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Volatiles and refractories represent the two end-members in the volatility range of species in any surface-bounded exosphere. Volatiles include elements that do not interact strongly with the surface, such as neon (detected on the Moon) and helium (detected both on the Moon and at Mercury), but also argon, a noble gas (detected on the Moon) that surprisingly adsorbs at the cold lunar nighttime surface. Refractories include species such as calcium, magnesium, iron, and aluminum, all of which have very strong bonds with the lunar surface and thus need energetic processes to be ejected into the exosphere. Here we focus on the properties of species that have been detected in the exospheres of inner Solar System bodies, specifically the Moon and Mercury, and how they provide important information to understand source and loss processes of these exospheres, as well as their dependence on variations in external drivers.

Although solar-analog stars have been studied extensively over the past few decades, most of these studies have focused on visible wavelengths, especially those identifying solar-analog stars to be used as calibration tools for observations. As a result, there is a dearth of well-characterized solar analogs for observations in the near-infrared, a wavelength range important for studying solar system objects. We present 184 stars selected based on solar-like spectral type and V-J and V-K colors whose spectra we have observed in the 0.8-4.2 micron range for calibrating our asteroid observations. Each star has been classified into one of three ranks based on spectral resemblance to vetted solar analogs. Of our set of 184 stars, we report 145 as reliable solar-analog stars, 21 as solar analogs usable after spectral corrections with low-order polynomial fitting, and 18 as unsuitable for use as calibration standards owing to spectral shape, variability, or features at low to medium resolution. We conclude that all but 5 of our candidates are reliable solar analogs in the longer wavelength range from 2.5 to 4.2 microns. The average colors of the stars classified as reliable or usable solar analogs are V-J=1.148, V-H=1.418, and V-K=1.491, with the entire set being distributed fairly uniformly in R.A. across the sky between -27 and +67 degrees in decl., 19 pages, 8 figures, 2 tables

Mercury is surrounded by a tenuous, collisionless exosphere where the surface of the planet is directly exposed to the space environment. As a consequence, impacts and space weathering processes are expected to eject atoms and molecules from the surface into the exosphere, implying a direct link between the exospheric composition and the planet's regolith material. However, observational evidence demonstrating this link has been elusive. Here we report that exospheric magnesium, a species recently discovered and systematically measured by the Mercury Surface, Space ENvironment, GEochemistry, and Ranging mission, is enhanced when observed over a portion of the planet's surface regolith rich in magnesium. These observations confirm a direct link between Mercury's magnesium exosphere and the underlying crustal surface composition, providing strong evidence supporting theoretical arguments that impact vaporization can directly supply material to the exosphere from the regolith of a rocky, airless body.

We present H$_2$O production rates for comet C/2012 S1 (ISON) derived from observations of [OI] and OH emission during its inbound leg, covering a heliocentric distance range of 1.8-0.44 AU. Our production rates are in agreement with previous measurements using a variety of instruments and techniques and with data from the various observatories greatly differing in their projected fields of view. The consistent results across all data suggest the absence of an extended source of H$_2$O production, for example sublimation of icy grains in the coma, or a source with spatial extent confined to the dimensions of the smallest projected field of view (in this case $ 1.2 AU, which then decreased to about half this value from R$_h$=1.2-0.9 AU. This was followed by a rapid increase in active area at about R$_h$=0.6 AU, corresponding to the first of three major outbursts ISON experienced inside of 1 AU. The combination of a detected outburst in the light curve and rapid increase in active area likely indicates a major nucleus fragmentation event. The 5-10 km$^2$ active area observed outside of R$_h$=0.6 AU is consistent with a 50-100% active fraction for the nucleus, larger than typically observed for cometary nuclei. Although the absolute value of the active area is somewhat dependent on the thermal model employed, the changes in active area observed are consistent among models. The conclusion of a 50-100+% active fraction is robust for realistic thermal models of the nucleus. However the possibility of a contribution of a spatially unresolved distribution of icy grains cannot be discounted., Comment: 26 pages, 5 figures, 5 tables, accepted for publication in Icarus

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.

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.

We present thermal properties and an improved shape model for potentially hazardous asteroid (162421) 2000 ET70. In addition to the radar data from 2000 ET70's apparition in 2012, our model incorporates optical lightcurves and infrared spectra that were not included in the analysis of Naidu et al. (2013, Icarus 226, 323-335). We confirm the general "clenched fist" appearance of the Naidu et al. model, but compared to their model, our best-fit model is about 10% longer along its long principal axis, nearly identical along the intermediate axis, and about 25% shorter along the short axis. We find the asteroid's dimensions to be 2.9 km $\times$ 2.2 km $\times$ 1.5 km (with relative uncertainties of about 10%, 15%, and 25%, respectively). With the available data, 2000 ET70's period and pole position are degenerate with each other. The radar and lightcurve data together constrain the pole direction to fall along an arc that is about twenty-three degrees long and eight degrees wide. Infrared spectra from the NASA InfraRed Telescope Facility (IRTF) provide an additional constraint on the pole. Thermophysical modeling, using our SHERMAN software, shows that only a subset of the pole directions, about twelve degrees of that arc, are compatible with the infrared data. Using all of the available data, we find that 2000 ET70 has a sidereal rotation period of 8.944 hours ($\pm$ 0.009 h) and a north pole direction of ecliptic coordinates $(52^{\circ}, -60^{\circ}) \pm 6^{\circ}$. The infrared data, acquired over several dates, require that the thermal properties (albedo, thermal inertia, surface roughness) must change across the asteroid's surface. By incorporating the detailed shape model and spin state into our thermal modeling, the multiple ground-based observations at different viewing geometries have allowed us to constrain the levels of the variations in the surface properties., Revised and submitted to Icarus; 22 pages, 13 figures; 51 supplementary figures (in a 25MB PDF) can be found at http://astro.cornell.edu/~seanm/2000et70/

We present our shape model of Amor class near-Earth asteroid (1627) Ivar. During Ivar's apparition in 2013, in which it had a minimum distance of 0.32 AU, we obtained both CCD photometry and radar observations. The radar data consist of echo power spectra and delay-Doppler imaging with 300 m resolution and were obtained using the Arecibo Observatory's 2380 MHz radar. Lightcurve data were gathered using the 0.35 m telescope at the Palmer Divide Station. Using these data, we constructed a detailed shape model of Ivar that reveals more surface detail than earlier models. Ivar was found to have a rotational period of 4.7951689 ± 0.0000026 hours with a pole located within 6° of ecliptic longitude and latitude 336° and 37° respectively. Ivar is an elongated asteroid with maximum extensions along the three body-fixed coordinates being 15.15 × 6.25 × 5.66 km ± 10%. The results of surface slope analysis suggest that Ivar is covered with a loose regolith. Ivar appears to reside in, or near, an optimum state with respect to its shape, spin, and bulk density, such that dynamic topography, surface slopes, and erosion rates on the body are near minimum levels and is therefore dynamically stable.

International audience; Understanding the cosmogonic record encoded in the parent volatiles stored in cometary nuclei requires investigating whether evolution (thermal or otherwise) has modified the composition of short-period comets during successive perihelion passages. As the most volatile molecules systematically observed in comets, the abundances of CO, CH 4 , and C 2 H 6 in short-period comets may serve to elucidate the interplay between natal conditions and post-formative evolution in setting present-day composition, yet secure measurements of CO and CH 4 in Jupiterfamily comets (JFCs) are especially sparse. The highly favorable 2018 apparition of JFC 21P/Giacobini-Zinner enabled a sensitive search for these "hypervolatiles" in a prototypical carbon-chain depleted comet. We observed 21P/Giacobini-Zinner with the iSHELL spectrograph at the NASA Infrared Telescope Facility on four preperihelion dates, two dates near-perihelion, and one post-perihelion date. We obtained detections of CO, CH 4 , and C 2 H 6 simultaneously with H 2 O on multiple dates. We present rotational temperatures, production rates, and mixing ratios. Combined with previous work, our results may indicate that the hypervolatile coma composition of 21P/ Giacobini-Zinner was variable across apparitions as well as within a particular perihelion passage, yet the spread in these measurements is a relatively small fraction of the variation in each molecule from comet to comet. We discuss the implications of our measured hypervolatile content of 21P/Giacobini-Zinner for the evolution of JFCs, and place our results in the context of findings from the Rosetta mission and ground-based studies of comets.

We report here time domain infrared spectroscopy and optical photometry of the HD145263 silica-rich circumstellar disk system taken from 2003 through 2014. We find an F4V host star surrounded by a stable, massive 1e22 - 1e23 kg (M_Moon to M_Mars) dust disk. No disk gas was detected, and the primary star was seen rotating with a rapid ~1.75 day period. After resolving a problem with previously reported observations, we find the silica, Mg-olivine, and Fe-pyroxene mineralogy of the dust disk to be stable throughout, and very unusual compared to the ferromagnesian silicates typically found in primordial and debris disks. By comparison with mid-infrared spectral features of primitive solar system dust, we explore the possibility that HD 145263's circumstellar dust mineralogy occurred with preferential destruction of Fe-bearing olivines, metal sulfides, and water ice in an initially comet-like mineral mix and their replacement by Fe-bearing pyroxenes, amorphous pyroxene, and silica. We reject models based on vaporizing optical stellar megaflares, aqueous alteration, or giant hypervelocity impacts as unable to produce the observed mineralogy. Scenarios involving unusually high Si abundances are at odds with the normal stellar absorption near-infrared feature strengths for Mg, Fe, and Si. Models involving intense space weathering of a thin surface patina via moderate (T < 1300 K) heating and energetic ion sputtering due to a stellar superflare from the F4V primary are consistent with the observations. The space weathered patina should be reddened, contain copious amounts of nanophase Fe, and should be transient on timescales of decades unless replenished., 41 Pages, 5 Figures, 5 Tables, Accepted for publication in the Astrophysical Journal

The upper atmosphere of Uranus has been observed to be slowly cooling between 1993 and 2011. New analysis of near-infrared observations of emission from H 3 + obtained between 2012 and 2018 reveals that this cooling trend has continued, showing that the upper atmosphere has cooled for 27 years, longer than the length of a nominal season of 21 years. The new observations have offered greater spatial resolution and higher sensitivity than previous ones, enabling the characterization of the H 3 + intensity as a function of local time. These profiles peak between 13 and 15 h local time, later than models suggest. The NASA Infrared Telescope Facility iSHELL instrument also provides the detection of a bright H 3 + signal on 16 October 2016, rotating into view from the dawn sector. This feature is consistent with an auroral signal, but is the only of its kind present in this comprehensive dataset. This article is part of a discussion meeting issue ‘Advances in hydrogen molecular ions: H 3 + , H 5 + and beyond’.

The Neptune Odyssey mission concept is a Flagship-class orbiter and atmospheric probe to the Neptune–Triton system. This bold mission of exploration would orbit an ice-giant planet to study the planet, its rings, small satellites, space environment, and the planet-sized moon Triton. Triton is a captured dwarf planet from the Kuiper Belt, twin of Pluto, and likely ocean world. Odyssey addresses Neptune system-level science, with equal priorities placed on Neptune, its rings, moons, space environment, and Triton. Between Uranus and Neptune, the latter is unique in providing simultaneous access to both an ice giant and a Kuiper Belt dwarf planet. The spacecraft—in a class equivalent to the NASA/ESA/ASI Cassini spacecraft—would launch by 2031 on a Space Launch System or equivalent launch vehicle and utilize a Jupiter gravity assist for a 12 yr cruise to Neptune and a 4 yr prime orbital mission; alternatively a launch after 2031 would have a 16 yr direct-to-Neptune cruise phase. Our solution provides annual launch opportunities and allows for an easy upgrade to the shorter (12 yr) cruise. Odyssey would orbit Neptune retrograde (prograde with respect to Triton), using the moon's gravity to shape the orbital tour and allow coverage of Triton, Neptune, and the space environment. The atmospheric entry probe would descend in ∼37 minutes to the 10 bar pressure level in Neptune's atmosphere just before Odyssey's orbit-insertion engine burn. Odyssey's mission would end by conducting a Cassini-like “Grand Finale,” passing inside the rings and ultimately taking a final great plunge into Neptune's atmosphere.

The Alice ultraviolet spectrograph on board the \textit{Rosetta} orbiter provided the first near-nucleus ultraviolet observations of a cometary coma from arrival at comet 67P/Churyumov-Gerasimenko in 2014 August through 2016 September. The characterization of atomic and molecular emissions in the coma revealed the unexpected contribution of dissociative electron impact emission at large heliocentric distances and during some outbursts. This mechanism also proved useful for compositional analysis, and Alice observed many cases that suggested elevated levels of the supervolatile \ce{O2}, identifiable in part to their emissions resulting from dissociative electron impact. In this paper we present the first two-dimensional UV maps constructed from Alice observations of atomic emission from 67P during an increase in cometary activity on 2015 November 7-8. Comparisons to observations of background coma and of an earlier collimated jet are used to describe possible changes to the near-nucleus coma and plasma. To verify the mapping method and place the Alice observations in context, comparisons to images derived from the MIRO and VIRTIS-H instruments are made. The spectra and maps we present show an increase in dissociative electron impact emission and an \ce{O2}/\ce{H2O} ratio of $\sim$0.3 for the activity; these characteristics have been previously identified with cometary outbursts seen in Alice data. Further, UV maps following the increases in activity show the spatial extent and emission variation experienced by the near-nucleus coma, informing future UV observations of comets that lack the same spatial resolution., Comment: 22 pages, 14 figures, 2 tables

We present the results of a molecular survey of comet 46P/Wirtanen undertaken with the IRAM 30-m and NOEMA radio telescopes in December 2018. Observations at IRAM 30-m during the 12-18 Dec. period comprise a 2 mm spectral survey covering 25 GHz and a 1 mm survey covering 62 GHz. The gas outflow velocity and kinetic temperature have been accurately constrained by the observations. We derive abundances of 11 molecules, some being identified remotely for the first time in a Jupiter-family comet, including complex organic molecules such as formamide, ethylene glycol, acetaldehyde, or ethanol. Sensitive upper limits on the abundances of 24 other molecules are obtained. The comet is found to be relatively rich in methanol (3.4 percent relative to water), but relatively depleted in CO, CS, HNC, HNCO, and HCOOH., Comment: 35 pages, 16 figures, to be published in Astronomy & Astrophysics

The Ultraviolet and Visible Spectrometer channel of the Mercury Atmospheric and Surface Composition Spectrometer instrument aboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft made near-daily observations of solar-scattered resonant emission from magnesium in Mercury's exosphere during the mission's orbital phase (March 2011–April 2015, ∼17 Mercury years). In this paper, a subset of these data (March 2013–April 2015) is described and analyzed to illustrate Mg's spatial and temporal variations. Dayside altitude profiles of emission are used to make estimates of the Mg density and temperature. The main characteristics of the Mg exosphere are (a) a predominant enhancement of emission in the morning (6 am–10 am) near perihelion, (b) a bulk temperature of ∼6000 K, consistent with impact vaporization as the predominant ejection process, (c) a near-surface density that varies from 5 cm −3 to 50 cm −3 and (d) a production rate that is strongest in the morning on the inbound leg of Mercury's orbit with rates ranging from 1 × 10 5 cm −2 s −1 to 8 × 10 5 cm −2 s −1 .

A systematic analysis of the mixing ratios with respect to H 2 O for eight species (CH 3 OH, HCN, NH 3 , H 2 CO, C 2 H 2 , C 2 H 6 , CH 4 , and CO) measured with high-resolution infrared spectroscopy in thirty comets between 1997 and 2013 is presented. Some trends are beginning to emerge when mixing ratios in individual comets are compared to average mixing ratios obtained for all species within the population. The variation in mixing ratios for all measured species is at least an order of magnitude. Overall, Jupiter-family comets are depleted in volatile species with respect to H 2 O compared to long-period Oort cloud comets, with the most volatile species showing the greatest relative depletion. There is a high positive correlation between the mixing ratios of HCN, C 2 H 6 , and CH 4 , whereas NH 3 , H 2 CO, and C 2 H 2 are moderately correlated with each other but generally uncorrelated or show only weak correlation with other species. CO is generally uncorrelated with the other measured species possibly because it has the highest volatility and is therefore more susceptible to thermal evolutionary effects. Most of these correlations appear to be independent of dynamical class with a few possible exceptions. Molecular mixing ratios for CH 3 OH, HCN, C 2 H 6 , and CH 4 show an expected behavior with heliocentric distance suggesting a dominant ice source, whereas there is emerging evidence that the mixing ratios of NH 3 , H 2 CO, C 2 H 2 , NH 2 , and CN may increase at small heliocentric distances, suggesting the possibility of additional sources related to the thermal decomposition of organic dust. Although this provides information on the composition of the most volatile grains in comets, it presents an additional difficulty in classifying comet chemistry because most comets within this dataset were only observed over a limited range of heliocentric distance. Although there is remarkable compositional diversity resulting in a unique chemical fingerprint for each comet, a hierarchical tree cluster analysis is used to determine a taxonomic classification system containing four groups and eleven subgroups. Optical and infrared comparisons indicate that mixing ratios of daughter species and potential parents from cometary ices are sometimes but not always consistent with one another. This suggests that in many comets there are significant sources of C 2 and/or CN from grains, and that the importance of these sources is variable within the comet population.

The 2018 perihelion passage of comet 46P/Wirtanen afforded an opportunity to measure the abundances and spatial distributions of coma volatiles in a Jupiter-family comet with exceptional spatial resolution for several weeks surrounding its closest approach to Earth (Δmin ∼0.078 au on UT December 16). We conducted near-infrared spectroscopic observations of 46P/Wirtanen using iSHELL at the NASA Infrared Telescope Facility on UT 2018 December 18 in direct coordination with observations using the newly upgraded NIRSPEC-2 instrument at the W. M. Keck Observatory, and securely detected fluorescent emission from CH3OH, C2H6, and H2O. This coordinated campaign utilizing the two premier near-infrared facilities in the northern hemisphere enabled us to sample distinct projections of the coma into the plane of the sky simultaneously, and provided an unprecedented view into the inner coma of 46P/Wirtanen near closest approach. We report rotational temperatures, production rates, and abundance ratios (i.e., mixing ratios) for all sampled species and compare our iSHELL results to simultaneous (or near-simultaneous) measurements taken with NIRSPEC-2. We demonstrate the extraordinary synergy of coordinated measurements using iSHELL and NIRSPEC-2, and advocate for future cometary studies that jointly leverage the capabilities of these two facilities.

A major upgrade to the NIRSPEC instrument at the Keck II telescope was successfully completed in time for near-infrared spectroscopic observations of comet 46P/Wirtanen during its exceptionally close flyby of Earth in 2018 December. These studies determined the abundances of several volatiles, including C2H2, C2H6, CH3OH, NH3, HCN, H2CO, and H2O. Long-slit spatial distributions of gas rotational temperature and column density are diagnostic for the presence of icy grains in the coma and understanding if different volatiles are associated with common or distinct outgassing sources. These spatial distributions suggest that C2H2, C2H6, and HCN have a common outgassing source, whereas H2O and CH3OH have additional, more extended sources. The synergy of these findings with observations by space missions (Rosetta and EPOXI) motivates continuing studies to address whether or not C2H6, C2H2, and HCN have a common source of release (plausibly associated with CO2) in a larger sample of comets and whether systematic differences exist in the release of these species compared to H2O and CH3OH. Abundances of volatiles are reported relative to H2O, as traditionally done, as well as C2H6. While not unique, the choice of C2H6 demonstrates the value of extending the chemical taxonomy of parent volatiles in comets toward additional compositional “baselines” and, importantly, closer integration between coma abundances and the underlying volatile associations as revealed by spatial distributions. Our findings on composition and sources of outgassing include information relevant to future evaluations of 46P/Wirtanen as a prospective spacecraft target.

The Alice ultraviolet spectrograph on the European Space Agency Rosetta spacecraft observed comet 67P/Churyumov-Gerasimenko in its orbit around the Sun for just over two years. Alice observations taken in 2015 October, two months after perihelion, show large increases in the comet's Ly-$\beta$, O I 1304, O I 1356, and C I 1657 $\AA$ atomic emission that initially appeared to indicate gaseous outbursts. However, the Rosetta Plasma Consortium instruments showed a coronal mass ejection (CME) impact at the comet coincident with the emission increases, suggesting that the CME impact may have been the cause of the increased emission. The presence of the semi-forbidden O I 1356 $\AA$ emission multiplet is indicative of a substantial increase in dissociative electron impact emission from the coma, suggesting a change in the electron population during the CME impact. The increase in dissociative electron impact could be a result of the interaction between the CME and the coma of 67P or an outburst coincident with the arrival of the CME. The observed dissociative electron impact emission during this period is used to characterize the O2 content of the coma at two peaks during the CME arrival. The mechanism that could cause the relationship between the CME and UV emission brightness is not well constrained, but we present several hypotheses to explain the correlation., Comment: 11 pages, 7 figures, 3 tables

The Alice far-ultraviolet imaging spectrograph onboard Rosetta observed emissions from atomic and molecular species from within the coma of comet 67P/Churyumov-Gerasimenko during the entire escort phase of the mission from 2014 August to 2016 September. The initial observations showed that emissions of atomic hydrogen and oxygen close to the surface were produced by energetic electron impact dissociation of H2O. Following delivery of the lander, Philae, on 2014 November 12, the trajectory of Rosetta shifted to near-terminator orbits that allowed for these emissions to be observed against the shadowed nucleus that, together with the compositional heterogeneity, enabled us to identify unique spectral signatures of dissociative electron impact excitation of H2O, CO2, and O2. CO emissions were found to be due to both electron and photoexcitation processes. Thus we are able, from far-ultraviolet spectroscopy, to qualitatively study the evolution of the primary molecular constituents of the gaseous coma from start to finish of the escort phase. Our results show asymmetric outgassing of H2O and CO2 about perihelion, H2O dominant before and CO2 dominant after, consistent with the results from both the in situ and other remote sensing instruments on Rosetta., 11 pages, 8 figures, accepted for publication in the Astronomical Journal

High-resolution infrared spectra of Jupiter-family comet 45P/Honda-Mrkos-Pajdusakova were obtained with NIRSPEC at the W. M. Keck Observatory on two post-perihelion dates (UT 2017 February 13 and 19), when the comet was at heliocentric distances of 1.01 and 1.10 AU, respectively. On UT February 13, H2O was measured simultaneously with six trace parent molecules: CH3OH, C2H6, HCN, NH3, C2H2, and H2CO. On UT February 19, CH4 and CO were also targeted in addition to the species measured on UT February 13. Abundances of CO, CH4, and C2H2 relative to H2O are consistent with values obtained from IRTF/iSHELL observations of 45P in early January 2017 just after perihelion when the heliocentric distance was 0.55–0.56 AU. Differences are seen in H2CO/H2O, C2H6/H2O, CH3OH/H2O, and HCN/H2O in February compared to January. Additionally, NH3 abundances appear highly variable during the February measurements, suggesting possible fluctuations of a factor of ten; however, there is significant uncertainty in quantifying NH3 owing to the marginal detections of only one or two lines on each of the two dates. Combining all infrared spectroscopic observations of 45P in January and February 2017, a post-perihelion relationship of Q(H2O) = (2.81 ± 0.25) × 1027 [Rh(−3.83±0.18)] molecules s−1 is derived. However, all measurements suggest significant variability in H2O production on timescales of hours and days. Compared to other comets, volatile abundances relative to H2O in 45P are as follows: CO (depleted relative to all measured comets), CH3OH (enriched/all comets), CH4 and C2H6 (typical/all comets, enriched/Jupiter-family comets), C2H2 (depleted/all comets, typical/Jupiter-family comets), H2CO (January: typical, February depleted/all comets), HCN (January: severely depleted, February: typical/Jupiter-family comets). The small geocentric distances of the comet in February 2017 provide high spatial resolution in the coma of 45P (~12 and 19 km/pixel on February 13 and 19, respectively). Overall, the spatial distributions of volatiles and dust suggest a relatively symmetric and uniform coma during the UT February 13 and 19 observations, with small spatial differences noted between some volatile species. Measured C2H2 and HCN abundances are consistent with HCN as the primary parent of CN and C2H2 as a significant but not primary parent for C2, based on C2 and CN production rate measurements from the 2017 and previous apparitions. Extracted spectra show an increase in the dust-to-gas ratio in 45P from February 13 to 19 in agreement with contemporaneous narrowband optical measurements.

Comet C/2016 R2 (PanSTARRS) has a peculiar volatile composition, with CO being the dominant volatile as opposed to H$_2$O and one of the largest N$_2$/CO ratios ever observed in a comet. Using observations obtained with the \textit{Spitzer Space Telescope}, NASA's Infrared Telescope Facility, the 3.5-meter ARC telescope at Apache Point Observatory, the Discovery Channel Telescope at Lowell Observatory, and the Arizona Radio Observatory 10-m Submillimeter Telescope we quantified the abundances of 12 different species in the coma of R2 PanSTARRS. We confirm the high abundances of CO and N$_2$ and heavy depletions of H$_2$O, HCN, CH$_3$OH, and H$_2$CO compared to CO reported by previous studies. We provide the first measurements (or most sensitive measurements/constraints) on H$_2$O, CO$_2$, CH$_4$, C$_2$H$_6$, OCS, C$_2$H$_2$, and NH$_3$, all of which are depleted relative to CO by at least one to two orders of magnitude compared to values commonly observed in comets. The observed species also show strong enhancements relative to H$_2$O, and even when compared to other species like CH$_4$ or CH$_3$OH most species show deviations from typical comets by at least a factor of two to three. The only mixing ratios found to be close to typical are CH$_3$OH/CO$_2$ and CH$_3$OH/CH$_4$. While R2 PanSTARRS was located at a heliocentric distance of 2.8 AU at the time of our observations in January/February 2018, we argue that this alone cannot account for the peculiar observed composition of this comet and therefore must reflect its intrinsic composition. We discuss possible implications for this clear outlier in compositional studies of comets obtained to date, and encourage future dynamical and chemical modeling in order to better understand what the composition of R2 PanSTARRS tells us about the early Solar System., 36 pages, 12 figures, 7 tables, accepted for publication in AJ

We present observations of the binary near-Earth Asteroid (175706) 1996 FG3 in the 2–4 μm spectral region, obtained on multiple nights using the SpeX instrument on the NASA Infrared Telescope Facility (IRTF). We find evidence for an absorption band of ∼5–10% (depending on the night and details of continuum choice), diagnostic for hydrated/hydroxylated minerals on the asteroid surface. This demonstrates that the optical surface of 1996 FG3 has not been heated to dehydrating temperatures. Sample-return missions targeting 1996 FG3 will likely find relatively fresh areas for sampling.

For most of the orbital phase of the MESSENGER mission, a regular search for weakly emitting or less abundant species in Mercury's exosphere resulted in non-detections. However, during the final Earth year of the mission, emission from multiple lines of manganese, aluminum, and ionized calcium was detected. These observations validate the detection of a single line of ionized calcium during the third MESSENGER Mercury flyby, provide definitive confirmation for weak aluminum detections in ground-based observations, and represent the discovery of manganese in Mercury's exosphere. These detections occurred over a limited range of pre-dawn local times and Mercury true anomaly angles (0o-70o), and each has a distinct spatial distribution. Equally interesting is the absence of detectable emission from oxygen at limits well below the levels reported for Mariner 10.

The Ultraviolet and Visible Spectrometer (UVVS) component of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MESSENGER spacecraft characterized the local-time distribution of the sodium exosphere over the course of its orbital mission. The observations show that the sodium exosphere is enhanced above Mercury's cold-pole longitudes. Based on previously published sodium exosphere models we infer that these regions act as nightside surface reservoirs, temporary sinks to the exosphere that collect sodium atoms transported anti-sunward. The reservoirs are revealed as exospheric enhancements when they are exposed to sunlight. As in the models the reservoir is depleted as the cold poles rotate from dawn to dusk, but unlike the models the depletion is only partial. The persistence of the reservoir means that it could, over the course of geologically long periods of time, contribute to an increase in the bulk concentration of sodium near the cold-pole longitudes.

We obtained high-resolution (lambda divided by delta times lambda equals approximately 25,000) pre-perihelion spectra of Comet C/2013 V5 (Oukaimeden) using NIRSPEC at Keck II on UT 2014 September 5-6, and CSHELL (Cryogenic Echelle Spectrograph) at the NASA-Infrared Telescope Facility on September 11-13, altogether spanning a range in heliocentric distance R (sub h) equals 0.789-0.698 astronomical units. We report water production rates, and production rates and abundance ratios relative to co-measured H2O for eight trace molecules: CO, H2CO, CH3OH, CH4, C2H2, C2H6, HCN, and NH3. Our measured water production rates from NIRSPEC ( Near Infra-Red Spectrograph) and CSHELL observations remained relatively constant and were close to those from SOHO (Solar and Heliospheric Observatory) / Solar Wind Anisotropies observations that encompassed our dates, suggesting H2O production dominated by release directly from or within approximately 2000 kilometers of the nucleus. All trace volatiles were depleted relative to their respective median abundances among comets, excepting NH3, which was consistent with its median abundance. Most surprising were pronounced increases in abundance ratios for CH3OH (by 51 percent relative to simultaneously measured H2O) and especially C2H6 (by 87 percent) between September 5 and 6. On September 5, C2H6 was severely depleted, consistent with its lowest abundance yet measured for any comet. It also tracked the spatial profile of H2O, suggesting C2H6 was associated with a polar ice phase dominating gas production. On September 6, C2H6 was only moderately depleted and was spatially distinct from H2O, suggesting both polar- and nonpolar-dominated ice phases contributed to the activity then. Our results are consistent with a nonhomogeneous volatile composition for C/2013V5, implying differential processing of its constituent ices.

The highly favorable 2017 apparition of 2P/Encke allowed the first comprehensive comparison of primary volatile abundances in a given comet across multiple apparitions. This apparition offered opportunities to address pressing questions in cometary science, including investigating evolutionary and/or heliocentric distance (R(sub h)) effects on volatile production, sampling the hypervolatiles CO and CH4 in an ecliptic comet, and measuring volatile release at small R(sub h). The faintness and frequently low geocentric velocity of ecliptic comets during most apparitions make our near-infrared observations of these hypervolatiles rare and of high scientific impact. We characterized the volatile composition of 2P/Encke on three post-perihelion dates using the iSHELL spectrograph at the NASA Infrared Telescope Facility on Maunakea, HI. We detected fluorescent emission from nine primary volatiles (H2O, CO, C2H6, CH3OH, CH4, H2CO, NH3, OCS, and HCN) and three fragment species (OH*, NH2, and CN), and obtained a sensitive upper limit for C2H2. We report rotational temperatures, production rates, and mixing ratios (abundances relative to H2O). Compared to mean abundances in comets observed to date in the near-infrared, mixing ratios of trace gases in 2P/Encke were depleted for all species except H2CO and NH3, which were “normal.” The detection of the hypervolatiles CO and CH4 is particularly notable given the paucity of measurements in ecliptic comets. We observed significant differences in primary volatile composition compared to published pre-perihelion results from 2003 at larger R(sub h). We discuss possible mechanisms for these differences and discuss these results in the context of findings from the Rosetta mission and ground-based studies of comets.

We report production rates for H2O and eight trace molecules (CO, C_2H_6, CH_4, CH_3OH, NH_3, H_2CO, HCN, C_2H_2) in the dynamically new, Sun-grazing Comet C/2012 S1 (ISON), using high-resolution spectroscopy at Keck II and the NASA IRTF on 10 pre-perihelion dates encompassing heliocentric distances R_h = 1.21–0.34 AU. Measured water production rates spanned two orders of magnitude, consistent with a long-term heliocentric power law Q(H_2O) ∝ R_h^(-3.1±0.1). Abundance ratios for CO, C_2H_6, and CH_4 with respect to H_2O remained constant with R_h and below their corresponding mean values measured among a dominant sample of Oort Cloud comets. CH_3OH was also depleted for R_h > 0.5 AU, but was closer to its mean value for R_h ≤ 0.5 AU. The remaining four molecules exhibited higher abundance ratios within 0.5 AU: for R_h > 0.8 AU, NH_3 and C_2H_2 were consistent with their mean values while H_2CO and HCN were depleted. For R_h < 0.5 AU, all four were enriched, with NH_3, H_2CO, and HCN increasing most. Spatial profiles of gas emission in ISON consistently peaked sunward of the dust continuum, which was asymmetric antisunward and remained singly peaked for all observations. NH_3 within 0.5 AU showed a broad spatial distribution, possibly indicating its release in the coma provided that optical depth effects were unimportant. The column abundance ratio NH_2/H_2O at 0.83 AU was close to the "typical" NH/OH from optical wavelengths, but was higher within 0.5 AU. Establishing its production rate and testing its parentage (e.g., NH_3) require modeling of coma outflow.

Volatile production rates, relative abundances, rotational temperatures, and spatial distributions in the coma were measured in C/2012 S1 (ISON) using long-slit high-dispersion ( λ /Δ λ ∼ 2.5 × 10 4 ) infrared spectroscopy as part of a worldwide observing campaign. Spectra were obtained on UT 2013 October 26 and 28 with NIRSPEC at the W.M. Keck Observatory, and UT 2013 November 19 and 20 with CSHELL at the NASA IRTF. H 2 O was detected on all dates, with production rates increasing markedly from (8.7 ± 1.5) × 10 27 molecules s −1 on October 26 ( R h = 1.12 AU) to (3.7 ± 0.4) × 10 29 molecules s −1 on November 20 ( R h = 0.43 AU). Short-term variability of H 2 O production is also seen as observations on November 19 show an increase in H 2 O production rate of nearly a factor of two over a period of about 6 h. C 2 H 6 , CH 3 OH and CH 4 abundances in ISON are slightly depleted relative to H 2 O when compared to mean values for comets measured at infrared wavelengths. On the November dates, C 2 H 2 , HCN and OCS abundances relative to H 2 O appear to be within the range of mean values, whereas H 2 CO and NH 3 were significantly enhanced. There is evidence that the abundances with respect to H 2 O increased for some species but not others between October 28 ( R h = 1.07 AU) and November 19 ( R h = 0.46 AU). The high mixing ratios of H 2 CO/CH 3 OH and C 2 H 2 /C 2 H 6 on November 19, and changes in the mixing ratios of some species with respect to H 2 O between October 28 to November 19, indicates compositional changes that may be the result of a transition from sampling radiation-processed outer layers in this dynamically new comet to sampling more pristine natal material as the outer processed layer was increasingly eroded and the thermal wave propagated into the nucleus as the comet approached perihelion for the first time. On November 19 and 20, the spatial distribution for dust appears asymmetric and enhanced in the antisolar direction, whereas spatial distributions for volatiles (excepting CN) appear symmetric with their peaks slightly offset in the sunward direction compared to the dust. Spatial distributions for H 2 O, HCN, C 2 H 6 , C 2 H 2 , and H 2 CO on November 19 show no definitive evidence for significant contributions from extended sources; however, broader spatial distributions for NH 3 and OCS may be consistent with extended sources for these species. Abundances of HCN and C 2 H 2 on November 19 and 20 are insufficient to account for reported abundances of CN and C 2 in ISON near this time. Differences in HCN and CN spatial distributions are also consistent with HCN as only a minor source of CN in ISON on November 19 as the spatial distribution of CN in the coma suggests a dominant distributed source that is correlated with dust and not volatile release. The spatial distributions for NH 3 and NH 2 are similar, suggesting that NH 3 is the primary source of NH 2 with no evidence of a significant dust source of NH 2 ; however, the higher production rates derived for NH 3 compared to NH 2 on November 19 and 20 remain unexplained. This suggests a more complete analysis that treats NH 2 as a distributed source and accounts for its emission mechanism is needed for future work.

Here we explore a technique for constraining physical properties of near-Earth asteroids (NEAs) based on variability in thermal emission as a function of viewing aspect. We present case studies of the low albedo, near-Earth asteroids (285263) 1998 QE2 and (175706) 1996 FG3. The Near-Earth Asteroid Thermal Model (NEATM) is used to fit signatures of thermal emission in near-infrared (0.8 - 2.5 micron) spectral data. This analysis represents a systematic study of thermal variability in the near-IR as a function of phase angle. The observations of QE2 imply that carefully timed observations from multiple viewing geometries can be used to constrain physical properties like retrograde versus prograde pole orientation and thermal inertia. The FG3 results are more ambiguous with detected thermal variability possibly due to systematic issues with NEATM, an unexpected prograde rotation state, or a surface that is spectrally and thermally heterogenous. This study highlights the potential diagnostic importance of high phase angle thermal measurements on both sides of opposition. We find that the NEATM thermal beaming parameters derived from our near-IR data tend to be of order 10's of percent higher than parameters from ensemble analyses of longer wavelength data sets. However, a systematic comparison of NEATM applied to data in different wavelength regimes is needed to understand whether this offset is simply a reflection of small number statistics or an intrinsic limitation of NEATM when applied to near-IR data. With the small sample presented here, it remains unclear whether NEATM modeling at near-IR wavelengths can robustly determine physical properties like pole orientation and thermal inertia., Comment: Accepted to Icarus

We used the new high spectral resolution cross-dispersed facility spectrograph, iSHELL, at the NASA Infrared Telescope Facility on Maunakea, HI, to observe Jupiter-family comet (JFC) 45P/Honda-Mrkos-Pajdusakova. We report water production rates, as well as production rates and abundance ratios relative to H2O, for eight trace parent molecules (native ices), CO, CH4, H2CO, CH3OH, HCN, NH3, C2H2, and C2H6, on 2 days spanning UT 2017 January 6/7 and 7/8, shortly following perihelion. Trace species were measured simultaneously with H2O and/or OH prompt emission, a proxy for H2O production, thereby providing a robust and consistent means of establishing the native ice composition of 45P. Its favorable geocentric radial velocity (approximately minus 35 kilometers per second) permitted sensitive measures of the "hypervolatiles" CO and CH4, which are substantially undercharacterized in JFCs. Our results represent the most precise ground-based measures of CO and CH4 to date in a JFC, providing a foundation for building meaningful statistics regarding their abundances. The abundance ratio for CH4 in 45P (0.79 percent plus or minus 0.06 percent relative to H2O) was consistent with its median value as measured among Oort Cloud comets, whereas CO (0.60 percent plus or minus 0.04 percent) was strongly depleted. Compared with all measured comets, HCN (0.049 percent plus or minus 0.012 percent) was strongly depleted, CH3OH (3.6 percent plus or minus 0.3 percent) was enriched, and the remaining species were consistent with their respective median abundances. The volatile composition measured for 45P could indicate processing of ices prior to their incorporation into its nucleus. Spatial analysis of emissions suggests enhanced release of more volatile species into the sunward-facing hemisphere of the coma.

Volatile abundances in Jupiter-family Comet 81P/Wild 2 were measured on four dates in February and March 2010 using high-dispersion ( λ Δ λ ∼ 2.5 × 10 4 ) infrared spectroscopy with NIRSPEC at the W.M. Keck Observatory. H 2 O was detected on all dates, including measurements on UT March 29 of lines from the ν 2 + ν 3 − ν 2 hot-band not previously targeted in comets. C 2 H 6 and HCN were detected on three dates, and CH 3 OH was detected on one date. Tentative detections or upper-limits are reported for CH 3 OH on other dates, as well as for C 2 H 2 , H 2 CO, and NH 3 . Abundances of all species relative to H 2 O are in the typical range with the exception of CH 3 OH, which is depleted compared to other comets. Gas production was significantly higher in late February than in late March. Rotational temperatures were determined for H 2 O on UT February 22 and 23 and found to be about 30–40 K. The spatial distributions of H 2 O, C 2 H 6 , and CH 3 OH are all symmetric and similar to the spatial distribution of the dust continuum. H 2 O abundances from this work are compared to other measurements from both the 1997 and 2010 apparitions. There is no clear evidence of a change in overall gas productivity between the two apparitions within measurement accuracy. Abundances of C 2 H 2 , C 2 H 6 , HCN and NH 3 are consistent with these species being the primary parents of C 2 , CN, NH and NH 2 as measured at optical wavelengths. Although optically classified as carbon-chain depleted, Wild 2 appears more chemically similar in parent volatile chemistry to carbon-chain typical comets; however, we note that in the small sample of Jupiter-family comets measured to date, each comet is chemically distinct.

We performed high-dispersion near-infrared spectroscopic observations of comet C/2010 G2 (Hill) at 2.5 AU from the Sun using NIRSPEC (R ≈ 25,000) at the Keck II Telescope on UT 2012 January 9 and 10, about a week after an outburst had occurred. Over the two nights of our observations, prominent emission lines of CH{sub 4} and C{sub 2}H{sub 6}, along with weaker emission lines of H{sub 2}O, HCN, CH{sub 3}OH, and CO were detected. The gas production rate of CO was comparable to that of H{sub 2}O during the outburst. The mixing ratios of CO, HCN, CH{sub 4}, C{sub 2}H{sub 6}, and CH{sub 3}OH with respect to H{sub 2}O were higher than those for normal comets by a factor of five or more. The enrichment of CO and CH{sub 4} in comet Hill suggests that the sublimation of these hypervolatiles sustained the outburst of the comet. Some fraction of water in the inner coma might exist as icy grains that were likely ejected from nucleus by the sublimation of hypervolatiles. Mixing ratios of volatiles in comet Hill are indicative of the interstellar heritage without significant alteration in the solar nebula.

We conducted high-dispersion spectroscopic observations of Comet 103P/Hartley 2 in the near-infrared wavelength region using the Keck II telescope with NIRSPEC. We obtained observations on four dates, with the last observations performed during the EPOXI closest approach. For this work we focus on the observations performed on UT 2010 October 17 and 21, while observations carried out on UT 2010 September 16 and November 4 have been reported elsewhere. On all dates the spatial distributions in the coma of C 2 H 6 , HCN and C 2 H 2 were similar to each other and consistent with the CN-jet morphology observed from optical observations. The spatial distributions in the coma of H 2 O and CH 3 OH were also similar to each other, but were generally different from C 2 H 6 , HCN and C 2 H 2 . There might be two distinct phases of ice in Comet Hartley 2; one is enriched in H 2 O and CH 3 OH, and another is enriched in more volatile species (C 2 H 6 , C 2 H 2 , and HCN). It is possible that highly volatile species like C 2 H 6 were segregated from the H 2 O matrix when warmer conditions were prevalent. We summarize our spectroscopic observations and report absolute production rates and mixing ratios of parent volatiles. There was no evidence of any significant diversity in the mixing ratios of parent volatiles on different dates. Comet Hartley 2 was normal in CH 3 OH/H 2 O, C 2 H 6 /H 2 O, C 2 H 2 /H 2 O, NH 3 /H 2 O but depleted in H 2 CO/H 2 O and CH 4 /H 2 O. OPRs of H 2 O in Comet Hartley 2 measured in its 2010 apparition were consistent with those observed by the Infrared Satellite Observatory in 1997.

We obtained high-resolution (λ/Δλ ∼ 28,000) infrared spectra of Comet 103P/Hartley 2 on UT 2010 November 4.6 using the NIRSPEC spectrometer at the W.M. Keck Observatory. Here we present spectra of Hartley 2 between 2.832 and 3.639 μm (3531–2748 cm−1), representing the most complete high-resolution infrared survey of a Jupiter-family comet to date in this wavelength region. We have tabulated rest frequencies, line fluxes, line signal-to-noise ratios and line widths for all detected emissions. Fluorescence models, published line lists and laboratory spectra were used to obtain molecular assignments for detected emissions. Multiple lines of the following species were detected in Hartley 2: H2O, OH, CH3OH, C2H6, HCN, C2H2, H2CO, NH3 and NH2. All identified species seen in this survey have been previously detected in comets. There were 364 distinct emission features present in these spectra, of which 36 were unidentified. We compare the spectrum of Hartley 2 to chemically different Jupiter-family Comets 73P/Schwassmann–Wachmann 3-B and 17P/Holmes in order to obtain additional information on the characteristics of unknown lines through the comparison of relative line fluxes for corresponding emissions in these comets. For the strongest unidentified emissions, additional information was also obtained through a comparison of their spatial distributions in the coma to that of known emission features in Hartley 2. This spectral survey of Hartley 2 provides detailed information about its overall volatile chemistry, provides a comparison to past and future high-resolution infrared datasets, and further characterizes the most promising spectral regions for future molecular searches in comets.

The Jupiter-family comet 10P/Tempel 2 was observed during its 2010 return with the Herschel Space Observatory. We present here the observation of the (J, K) = (1, 0)-(0, 0) transition of ammonia at 572 GHz in this comet with the Heterodyne Instrument for the Far Infrared (HIFI) of Herschel. We also report on radio observations of other molecules (HCN, CH3OH, H2S and CS) obtained during the 1999 return of the comet with the CSO telescope and the JCMT, and during its 2010 return with the IRAM 30-m telescope. Molecular abundances relative to water are 0.09%, 1.8%, 0.4%, and 0.08% for HCN, CH3OH, H2S, and CS, respectively. An abundance of 0.5% for NH3 is obtained, which is similar to the values measured in other comets. The hyperfine structure of the ammonia line is resolved for the first time in an astronomical source. Strong anisotropy in the outgassing is present in all observations from 1999 to 2010 and is modelled to derive the production rates., 6 pages and 8 figures. Accepted for publication in Astronomy & Astrophysics

Earth- and space-based observations provide synergistic information for space mission encounters by providing data over longer timescales, at different wavelengths and using techniques that are impossible with an in situ flyby. We report here such observations in support of the EPOXI spacecraft flyby of comet 103P/Hartley 2. The nucleus is small and dark, and exhibited a very rapidly changing rotation period. Prior to the onset of activity, the period was ∼16.4 hr. Starting in 2010 August the period changed from 16.6 hr to near 19 hr in December. With respect to dust composition, most volatiles and carbon and nitrogen isotope ratios, the comet is similar to other Jupiter-family comets. What is unusual is the dominance of CO2-driven activity near perihelion, which likely persists out to aphelion. Near perihelion the comet nucleus was surrounded by a large halo of water-ice grains that contributed significantly to the total water production. Fil: Meech, K. J.. Institute for Astronomy; Estados Unidos Fil: A’Hearn, M. F.. University of Maryland; Estados Unidos Fil: Adams, J. A.. Cornell University; Estados Unidos Fil: Bacci, P.. Centro Astronomico di Libbiano; Italia Fil: Bai, J.. Chinese Academy of Sciences; China Fil: Barrera, L.. Universidad Metropolitana de Ciencias de la Educacion; Chile Fil: Battelino, M.. Swedish Space Corporation; Suecia Fil: Bauer, J. M.. Jet Propulsion Laboratory; Estados Unidos Fil: Becklin, E.. Stratospheric Observatory for Infrared Astronomy; Estados Unidos Fil: Bhatt, B.. Indian Institute of Astrophysics; India Fil: Biver, N.. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia Fil: Bockelee Morvan, D.. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia Fil: Bodewits, D.. University of Maryland; Estados Unidos Fil: Bohnhardt, H.. Gobierno de la Republica Federal de Alemania. Max Planck Institut Fur Astrophysik; Alemania Fil: Boissier, J.. Inst. di Radioastronomia; Italia Fil: Bonev, B. P.. Catholic University of America; Estados Unidos Fil: Borghini, W.. Osservatorio Astronomico Naturalistico di Casasco; Italia Fil: Brucato, J. R.. Osservatorio Astrofisico di Arcetri; Italia Fil: Bryssinck, E.. Brixiis Observatory; Bélgica Fil: Buie. M. W.. Southwest Research Institute; Estados Unidos Fil: Canovas, H.. Utrecht University; Países Bajos Fil: Castellano, D.. Unione Astrofili Italiani; Italia Fil: Charnley, S. B.. National Aeronautics And Space Administration; Estados Unidos Fil: Chen, W. P.. National Taiwan Normal University; Corea del Sur Fil: Chiang, P.. Korea Astronomy and Space Science Institute; Corea del Sur Fil: Choi, Y. J.. Korea Astronomy and Space Science Institute; Corea del Sur Fil: Christian, D. J.. California State University; Estados Unidos Fil: Chuang, Y. L.. National Taiwan Normal University; Corea del Sur Fil: Cochran, A. L.. University of Texas; Estados Unidos Fil: Melita, Mario Daniel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina