CO2 Ice Research Articles

Variation of the sticking of methanol on low-temperature surfaces as a possible obstacle to freeze out in dark clouds

ABSTRACT Sticking of gas-phase methanol on different cold surfaces – gold, 13CO, and amorphous solid water (ASW) ice – was studied as a function of surface temperature (7–40 K). In an ultrahigh-vacuum system, reflection absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption methods were simultaneously used to measure methanol sticking efficiency. Methanol band strengths obtained by RAIRS vary greatly depending on the type of the surface. Nevertheless, both methods indicate that the sticking of methanol on different surfaces varies with surface temperature. The sticking efficiency decreases by 30${{\ \rm per\ cent}}$ as the surface temperature goes from 7 to 16 K, then gradually increases until the temperature is 40 K, reaching approximately the initial value found at 7 K. The sticking of methanol differs slightly from one surface to another. At low temperature, it has the lowest values on gold, intermediate values on water ice, and the highest values are found on CO ice, although these differences are smaller than those observed with temperature variation. There exists probably a turning point during the structural organization of methanol ice at 16 K, which makes the capture of methanol from the gas phase less efficient. We wonder if this observation could explain the surprising high abundance of gaseous methanol observed in dense interstellar cores, where it should accrete on grains. In this regard, a 30${{\ \rm per\ cent}}$ reduction of the sticking is not sufficient in itself but transposed to astrophysical conditions dominated by cold gas (∼15 K), which could reduce the sticking efficiency by two orders of magnitude.

Formation of long-distance water ice avalanches on Mars

At the high northern latitudes of Mars, there are two impact craters (70.3°N 266.45°E and 67.25°N 249.45°E) with lobate moraine-like ridges (LMLR) on the inner slopes. In addition to these craters, a nearby plain (74°N 95°E) also displays remnants of water ice layered deposits with similar series of lobate ridges. The formation of these ridges has been hypothesized to be caused by either viscoplastic flow of CO2 ice deposits or a catastrophic down-slope movement of an H2O ice massif, which produced long-distance avalanches or fast-running glacier surges. In past climatic epochs, the formation of water ice massifs on high latitudes was possible under low (<20°) planet obliquity. Destabilization of water ice massifs on the craters’ steep inner slopes could lead to down-slope movement, followed by the destruction of the massifs and the production of long-distance water ice avalanches or surges. In this work, we focus on the avalanche formation hypothesis. The down-slope movement of a water ice massif has several possible causes, with the main one being excessive accumulation of water ice on slopes, which then reaches a critical unstable condition. Modeling of long-distance avalanche processes in Martian environments was carried out with Rapid Mass Movement Simulation (RAMMS:AVALANCHE) software, using the graph-analytical method of estimating avalanche velocity and maximum distance. As a result of the modeling, the volume of down-slope movement was defined, confirming the that LMLR were formed by the catastrophic down-slope movement of H2O ice masses in the form of long-distance avalanches.

Hardness and Yield Strength of CO Ice Under Martian Temperature Conditions

AbstractAlthough ice fracturing and deformation is key to understanding some of the landforms encountered in the high‐latitude regions on Mars and on other icy bodies in the solar system, little is known about the mechanical characteristics of CO ice. We have measured the hardness of solid CO ice directly in the laboratory with a Leeb hardness tester and calculated the corresponding yield strength. We have also measured the hardness of water ice by the same method, confirming previous work. Our results indicate that CO ice is slightly weaker, ranging between Leeb 200 and 400 ( 10 and 30 MPa yield strength, assuming only plastic deformation and no strain hardening during the experiment), for typical Martian temperatures. Our results can be used for models of CO ice rupture (depending on the deformation timescales) explaining surface processes on Mars and solar system icy bodies.

Phoebe's carbon isotope composition as evidence for self-shielding in the solar nebula

Clark et al. [Clark, R.N., Brown, R.H., Cruikshank, D.P., Swayze, G.A., 2019. Icarus, 321, 791–802] reported an extremely low value of the 12C/13C ratio in CO2 ice on Phoebe, a likely captured moon of Saturn. Unless Phoebe did not form in the solar system, we interpret this value as indication that Phoebe accreted surface carbon from a region of the protosolar nebula where 13C was enriched due to self-shielding of 12CO from photodissociation. This could imply that Phoebe is also enriched in 17,18O relative to most solar system objects sampled to date. Phoebe and other objects that may have sampled these 13C-rich regions, such as Pallas or Triton, may provide the opportunity to directly measure isotopic fractionations in endmembers of the self-shielded solar nebula.

Internal Structure and CO2 Reservoirs of Habitable Water Worlds

Abstract Water worlds are water-rich (&gt;1 wt% H2O) exoplanets. The classical models of water worlds considered layered structures determined by the phase boundaries of pure water. However, water worlds are likely to possess comet-like compositions, with between ∼3 and 30 mol% CO2 relative to water. In this study, we build an interior structure model of habitable (i.e., surface liquid ocean–bearing) water worlds using the latest results from experimental data on the CO2–H2O system to explore the CO2 budget and localize the main CO2 reservoirs inside of these planets. We show that CO2 dissolved in the ocean and trapped inside of a clathrate layer cannot accommodate a cometary amount of CO2 if the planet accretes more than 11 wt% of volatiles (CO2 + H2O) during its formation. If the atmosphere holds more than a negligible amount of the CO2 (&gt;0.01% of the planet mass), the planet will not have a habitable surface temperature. We propose a new, potentially dominant, CO2 reservoir for water worlds: CO2 buried inside of the high-pressure water ice mantle as CO2 ices or (H2CO3 · H2O), the monohydrate of carbonic acid. If insufficient amounts of CO2 are sequestered in either this reservoir or the planet’s iron core, habitable-zone water worlds could generically be stalled in their cooling before liquid oceans have a chance to condense.

On the activity of comets: understanding the gas and dust emission from comet 67/Churyumov–Gerasimenko’s south-pole region during perihelion

ABSTRACT When comets approach the Sun, their surface is heated and the volatile species start to sublimate. Due to the increasing gas pressure, dust is ejected off the surface, which can be observed as cometary coma, dust tail, and trail. However, the underlying physical processes are not fully understood. Using state-of-the-art results for the transport of heat and gas as well as of the mechanical properties of cometary matter, we intend to describe the activity pattern of comets when they approach the Sun. We developed a novel thermophysical model to simulate the dust ejection from comet 67/Churyumov–Gerasimenko’s south-pole region at perihelion. Based on the input parameters, this model computes the sub-surface temperature profile, the pressure build-up, and the redistribution of volatiles inside the cometary sub-surface region and provides mass-loss rates of dust and gas as well as typical sizes and ice content of the ejected dust chunks. Our thermophysical model allows for continuous gas and dust ejection from the Southern hemisphere of comet 67/Churyumov–Gerasimenko at perihelion. We find that the model output is in general agreement with the observed Rosetta data. The sublimation of CO2 ice drives the ejection of very large ($\gtrsim 10\, \mathrm{cm}$) chunks, which contain $10\, {{\ \rm per\ cent}}$ to $90 \, {{\ \rm per\ cent}}$ of the initial water–ice content. In contrast, the outgassing of H2O ice causes the lift-off of small clusters of dust aggregates, which contain no ice.

Effects of 150–1000 eV Electron Impacts on Pure Carbon Monoxide Ices Using the Interstellar Energetic-Process System (IEPS)

Abstract Pure CO ice has been irradiated with electrons of energy in the range 150−1000 eV with the Interstellar Energetic-Process System. The main products of irradiation are carbon chains C n (n = 3, 5, 6, 8, 9, 10, 11, 12), suboxides, C n O (n = 2, 3, 4, 5, 6, 7), and C n O2 (n = 1, 3, 4, 5, 7) species. CO2 is by far the most abundant reaction product in all the experiments. The destruction cross section of CO peaks at about 250 eV, decreases with the energy of the electrons and is more than one order of magnitude higher than for gas-phase CO ionization. The production cross section of carbon dioxide has been also derived and is characterized by the competition between chemistry and desorption. Desorption of CO and of new species during the radiolysis follows the electron distribution in the ice. Low-energy electrons having short penetration depths induce significant desorption. Finally, as the ice thickness approaches the electron penetration depth the abundance of the products starts to saturate. Implications on the atmospheric photochemistry of cold planets hosting surface CO ices are also discussed.

Debris accumulations of CO2 ice in the south polar residual cap of mars: Longevity and processes

The Residual South Polar Cap (RSPC) of Mars is a thin covering of CO2 ice resting on water-ice rich deposits. As such, it is a likely indicator of the net effects of recent polar climate. This covering has had minor changes in outline for the period of spacecraft observation (Piqueux and Christensen, 2008a) and estimates of its recent mass balance suggest fractionally small changes in its volume (Thomas et al., 2016). Pit growth by scarp retreat (Malin et al., 2001; Byrne and Ingersoll, 2003a; Thomas et al., 2005, 2013) is a major, relatively easily measured component of the cap's mass balance. This scarp retreat is only the beginning of a process: fracturing, slumping, and sublimation (Byrne et al., 2008; Thomas et al., 2009) lead to production of a trail of debris. This study focuses on that debris using spacecraft imaging data. The rough, relatively dark debris forms ubiquitous ramps, typically tens of m wide, around scarps within pits or on perimeters of mesas. Much wider accumulations of debris, “debris fields,” mimic distinctive scalloped outlines of mesas and are observed to originate by merging of expanding pits within a mesa. The subsequent evolution of debris fields includes repeated year-to-year local relief inversions that involve trapping and retention of seasonal ice in low areas that effectively reduce the vertical loss rates. Complete loss of the CO2 debris from a surface of water-ice rich Polar Layered Deposits (PLD) can initiate new net accumulation of CO2 ice. The longevity of some debris fields, essentially instances of slow downwasting, appear to facilitate relief inversion on large scales by allowing the surrounding areas to accumulate new CO2 ice and to thicken relative to the debris fields.

A multiannual record of gravity wave activity in Mars’s lower atmosphere from on-planet observations by the Mars Climate Sounder

Gravity waves in Mars’s atmosphere strongly affect the general circulation as well as middle atmospheric cloud formation, but the climatology and sources of gravity waves in the lower atmosphere remain poorly understood. At Earth, the statistical variance in satellite observations of thermal emission above the instrumental noise floor has been used to enable measurement of gravity wave activity at a global scale. Here is presented an analysis of variance in calibrated radiance at 15.4μm (635–665 cm−1) from off-nadir and nadir observations by the Mars Climate Sounder (MCS) on board Mars Reconnaissance Orbiter (MRO); a major expansion in the observational data available for validating models of Martian gravity wave activity. These observations are sensitive to gravity waves at 20–30 km altitude with wavelength properties (λh=10–100 km, λz> 5 km) that make them likely to affect the dynamics of the middle and upper atmosphere. We find that: (1) strong, moderately intermittent gravity wave activity is scattered over the tropical volcanoes and throughout the middle to high latitudes of both hemispheres during fall and winter, (2) gravity wave activity noticeably departs from climatology during regional and global dust storms; and (3) strong, intermittent variance is observed at night in parts of the southern tropics during its fall/winter, but frequent CO2 ice clouds prevents unambiguous attribution to GW activity. The spatial distribution of wave activity is consistent with topographic sources being dominant, but contributions from boundary layer convection and other convective processes are possible.

Formation of Halogen-bearing Species. II. Irradiation of Chloromethane in Carbon Monoxide Ice with VUV Light and Electrons

Abstract The synthesis of chlorine-bearing species in CO ice was studied by the irradiation of CH3Cl:CO ice at 10 K with vacuum-ultraviolet (VUV) light and energetic electrons. In contrast to the photochemical behavior of CH3F:CO ice, photolysis of CH3Cl:CO ice with Lyα or broadband VUV light afforded various products. This discrepancy was attributed to the abundant absorption bands of CH3Cl in the VUV region, particularly in the Lyα region. The Cl-bearing species including Cl2O, ClCO, C3Cl2, C3HCl, and HOOCl were characterized by observing their IR features. In contrast, electron bombardment of ice mixtures produced various carbon oxides and primary products, such as CH2Cl and HCO. In addition, the mechanism of energetic processes in electron bombardment was discussed.

OUP accepted manuscript

One of the key findings of the Rosetta's mission to the Jupiter family comet 67P/Churyumov-Gerasimenko was its peculiar bilobed shape along with the apparent north/south dichotomy in large scale morphology. This has re-ignited scientific discussions on the topic of origin, evolution and age of the nucleus. In this work we set up a general numerical investigation on the role of solar driven activity on the overall shape change. Our goal is to isolate and study the influence of key parameters for solar driven mass loss, and hopefully obtain a classification of the final shapes. We consider five general classes of three-dimensional (3D) objects for various initial conditions of spin-axis and orbital parameters, propagating them on different orbits accounting for solar driven CO ice sublimation. A detailed study of the coupling between sublimation curve and orbital parameters (for CO and H$_{2}$O ices) is also provided. The idealizations used in this study are aimed to remove the ad-hoc assumptions on activity source distribution, composition, and/or chemical inhomogeneities as applied in similar studies focusing on explaining a particular feature or observation. Our numerical experiments show that under no condition a homogeneous nucleus with solar driven outgassing can produce concave morphology on a convex shape. On the other hand, preexisting concavities can hardly be smoothed/removed for the assumed activity. In summary, the coupling between solar distance, eccentricity, spin-axis and its orientation, as well as effects on shadowing and self-heating do combine to induce morphology changes that might not be deducible without numerical simulations.

Impact of surface Albedo on Martian photochemistry

Solar energy is the primary driving force behind a planet’s climate system, and surface albedo plays a key role in determining the energy budget of the planet. Coupling the Snow, Ice, and Aerosol Radiation (SNICAR) with the Laboratoire de Meteorologie Dynamique (LMD) Mars General Circulation Model (MGCM) to create a new coupled model leads to an approximately 4% drop in the net CO2 ice deposition on Mars. Newly simulated surface albedo affects the concentration of gaseous species in the Martian atmosphere (condensation-sublimation cycle). The new set-up also impacts the solar energy available in the atmosphere. These two effects together lead to subsequent and significant changes in other chemical species in the Martian atmosphere. Compared with results of the MGCM model alone, in the new coupled model CO2 (gas) and O3 show a drop of about 1.17% and 8.59% in their respective concentrations, while H2O (vapor) and CO show an increase of about 13.63% and 0.56% in their respective concentrations. Among trace species, OH shows a maximum increase of about 29.44%, while the maximum drop of 11.5% is observed in the O concentration. Photochemically neutral species such as Ar and N2 remain unaffected by the albedo changes.

Coevolution of Mars’s atmosphere and massive south polar CO2 ice deposit

A massive CO2 ice deposit overlies1 part of Mars’s primarily H2O ice2–4 south polar cap5. This deposit rivals the mass of Mars’s current, 96% CO2, atmosphere6. Its release could substantially alter Mars’s pressure and climate1. The deposit consists of alternating CO2 and H2O ice layers to a depth of up to approximately 1 km (refs. 1,7,8). The top layer is an enigmatic9–11 1–10 m covering of perennial surface CO2 ice12 called the residual south polar cap. Typical explanations of the layering invoke orbital cycles1,7. Up to now, models assumed that the H2O ice layers insulate and seal in the CO2, allowing it to survive high-obliquity periods7,13. However, these models do not quantitatively predict the deposit’s stratigraphy or explain the residual south polar cap’s existence. Here we present a model in which the deposit’s near-surface CO2 can instead exchange with the atmosphere through permeable H2O ice layers. Using currently observed albedo14,15 and emissivity16 properties of the Martian polar CO2 ice deposits, our model predicts that the present massive CO2 ice deposit is a remnant of larger CO2 ice deposits laid down during periods of decreasing obliquity that are ablated, liberating a residual lag layer of H2O ice, when obliquity increases. Fractions of previous CO2 deposits remain as layers because the amplitudes of the obliquity maxima have been mostly decreasing during the past ~510 kyr (ref. 17). Our model simultaneously explains the observed massive CO2 ice deposit stratigraphy, the residual south polar cap’s existence and the presence of a massive CO2 ice deposit only in the south. We use our model to calculate Mars’s pressure history and determine that the massive CO2 ice deposit is 510 kyr old. The long-term evolution and stratigraphy of the CO2 ice residual southern polar cap of Mars can be explained by a model that includes the active coupling of near-surface CO2 with the atmosphere through the permeable H2O ice layers.

The dry and carbon-poor inner disk of TW Hydrae: evidence for a massive icy dust trap

Context. Gas giants accrete their envelopes from the gas and dust of proto-planetary disks, and therefore it is important to determine the composition of the inner few astronomical units, where most giant planets are expected to form. Aims. We aim to constrain the elemental carbon and oxygen abundance in the inner disk (R &lt; 2.3 AU) of TW Hya and compare with the outer disk (R &gt; 2.3 AU) where carbon and oxygen appear underabundant by a factor of approximately 50. Methods. Archival Spitzer-IRS and VLT-CRIRES observations of TW Hya were compared with a detailed thermo-chemical model, DALI. The inner disk gas mass and elemental C and O abundances were varied to fit the mid-infrared H2 and H2O line fluxes as well as the near-infrared CO line flux. Results. Best-fitting models have an inner disk that has a gas mass of 2 × 10−4 M⊙ with C/H ≈ 3 × 10−6 and O/H ≈ 6 × 10−6. The elemental oxygen and carbon abundances of the inner disk are about 50 times lower than in the interstellar medium and are consistent with those found in the outer disk. Conclusions. The uniformly low volatile abundances imply that the inner disk is not enriched by ices on drifting bodies that evaporate. This indicates that drifting grains are stopped in a dust trap outside the water ice line. Such a dust trap would also form a cavity as seen in high-resolution submillimeter continuum observations. If CO is the major carbon carrier in the ices, dust needs to be trapped efficiently outside the CO ice line of ∼20 AU. This would imply that the shallow submillimeter rings in the TW Hya disk outside of 20 AU correspond to very efficient dust traps. The most likely scenario is that more than 98% of the CO has been converted into less volatile species, for example CO2 and CH3OH. A giant planet forming in the inner disk would be accreting gas with low carbon and oxygen abundances as well as very little icy dust, potentially leading to a planet atmosphere with strongly substellar C/H and O/H ratios.

Detailed characterization of low activity comet 49P/Arend–Rigaux

Comet 49P/Arend–Rigaux is a well known low-activity Jupiter Family comet. Despite the low activity, we have witnessed outgassing activity in 1992, 2004, and 2012. In 2012 a broad tail-like feature (PA ∼ 270°, ∼2.3×105 km) and a narrow jet-like feature (PA ∼ 180°, ∼9.3×104 km) were seen simultaneously. Using Finson–Probstein (FP) dust dynamical models we determine: the grain sizes released in each event; the duration of activity; when the activity peaked; and the velocity of the dust particles, allowing us to make comparisons between the events. We find that the tail feature in 2012 is similar to the tail in 1992 with large grains (40–4000 μm) peaking in activity around perihelion with a long duration of outgassing greater than 150 days. The jet feature from 2012, however, is more similar to the 2004 event which we model with small grains (1–8 μm) with a short duration of activity on the order of one month. The main difference between these two features is that the 2004 event occurs prior to perihelion, while the 2012 event is post-perihelion. We use the grain sizes from the FP models to constrain ice sublimation models. Between 1985 and 2018 we cover six apparitions with 26 nights of our own observations, data from the literature, and data from the Minor Planet Center, which together, allow us to model the heliocentric light curve. We find that the models are consistent with H2O ice sublimation as the volatile responsible for driving activity over most of the active phases and a combination of H2O and CO2 ices are responsible for driving activity near perihelion. We measure the fractional active area over time for H2O and discover that the activity decreases from an average active area of ∼3% to ∼0.2%. This clear secular decrease in activity implies that the comet is becoming depleted of volatiles and is in the process of transitioning to either a dormant or dead state.

Probing the regoliths of the classical Uranian satellites: Are their surfaces mantled by a layer of tiny H2O ice grains?

We investigate whether the surfaces of the classical moons of Uranus are compositionally stratified, with a thin veneer of mostly tiny H2O ice grains (≤2 μm diameters) mantling a lower layer composed of larger grains of H2O ice, dark material, and CO2 ice (~10–50 μm diameters). Near-infrared observations (~1–2.5 μm) have determined that the H2O ice-rich surfaces of these moons are overprinted by concentrated deposits of CO2 ice, found almost exclusively on their trailing hemispheres. However, best fit spectral models of longer wavelength datasets (~3–5 μm) indicate that the spectral signature of CO2 ice is largely absent, and instead, the exposed surfaces of these moons are composed primarily of tiny H2O ice grains. To investigate possible compositional layering of these moons, we have collected new data using the Infrared Array Camera (IRAC) onboard the Spitzer Space Telescope (~3–5 μm). Spectral modeling of these new data is consistent with prior analyses, suggesting that the exposed surfaces of the Uranian moons are primarily composed of tiny H2O ice grains. Furthermore, analysis of these new data reveal that the trailing hemispheres of these moons are brighter than their leading hemispheres over the 3 to 5 μm wavelength range, except for Miranda, which displays no hemispherical asymmetries in its IRAC albedos. Our analyses also reveal that the surface of Ariel displays five distinct, regional-scale albedo zones, possibly consistent with the spatial distribution of CO2 ice on this moon. We discuss possible processes that could be enhancing the observed leading/trailing albedo asymmetries exhibited by these moons, as well as processes that could be driving the apparent compositional stratification of their near surfaces.

Entrapment of CO in CO2 Ice

Abstract Planet atmosphere and hydrosphere compositions are fundamentally set by accretion of volatiles, and therefore by the division of volatiles between gas and solids in planet-forming disks. For hyper-volatiles such as CO, this division is regulated by volatile sublimation energies, and by the ability of other ice components to entrap. Water ice is known for its ability to trap CO and other volatile species. In this study we explore whether another common interstellar and cometary ice component, CO2, is able to trap CO as well. We measure entrapment of CO molecules in CO2 ice through temperature-programmed desorption experiments on CO2:CO ice mixtures. We find that CO2 ice traps CO with a typical efficiency of 40%–60% of the initially deposited CO molecules for a range of ice thicknesses between 7 and 50 monolayers, and ice mixture ratios between 1:1 and 9:1. The entrapment efficiency increases with ice thickness and CO dilution. We also run analogous H2O:CO experiments and find that under comparable experimental conditions, CO2 ice entraps CO more efficiently than H2O ice up to the onset of CO2 desorption at ∼70 K. We speculate that this may be due to different ice restructuring dynamics in H2O and CO2 ices around the CO desorption temperature. Importantly, in planet-forming disks, the ability of CO2 to entrap CO may change the expected division between gas and solids for CO and other hyper-volatiles exterior to the CO2 snowline.

Broadband spectroscopy of astrophysical ice analogues

Context.Reliable, directly measured optical properties of astrophysical ice analogues in the infrared and terahertz (THz) range are missing from the literature. These parameters are of great importance to model the dust continuum radiative transfer in dense and cold regions, where thick ice mantles are present, and are necessary for the interpretation of future observations planned in the far-infrared region.Aims.Coherent THz radiation allows for direct measurement of the complex dielectric function (refractive index) of astrophysically relevant ice species in the THz range.Methods.We recorded the time-domain waveforms and the frequency-domain spectra of reference samples of CO ice, deposited at a temperature of 28.5 K and annealed to 33 K at different thicknesses. We developed a new algorithm to reconstruct the real and imaginary parts of the refractive index from the time-domain THz data.Results.The complex refractive index in the wavelength range 1 mm–150μm (0.3–2.0 THz) was determined for the studied ice samples, and this index was compared with available data found in the literature.Conclusions.The developed algorithm of reconstructing the real and imaginary parts of the refractive index from the time-domain THz data enables us, for the first time, to determine the optical properties of astrophysical ice analogues without using the Kramers–Kronig relations. The obtained data provide a benchmark to interpret the observational data from current ground-based facilities as well as future space telescope missions, and we used these data to estimate the opacities of the dust grains in presence of CO ice mantles.

The REASONS Survey: Resolved Millimeter Observations of a Large Debris Disk around the Nearby F Star HD 170773

Abstract Debris disks are extrasolar analogs to our own Kuiper Belt and they are detected around at least 17% of nearby Sun-like stars. The morphology and dynamics of a disk encode information about its history, as well as that of any exoplanets within the system. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to obtain 1.3 mm observations of the debris disk around the nearby F5V star HD 170773. We image the face-on ring and determine its fundamental parameters by forward-modeling the interferometric visibilities through a Markov Chain Monte Carlo approach. Using a symmetric Gaussian surface density profile, we find a 71 ± 4 au wide belt with a radius of au, a relatively large radius compared with most other millimeter-resolved belts around late A/early F type stars. This makes HD 170773 part of a group of four disks around A and F stars with radii larger than expected from the recently reported planetesimal belt radius—stellar luminosity relation. Two of these systems are known to host directly imaged giant planets, which may point to a connection between large belts and the presence of long-period giant planets. We also set upper limits on the presence of CO and CN gas in the system, which imply that the exocomets that constitute this belt have CO and HCN ice mass fractions of &lt;77% and &lt;3%, respectively. This is consistent with solar system comets and other exocometary belts.

New and extended data processing of Mars Odyssey Neutron Spectrometer data

The Los Alamos National Laboratory designed and built Mars Odyssey Neutron Spectrometer (MONS) has been operating and collecting data from February 2002 to the present. MONS measures the neutron leakage albedo from galactic cosmic ray bombardment of Mars. These signals can indicate the presence of near-surface water deposits on Mars, and can also be used to study properties of the seasonal polar CO2 ice caps. This work outlines a new analysis of the MONS data that results in new and extended time-series maps of MONS thermal and epithermal neutron data. The new data are compared to previous publications on the MONS instrument. We then present preliminary results studying the inter-annual variability in the polar regions of Mars based on 8 Mars-Years of MONS data from the new dataset.