosphere and active surface processes also leads to a scarcity of impact craters on the surface of Titan. The compositions of these craters vary and may relate to the type and extent of erosion occurring at their location. In this work, we examined the composition of 12 impact features on Titan using Cassini's Visible and Infrared Mapping Spectrometer (VIMS) and 2.18 cm emissivity data from the RADAR radiometer on board the probe. Comparisons were made between crater composition as inferred from VIMS and composition as inferred from emissivity data with corresponding crater characteristics such as latitude, longitude and erosional state. We see a correlation between crater subsurface composition as inferred from the emissivity data and its erosional state and location. Well-preserved craters typically are more enriched in water-ice than degraded, organic-rich craters, suggesting that variations in composition are partially controlled by erosion and infilling. Moreover, craters located in dune fields show more subsurface organic enrichment than craters within the plains, which indicates that the efficiency of erosion and infilling varies with location and geologic context. VIMS data provide complementary information about crater surficial composition. We note that VIMS spectra do not change with erosional state, but rather appear to depend on the crater location on the moon. We suggest that there are active surface processes occurring on Titan, such as wind or rain, which are actively clearing off its surface and filling in subsurface fractures with organic materials. These processes would act to change the emissivity of the craters over time but leave the surface sensed by VIMS unchanged. [ABSTRACT FROM AUTHOR]

Highlights • Using spectral indices, average olivine abundance is (60 ± 15)%. • Olivine is homogeneous on Itokawa's surface, apart from a reduction in Sagamihara. • Spectral indices may be used as first guess for synthetic spectra. • Using synthetic spectra, average olivine abundance is (60 ± 7.5)%. • Itokawa belongs to S asteroid complex and is a potential source of LL chondrites. Abstract Olivine is one of the main abundant mineral in the Solar System, and the determination of its abundance on a surface may give fundamental information about its evolution. The study of surface distribution of olivine on asteroid (25143) Itokawa through near-Infrared reflectance spectroscopy is a difficult goal because olivine and pyroxene bands centred at 1 μm and 2 μm are not entirely included in Hayabusa/NIRS' spectral range. In this work, the retrieval of olivine abundance has been performed by applying two different methods: the first one uses some spectral indices to retrieve olivine abundance, whilst the second one consists of the application of the Hapke's theory in order to create synthetic spectra aimed at fitting a selection of NIRS' spectra. The analysis performed with the first method brought to an approximately homogeneous distribution of olivine content (60 ± 15% on average) on Itokawa's surface, with the exception of Sagamihara region, which has a slightly (up to 10%) lower olivine content. The second method brought to an average 60 ± 7.5% olivine content within 5 selected spectra, with the same reduction found in the spectrum from the Sagamihara region. All these values are in agreement with literature values on this topic, especially with the ones retrieved from particles sampled in Muses Sea by the Hayabusa probe. [ABSTRACT FROM AUTHOR]

Highlights • We present an analysis of the complete Visual Infrared Mapping Spectrometer (VIMS) data archive of Titan acquired by the Cassini mission. • We have computed a collection of multispectral summary products which are made available online at vims.univ-nantes.fr. • We describe empirical correction steps to produce seamless global mosaics of Titan in several wavelengths. • A global map of band ratios reveals the main spectral heterogeneities of Titan's surface. Abstract We have analyzed the complete Visual and Infrared Mapping Spectrometer (VIMS) data archive of Titan. Our objective is to build global surface cartographic products, by combining all the data gathered during the 127 targeted flybys of Titan into synthetic global maps interpolated on a grid at 32 pixels per degree (∼1.4 km/pixel at the equator), in seven infrared spectral atmospheric windows. Multispectral summary images have been computed for each single VIMS cube in order to rapidly identify their scientific content and assess their quality. These summary images are made available to the community on a public website (vims.univ-nantes.fr). The global mapping work faced several challenges due to the strong absorbing and scattering effects of the atmosphere coupled to the changing observing conditions linked to the orbital tour of the Cassini mission. We determined a surface photometric function which accounts for variations in incidence, emergence and phase angles, and which is able to mitigate brightness variations linked to the viewing geometry of the flybys. The atmospheric contribution has been reduced using the subtraction of the methane absorption band wings, considered as proxies for atmospheric haze scattering. We present a new global three color composite map of band ratios (red: 1.59/1.27 µm; green: 2.03/1.27 µm; blue: 1.27/1.08 µm), which has also been empirically corrected from an airmass (the solar photon path length through the atmosphere) dependence. This map provides a detailed global color view of Titan's surface partially corrected from the atmosphere and gives a global insight of the spectral variability, with the equatorial dunes fields appearing in brownish tones, and several occurrences of bluish tones localized in areas such as Sinlap, Menvra and Selk craters. This kind of spectral map can serve as a basis for further regional studies and comparisons with radiative transfer outputs, such as surface albedos, and other additional data sets acquired by the Cassini Radar (RADAR) and Imaging Science Subsystem (ISS) instruments. [ABSTRACT FROM AUTHOR]

Highlights • The most prominent surface feature in quadrangle Ac-H-6 is crater Haulani. • Negative visual to near-infrared spectral slopes are observed in crater Haulani'ejecta and in other small unnamed craters. • Mg- and NH 4 -phyllosilicates are depleted in crater Haulani's floor and bright ejecta. • Mg- and NH 4 -bearing mineral phases correlate only in Haulani crater's area. • Ca- and Na-carbonates are most abundant in bright material found in crater Haulani. Abstract Ac-H-6 'Haulani' is one of five quadrangles that cover the equatorial region of the dwarf planet Ceres. This quadrangle is notable for the broad, spectrally distinct ejecta that originate from the crater Haulani, which gives the name to the quadrangle. These ejecta exhibit one of the most negative ('bluest') visible to near infrared spectral slope observed across the entire body and have distinct color properties as seen in multispectral composite images. Besides Haulani, here we investigate a broader area that includes other surface features of interest, with an emphasis on mineralogy as inferred from data obtained by Dawn's Visible InfraRed mapping spectrometer (VIR), combined with multispectral image products from the Dawn Framing Camera (FC) so as to enable a clear correlation with specific geologic features. Our analysis shows that crater Haulani stands out compared to other surface features of the quadrangle. Albedo maps obtained in the near infrared range at 1.2 µm and 1.9 µm reveal that the floor and ejecta of Haulani are indeed a patchwork of bright and dark material units. Visible to near-infrared spectral slopes display negative values in crater Haulani's floor and ejecta, highlighting bluish, younger terrains. Diagnostic spectral features centered at ∼2.7 µm and ∼3.1 µm respectively indicate a substantial decrease in the abundances of magnesium-bearing phyllosilicates and ammoniated phyllosilicates in crater Haulani's floor and bright ejecta. Similar, but less prominent, spectral behavior is observed in other geologic features of this quadrangle, while the general trend in quadrangle Ac-H-6 for these two mineral species is to increase from the northwest to the southeast. However, it is worth noting that the correlation between the ∼2.7 µm and ∼3.1 µm spectral parameters is generally strong in the Haulani crater's area, but much weaker elsewhere, which indicates a variable degree of mixing between these two major mineral phases in moving away from the crater. Finally, the region of crater Haulani displays a distinct thermal signature and a local enhancement in calcium and possibly sodium carbonate minerals, which is hardly found in the rest of the quadrangle and is likely the result of intense hydrothermal processes following the impact event. These evidences all together confirm the young age of crater Haulani, as they have not been erased or made elusive by space weathering processes. [ABSTRACT FROM AUTHOR]

Highlights • High-resolution spectra of emission from hot SO gas on Io are presented. • Models with SO gas reservoirs at both high and low temperatures are preferred. • Spectra from different dates suggest atmospheric cooling during eclipse. • Models indicate a change in gas density of only ∼ 50% during eclipse. • The SO emission appears uncorrelated with volcanic activity or Io's orbit. Abstract Jupiter's moon Io hosts a dynamic atmosphere that is continually stripped off and replenished through frost sublimation and volcanic outgassing. We observed an emission band at 1.707 µm thought to be produced by hot SO molecules directly ejected from a volcanic vent; the observations were made with the NIRSPEC instrument on the Keck II telescope while Io was in eclipse by Jupiter on three nights in 2012–2016, and included two observations with 10 × higher spectral resolution than all prior observations of this band. These high-resolution spectra permit more complex and realistic modeling, and reveal a contribution to the SO emission from gas reservoirs at both high and low rotational temperatures. The scenario preferred by de Pater et al. (2002) for the source of the SO gas – direct volcanic emission of SO in the excited state – is consistent with these two temperature components if the local gas density is high enough that rotational energy can be lost collisionally before the excited electronic state spontaneously decays. Under this scenario, the required bulk atmospheric gas density and surface pressure are n ∼ 1011 cm − 3 and 1–3 nbar, consistent with observations and modeling of Io's dayside atmosphere at altitudes below 10 km (Lellouch et al., 2007; Walker et al., 2010). These densities and pressures would be too high for the nightside density if the atmospheric density drops by an order of magnitude or more at night (as predicted by sublimation-supported models), but recent results have shown a drop in SO 2 gas density of only a factor of 5 ± 2 (Tsang et al., 2016). While our observations taken immediately post-ingress and pre-egress (on different dates) prefer models with only a factor of 1.5 change in gas density, a factor of 5 change is still well within uncertainties. In addition, our derived gas densities are for the total bulk atmosphere, while Tsang et al. (2016) specifically measured SO 2. The low-temperature gas component is warmer for observations in the first 20 min of eclipse (in Dec 2015) than after Io had been in shadow for 1.5 h (in May 2016), suggesting cooling of the atmosphere during eclipse. However, individual spectra during the first ∼ 30 min of eclipse do not show a systematic cooling, indicating that such a cooling would have to take place on a longer timescale than the ∼ 10 min for cooling of the surface (Tsang et al., 2016). Excess emission is consistently observed at 1.69 µm, which cannot be matched by two-temperature gas models but can be matched by models that over-populate high rotational states. However, a detailed assessment of disequilibrium conditions will require high-resolution spectra that cover both the center of the band and the wing at 1.69 µm. Finally, a comparison of the total band strengths observed across eight dates from 1999 to 2016 reveals no significant dependence on thermal hot spot activity (including Loki Patera), on the time since Io has been in shadow, nor on the phase of Io's orbit at the time of observation. [ABSTRACT FROM AUTHOR]

In this paper, I present how near and mid-infrared observations can be used for the study of planetary nebulae and related objects. I present the main observing techniques, from the ground and space, highlighting main differences and how they can be complementary. I also highlight some new observing facilities and present the infrared observatories of the future to show that the future of infrared observations of planetary nebulae is bright.

Highlights • First spectral analysis of Nix, Hydra and Kerberos. • Crystalline water ice found on all three. • 2.21 µm band seen on Nix and Hydra indicating an ammoniated species. • Disk resolved spectroscopy of Nix. • Temperature and crystalline H2O-ice fraction estimated for Nix and Hydra. Abstract On July 14, 2015, NASA’s New Horizons spacecraft encountered the Pluto-system. Using the near-infrared spectral imager, New Horizons obtained the first spectra of Nix, Hydra, and Kerberos and detected the 1.5 and 2.0 µm bands of H 2 O-ice on all three satellites. On Nix and Hydra, New Horizons also detected bands at 1.65 and 2.21 µm that indicate crystalline H 2 O-ice and an ammoniated species, respectively. A similar band linked to NH 3 -hydrate has been detected on Charon previously. However, we do not detect the 1.99 µm band of NH 3 -hydrate. We consider NH 4 Cl (ammonium chloride), NH 4 NO 3 (ammonium nitrate) and (NH 4) 2 CO 3 (ammonium carbonate) as potential candidates, but lack sufficient laboratory measurements of these and other ammoniated species to make a definitive conclusion. We use the observations of Nix and Hydra to estimate the surface temperature and crystalline H 2 O-ice fraction. We find surface temperatures < 20 K (<70 K with 1- σ error) and 23 K (< 150 K with 1- σ error) for Nix and Hydra, respectively. We find crystalline H 2 O-ice fractions of 78 − 22 + 12 % and > 30% for Nix an Hydra, respectively. New Horizons observed Nix and Hydra twice, about 2–3 hours apart, or 5 and 25% of their respective rotation periods. We find no evidence for rotational differences in the disk-averaged spectra between the two observations of Nix or Hydra. We perform a pixel-by-pixel analysis of Nix’s disk-resolved spectra and find that the surface is consistent with a uniform crystalline H 2 O-ice fraction, and a ∼ 50% variation in the normalized band area of the 2.21 µm band with a minimum associated with the red blotch seen in color images of Nix. Finally, we find evidence for bands on Nix and Hydra at 2.42 and possibly 2.45 µm, which we cannot identify, and, if real, do not appear to be associated with the ammoniated species. We do not detect other ices, such as CO 2 , CH 3 OH and HCN. [ABSTRACT FROM AUTHOR]

Since the end of the Galileo epoch, ground-based observations have been crucial for the continued monitoring and characterization of volcanic activity on Jupiter’s moon, Io. We compile and analyze observations from the Keck and Gemini North telescopes between 2001 and 2016, including new and published observations from 2003, 2004, 2005, 2007, 2008, 2009, 2011, 2012, 2013, and 2016. A total of 88 distinct hot spot sites were detected over the 15-year period, 82 of which were detected multiple times, and 24 of which were not detected by Galileo at thermal infrared wavelengths (1–5 µm). A variety of analytical methods are utilized to investigate the detections of active volcanism as a surface expression of interior heating. Geologic associations of hot spots, including patera type, lava flow type, and proximity to mountainous regions, are made using the USGS-published global geologic map of Io (Williams, 2011). We also provide a summary of outburst-scale events, along with the slightly less bright but more frequent, mini-outbursts described by de Kleer and de Pater (2016a). We investigate the spatial distribution of volcanic activity on Io using nearest neighbor, mean pairwise spacing, and mean latitude statistics with various classification schemes. The analysis confirms previous findings in that the heat dissipation appears to be primarily concentrated in the asthenosphere resulting in a high time-averaged surface heat flux at low latitudes. Our observations show significant spatial deviations do exist from the asthenosphere heat dissipation model while also suggesting a deeper source of magma ascent to be present as well, supporting conclusions from previous analyses of primarily spacecraft data (Veeder et al., 2012; Hamilton, 2013; Davies et al., 2015). From a temporal perspective, there are signs of significant variations in the distribution of global heat flux, as volcanoes undetected, and probably dormant, during the Galileo encounters subsequently erupted and remained active during our observations. We also use the on 3.8-µm radiant intensity timelines of individual hot spots, along with the distribution of extensive lava fields in relation to detected activity, as a means to investigate possible connections between hot spots and short timescale, spatio-temporal variations in the global heat flux distribution. We conclude that while the global heat flux distribution remains relatively constant over decadal timescales, there is evidence that significant deviations do occur potentially as a result of mountain forming processes or triggering mechanisms between eruptions. [ABSTRACT FROM AUTHOR]

The UltraViolet Spectrograph (UVS) and the Jupiter InfraRed Auroral Mapper (JIRAM) observed the north polar aurora before the first perijove of the Juno orbit (PJ1) on 27 August 2016. The UVS bandpass corresponds to the H 2 Lyman and Werner bands that are directly excited by collisions of auroral electrons with molecular hydrogen. The spectral window of the JIRAM L-band imager includes some of the brightest H 3 + thermal features between 3.3 and 3.6 µm. A series of spatial scans obtained with JIRAM every 30 s is used to build up five quasi-global images, each covering ∼12 min. of observations. JIRAM's best spatial resolution was on the order of 50 km/pixel during this time frame, while UVS has a resolution of about 750 km. Most of the observed large-scale auroral features are similar in the two spectral regions, but important differences are also observed in their morphology and relative intensity. Only a part of the UV-IR differences stems from the higher spatial resolution of JIRAM, as some of them are still present following smoothing of the JIRAM images at the UVS resolution. For example, the JIRAM images show persistent narrow arc structures in the 100°–180° S III longitude sector at dusk not resolved in the ultraviolet, but consistent with the structure of in situ electron precipitation measured two hours later. The comparison between the H 2 intensity and the H 3 + radiance measured along two radial cuts from the center of the main emission illustrates the complex relation between the electron energy input, their characteristic energy and the H 3 + emission. Low values of the H 3 + intensity relative to the H 2 brightness are observed in regions of high FUV color ratio corresponding to harder electron precipitation. The rapid loss of H 3 + ions reacting with methane near and below the homopause appears to play a significant role in the control of the relative brightness of the two emissions. Cooling of the auroral thermosphere by H 3 + radiation is spatially variable relative to the direct particle heating resulting from the precipitated electron flux. [ABSTRACT FROM AUTHOR]

SPICAV IR, one channel of SPICAV/SOIR instrument suite onboard Venus Express, performed solar occultation measurements of the atmosphere at terminators in 0.65–1.7 µm spectral range. We analyze the properties of the upper part of the Venus aerosol layer (upper haze, 70 − 95 km altitude) from 798 observations performed from May 2006 through November 2014. Vertical profiles of slant optical depth, extinction coefficient, effective radius, and number density of haze particles from 222 orbits were analyzed in a previous publication (Luginin et al., 2016); their diurnal, latitudinal, and interannual variabilities were investigated. The present paper is devoted to analysis of scale heights and properties of detached haze layers from 147 orbits at mid-to-high northern latitudes, where the best spatial resolution was obtained. Scale heights retrieved from 43 orbits were equal to 4 − 5.5 km at the North Pole (82°N-90°N) decreasing to 2 − 4 km at 60°N − 80°N latitudes. As an explanation of such latitudinal variations, we propose a mechanism based on vertical transport driven by winds that are directed upward at the North Pole and downward at 60°N − 80°N latitudes. Detached layers were detected in 93 occultations at 58°N − 90°N. The detached layers are presumably formed through condensation of water vapor on droplets of sulfuric acid water solution; they were mostly seen at 80 − 88 km at the morning terminator, and at 84 − 90 km at the evening one. This difference in altitude of the detached layers can be explained by diurnal variations in thermal structure of Venusian mesosphere. The vertical optical depth of detached layers varies broadly around the mean τ DL ∼ 0.8 − 3·10 −3 ; no difference between the morning and the evening terminators was observed. The effective radius and number density of aerosol particles in the detached layers group around a very wide maximum at the morning terminator (0.65 ± 0.25 µm and 0.6 ± 0.4 cm −3 ) and two maxima at the evening terminator (0.4 ± 0.1 µm and 0.85 ± 0.15 µm; 0.3 ± 0.2 cm −3 and 4.5 ± 2.5 cm −3 ). This could be explained by differences in initial altitudes at which condensation of particles occurs. [ABSTRACT FROM AUTHOR]

Since its first measurement 20 years ago by the Infrared Space Observatory (ISO), the water (H 2 O) mole fraction in Titan’s stratosphere remains uncertain due to large differences between the determinations from available measurements. More particularly, the recent measurements made from the Herschel observatory (PACS and HIFI) estimated the H 2 O mole fraction to be 0.023 ppb at 12.1 mbar. A mixing ratio of 0.14 ppb at 10.7 mbar was, however, retrieved from nadir spatially-resolved observations of Cassini/CIRS. At the same pressure level (10.7 mbar), this makes a difference of a factor of 5.5 between PACS and CIRS measurements, and this has notably prevented current models from fully constraining the oxygen flux flowing into Titan’s atmosphere. In this work, we try to understand the differences between the H 2 O mole fractions estimated from Herschel/PACS and Cassini/CIRS observations. The strategy for this is to 1) analyse recent disc-averaged observations of CIRS to investigate if the observation geometry could explain the previous observed differences, and 2) (re)analyse the three types of observation with the same retrieval scheme to assess if previous differences in retrieval codes/methodology could be responsible for the previous discrepancies. With this analysis, we show that using the same retrieval method better reconcile the previous measurements of these instruments. However, the addition of the disc-averaged CIRS observations, instead of confirming the consistency between the different datasets, reveals discrepancies between one of the CIRS disc-averaged set of observations and PACS measurements. This raises new questions regarding the possibility of latitudinal variations of H 2 O, which could be triggered by seasonal changes of the meridional circulation. As it has already been shown for nitriles and hydrocarbons, this circulation could potentially impact the latitudinal distribution of H 2 O through the subsidence or upwelling of air rich in H 2 O. The possible influence of spatial/time variations of the OH/H 2 O input flux in Titan’s atmosphere is also discussed. The analysis of more observations will be needed in future work to address the questions arising from this work and to improve the understanding of the sources of H 2 O in Titan’s atmosphere. [ABSTRACT FROM AUTHOR]

We have analyzed the complete archive of the Visual and Infrared Mapping Spectrometer (VIMS) data in order to monitor and analyze the evolution of the clouds and haze coverage at both poles of Titan during the entire Cassini mission. Our objective is to give a cartographic synopsis from a VIMS perspective, to provide a global view of the seasonal evolution of Titan's atmosphere over the poles. We leave the detailed comparison with the Imaging Science Subsystem (ISS) and the Composite Infrared Spectrometer (CIRS) data sets to further studies. We have computed global hyperspectral mosaics for each of the 127 targeted flybys of Titan to produce synthetic color maps emphasizing the main atmospheric features. The north pole appears fully covered by a huge cloud as soon as the first observations in 2004 and up to the equinox in 2009 (Le Mouélic et al., 2012). The northern skies then became progressively clearer, after the circulation turnover in 2009, revealing the underlying lakes and seas to the optical instruments up to 2017. The reverse situation is observed over the south pole, which was mostly clear of such a high obscuring cloud during the first years of the mission, but started to develop a polar cloud in 2012. This feature grew up month after month until the end of the mission in 2017, with a poleward latitudinal extent of 75 °S in 2013 up to 58 °S in April 2017. Thanks to the spectral capabilities of VIMS, we have detected HCN spectral signatures over the north pole in almost all flybys between 2004 and 2008. These HCN signatures started then to show up over the south pole in almost all flybys between 2012 and 2017, so perfectly matching the timing and spatial extent of the northern and southern polar atmospheric features. [ABSTRACT FROM AUTHOR]

We report the detection of a spectral signature observed at 682 cm − 1 by the Cassini Composite Infrared Spectrometer (CIRS) in nadir and limb geometry observations of Titan’s southern stratospheric polar region in the middle of southern fall, while stratospheric temperatures are the coldest since the beginning of the Cassini mission. In the same period, many gases observed in CIRS spectra (C 2 H 2 , HCN, C 4 H 2 , C 3 H 4 , HC 3 N and C 6 H 6 ) are highly enriched in the stratosphere at high southern latitude due to the air subsidence of the global atmospheric circulation and some of these molecules condense at much higher altitude than usually observed for other latitudes. The 682 cm − 1 signature, which is only observed below an altitude of 300 km, is at least partly attributed to the benzene (C 6 H 6 ) ice ν 4 C–H bending mode. While we first observed it in CIRS nadir spectra of the southern polar region in early 2013, we focus here on the study of nadir data acquired in May 2013, which have a more favorable observation geometry. We derived the C 6 H 6 ice mass mixing ratio in 5° latitude bins from the south pole to 65°S and infer the C 6 H 6 cloud top altitude to be located deeper with increasing distance from the pole. We additionally analyzed limb data acquired in March 2015, which were the first limb dataset available after the May 2013 nadir observation, in order to infer a vertical profile of its mass mixing ratio in the 0.1–1 mbar region (250–170 km). We derive an upper limit of ∼1.5 µm for the equivalent radius of pure C 6 H 6 ice particles from the shape of the observed emission band, which is consistent with our estimation of the ice particle size from condensation growth and sedimentation timescales. We compared the ice mass mixing ratio with the haze mass mixing ratio inferred in the same region from the continuum emission of CIRS spectra, and derived that the haze mass mixing ratios are ∼30 times larger than the C 6 H 6 ice mass mixing ratios for all observations. Several other unidentified signatures are observed near 687 and 702 cm − 1 and possibly 695 cm − 1 , which could also be due to ice spectral signatures as they are observed in the deep stratosphere at pressure levels similar to the C 6 H 6 ice ones. We could not reproduce these signatures with pure nitrile ices (HCN, HC 3 N, CH 3 CN, C 2 H 5 CN and C 2 N 2 ) spectra available in the literature except the 695 cm − 1 feature that could possibly be due to C 2 H 3 CN ice. From this tentative detection, we derive the corresponding C 2 H 3 CN ice mass mixing ratio profile and also inferred an upper limit of its gas volume mixing ratio of 2  ×  10 − 7 at 0.01 mbar at 79°S in March 2015. [ABSTRACT FROM AUTHOR]

By means of a varied-shape thermophysical model of Hanuš et al. (2015) that takes into account asteroid shape and pole uncertainties, we analyze the thermal infrared data acquired by the NASA’s Wide-field Infrared Survey Explorer of about 300 asteroids with derived convex shape models. We utilize publicly available convex shape models and rotation states as input for the thermophysical modeling. For more than one hundred asteroids, the thermophysical modeling gives us an acceptable fit to the thermal infrared data allowing us to report their thermophysical properties such as size, thermal inertia, surface roughness or visible geometric albedo. This work more than doubles the number of asteroids with determined thermophysical properties, especially the thermal inertia. In the remaining cases, the shape model and pole orientation uncertainties, specific rotation or thermophysical properties, poor thermal infrared data or their coverage prevent the determination of reliable thermophysical properties. Finally, we present the main results of the statistical study of derived thermophysical parameters within the whole population of main-belt asteroids and within few asteroid families. Our sizes based on TPM are, in average, consistent with the radiometric sizes reported by Mainzer et al. (2016). The thermal inertia increases with decreasing size, but a large range of thermal inertia values is observed within the similar size ranges between D  ∼ 10–100 km. We derived unexpectedly low thermal inertias ( < 20 J m − 2 s − 1 / 2 K − 1 ) for several asteroids with sizes 10 <  D  < 50 km, indicating a very fine and mature regolith on these small bodies. The thermal inertia values seem to be consistent within several collisional families, however, the statistical sample is in all cases rather small. The fast rotators with rotation period P  ≲ 4 h tend to have slightly larger thermal inertia values, so probably do not have a fine regolith on the surface. This could be explained, for example, by the loss of the fine regolith due to the centrifugal force, or by the ineffectiveness of the regolith production(e.g., by the thermal cracking mechanism of Delbo’ et al. 2014). [ABSTRACT FROM AUTHOR]

Ammonia gas has long been assumed to be the main source of condensables for the upper cloud layer on Jupiter, but distinctive spectral features associated with ammonia have been seen only rarely. Since both ammonia and NH 4 SH absorb in the 3 µm region, and widespread absorption in the 3 µm region was present (Sromovsky and Fry, 2010), identification of the 2 µm absorption feature of NH 3 provided an opportunity to clearly establish its presence in Jovian clouds. Baines et al. (2002) succeeded in finding in Near Infrared Mapping Spectrometer (NIMS) observations one feature that had both 2 µm and 3 µm absorption, and many which were known to have absorption at 2.73 µm. They named these Spectrally Identifiable Ammonia Clouds (SIACs). They also argued that these were fresh ammonia clouds that would eventually succumb to some process that would obscure their absorption features. Detection of many more of the 2 µm features was later achieved by New Horizon’s Linear Etalon Imaging Spectral Array (LEISA) instrument, which provided both the spatial and spectral resolution needed to identify these features. Here we report on the first quantitative modeling that uses NIMS spectra over a broad (1–5.2 µm) spectral range and LEISA spectra over a much narrower (1.25–2.5 µm) spectral range to constrain the cloud structure and composition of these rare cloud features and compare them to background clouds. We find that the absorption signature at 2 µm, which is well characterized in LEISA spectra, is relatively subtle and easily matched by model clouds containing spherical particles of ammonia ice with radii of 2–4 µm. The NIMS spectra, which cover both reflected sunlight as well as thermal emission regions are more difficult to model with cloud materials plausibly present in Jupiter’s atmosphere. The best signal/noise spectra obtained from NIMS provide a relatively sparse sampling of the spectrum, which does not establish the detailed shape of the 3 µm absorption region. NIMS SIAC spectra with much denser spectral sampling are limited by much higher noise levels that degrade the features that are key to identifying cloud composition. The structure which best matches the wide range NIMS SIAC spectra contains two overlapping NH 3 clouds with a bi-modal size distribution over an optically thick NH 4 SH cloud. The bi-modal distribution may be a result of modeling non-spherical, possibly fractal aggregate, particles with spheres. [ABSTRACT FROM AUTHOR]

We combine measurements from stellar occultations observed by the Cassini Ultraviolet Imaging Spectrograph (UVIS) and limb scans observed by the Composite Infrared Spectrometer (CIRS) to create empirical atmospheric structure models for Saturn corresponding to the locations probed by the occultations. The results cover multiple locations at low to mid-latitudes between the spring of 2005 and the fall of 2015. We connect the temperature-pressure (T-P) profiles retrieved from the CIRS limb scans in the stratosphere to the T-P profiles in the thermosphere retrieved from the UVIS occultations. We calculate the altitudes corresponding to the pressure levels in each case based on our best fit composition model that includes H 2 , He, CH 4 and upper limits on H. We match the altitude structure to the density profile in the thermosphere that is retrieved from the occultations. Our models depend on the abundance of helium and we derive a volume mixing ratio of 11  ±  2% for helium in the lower atmosphere based on a statistical analysis of the values derived for 32 different occultation locations. We also derive the mean temperature and methane profiles in the upper atmosphere and constrain their variability. Our results are consistent with enhanced heating at the polar auroral region and a dynamically active upper atmosphere. [ABSTRACT FROM AUTHOR]

C/2002 CE 10 is an object in a retrograde elliptical orbit with Tisserand parameter − 0.853 indicating a likely origin in the Oort Cloud. It appears to be a rather inactive comet since no coma and only a very weak tail was detected during the past perihelion passage. We present multi-color optical photometry, lightcurve and thermal mid-IR observations of the asteroidal comet. With the photometric analysis in BVRI , the surface color is found to be redder than asteroids, corresponding to cometary nuclei and TNOs/Centaurs. The time-resolved differential photometry supports a rotation period of 8.19  ±  0.05 h. The effective diameter and the geometric albedo are 17.9  ±  0.9 km and 0.03  ±  0.01, respectively, indicating a very dark reflectance of the surface. The dark and redder surface color of C/2002 CE 10 may be attribute to devolatilized material by surface aging suffered from the irradiation by cosmic rays or from impact by dust particles in the Oort Cloud. Alternatively, C/2002 CE 10 was formed of very dark refractory material originally like a rocky planetesimal. In both cases, this object lacks ices (on the surface at least). The dynamical and known physical characteristics of C/2002 CE 10 are best compatible with those of the Damocloids population in the Solar System, that appear to be exhaust cometary nucleus in Halley-type orbits. The study of physical properties of rocky Oort cloud objects may give us a key for the formation of the Oort cloud and the solar system. [ABSTRACT FROM AUTHOR]

Asteroid (16) Psyche is a unique, metal-rich object belonging to the “M” taxonomic class. It may be a remnant protoplanet that has been stripped of most silicates by a hit-and-run collision. Because Psyche offers insight into the planetary formation process, it is the target of NASA’s Psyche mission, set to launch in 2023. In order to constrain Psyche’s surface properties, we have carried out a mid-infrared (5–14 µm) spectroscopic study using data collected with the Spitzer Space Telescope’s Infrared Spectrograph. Our study includes two observations covering different rotational phases. Using thermophysical modeling, we find that Psyche’s surface is smooth and likely has a thermal inertia Γ = 5–25 J/m 2 /K/s 1/2 and bolometric emissivity ϵ = 0.9, although a scenario with ϵ = 0.7 and thermal inertia up to 95 J/m 2 /K/s 1/2 is possible if Psyche is somewhat larger than previously determined. The smooth surface is consistent with the presence of a metallic bedrock, which would be more ductile than silicate bedrock, and thus may not readily form boulders upon impact events. From comparisons with laboratory spectra of silicate and meteorite powders, Psyche’s 7–14 µm emissivity spectrum is consistent with the presence of fine-grained (< 75 µm) silicates on Psyche’s surface. We conclude that Psyche is likely covered in a fine silicate regolith, which may also contain iron grains, overlying an iron-rich bedrock. [ABSTRACT FROM AUTHOR]

SHERMAN, a new thermophysical modeling package designed for analyzing near-infrared spectra of asteroids and other solid bodies, is presented. The model’s features, the methods it uses to solve for surface and subsurface temperatures, and the synthetic data it outputs are described. A set of validation tests demonstrates that SHERMAN produces accurate output in a variety of special cases for which correct results can be derived from theory. These cases include a family of solutions to the heat equation for which thermal inertia can have any value and thermophysical properties can vary with depth and with temperature. An appendix describes a new approximation method for estimating surface temperatures within spherical-section craters, more suitable for modeling infrared beaming at short wavelengths than the standard method. [ABSTRACT FROM AUTHOR]

We apply a new shape-based thermophysical model, SHERMAN, to the near-Earth asteroid (NEA) 8567 (1996 HW1) to derive surface properties. We use the detailed shape model of Magri et al. (2011) for this contact binary NEA to analyze spectral observations (2–4.1 microns) obtained at the NASA IRTF on several different dates to find thermal parameters that match all the data. Visible and near-infrared (0.8–2.5 microns) spectral observations are also utilized in a self-consistent way. We find that an average visible albedo of 0.33, thermal inertia of 70 (SI units) and surface roughness of 50% closely match the observations. The shape and orientation of the asteroid is very important to constrain the thermal parameters to be consistent with all the observations. Multiple viewing geometries are equally important to achieve a robust solution for small, non-spherical NEAs. We separate the infrared beaming effects of shape, viewing geometry and surface roughness for this asteroid and show how their effects combine. We compare the diameter and albedo that would be derived from the thermal observations assuming a spherical shape with those from the shape-based model. We also discuss how observations from limited viewing geometries compare to the solution from multiple observations. The size that would be derived from the individual observation dates varies by 20% from the best-fit solution, and can be either larger or smaller. If the surface properties are not homogeneous, many solutions are possible, but the average properties derived here are very tightly constrained by the multiple observations, and give important insights into the nature of small NEAs. [ABSTRACT FROM AUTHOR]