Infrared Telescope Facility Research Articles

New Observations and Modeling of Jupiter's Quasi‐Quadrennial Oscillation

AbstractThe quasi‐quadrennial oscillation (QQO) and its ∼4 year period in Jupiter's atmosphere were first discovered in 7.8 μm infrared observations spanning the 1980s and 1990s from detecting semiregular variations in equatorial brightness temperatures near 10 hPa. New observations that probe between 0.1 and 30 hPa in Jupiter's atmosphere using the Texas Echelon Cross Echelle Spectrograph (TEXES), mounted on the NASA Infrared Telescope Facility, have characterized the vertical structure of the QQO during a complete cycle between January 2012 and April 2016. These new observations show the thermal oscillation previously detected at 10 hPa and that it extends over a pressure range of 2–17 hPa. We have incorporated a spectrum of wave drag parameterizations into the Explicit Planetary Isentropic Code general circulation model to simulate the observed Jovian QQO temperature signatures inferred from the TEXES observations as a function of latitude. A new stochastic wave drag parameterization explores vertical wind structure and offers insight into the spectra of waves that likely exist in Jupiter's atmosphere to force the QQO. High‐frequency gravity waves produced from convection likely contribute significantly to the QQO momentum budget. The model temperature outputs show strong correlations to equatorial and surrounding latitude temperature fields retrieved from the TEXES data sets at different epochs. Our results reproduce the QQO phenomenon as a zonal jet that descends over time in response to Jovian atmospheric forcing (e.g., gravity waves from convection).

Composition of Jupiter irregular satellites sheds light on their origin

Irregular satellites of Jupiter with their highly eccentric, inclined and distant orbits suggest that their capture took place just before the giant planet migration. We aim to improve our understanding of the surface composition of irregular satellites of Jupiter to gain insight into a narrow time window when our Solar System was forming. We observed three Jovian irregular satellites, Himalia, Elara, and Carme, using a medium-resolution 0.8-5.5 micro m spectrograph on the National Aeronautics and Space Administration (NASA) Infrared Telescope Facility (IRTF). Using a linear spectral unmixing model we have constrained the major mineral phases on the surface of these three bodies. Our results confirm that the surface of Himalia, Elara, and Carme are dominated by opaque materials such as those seen in carbonaceous chondrite meteorites. Our spectral modeling of NIR spectra of Himalia and Elara confirm that their surface composition is the same and magnetite is the dominant mineral. A comparison of the spectral shape of Himalia with the two large main C-type asteroids, Themis (D 176 km) and Europa (D 352 km), suggests surface composition similar to Europa. The NIR spectrum of Carme exhibits blue slope up to 1.5 microm and is spectrally distinct from those of Himalia and Elara. Our model suggests that it is compositionally similar to amorphous carbon. Himalia and Elara are compositionally similar but differ significantly from Carme. These results support the hypotheses that the Jupiter irregular satellites are captured bodies that were subject to further breakup events and clustered as families based on their similar physical and surface compositions.

The quest for H$_3^+$ at Neptune: deep burn observations with NASA IRTF iSHELL

Emission from the molecular ion H$_3^+$ is a powerful diagnostic of the upper atmosphere of Jupiter, Saturn, and Uranus, but it remains undetected at Neptune. In search of this emission, we present near-infrared spectral observations of Neptune between 3.93 and 4.00 $\mu$m taken with the newly commissioned iSHELL instrument on the NASA Infrared Telescope Facility in Hawaii, obtained 17-20 August 2017. We spent 15.4 h integrating across the disk of the planet, yet were unable to unambiguously identify any H$_3^+$ line emissions. Assuming a temperature of 550 K, we derive an upper limit on the column integrated density of $1.0^{+1.2}_{-0.8}\times10^{13}$ m$^{-2}$, which is an improvement of 30\% on the best previous observational constraint. This result means that models are over-estimating the density by at least a factor of 5, highlighting the need for renewed modelling efforts. A potential solution is strong vertical mixing of polyatomic neutral species from Neptune's upper stratosphere to the thermosphere, reacting with H$_3^+$, thus greatly reducing the column integrated H$_3^+$ densities. This upper limit also provide constraints on future attempts at detecting H$_3^+$ using the James Webb Space Telescope.

Hypervolatiles in a Jupiter-family Comet: Observations of 45P/Honda–Mrkos–Pajdušáková Using iSHELL at the NASA-IRTF

Abstract 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–Pajdušáková. 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 −35 km s−1) 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% ± 0.06% relative to H2O) was consistent with its median value as measured among Oort Cloud comets, whereas CO (0.60% ± 0.04%) was strongly depleted. Compared with all measured comets, HCN (0.049% ± 0.012%) was strongly depleted, CH3OH (3.6% ± 0.3%) 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.

Spectral Variability of Two Rapidly Rotating Brown Dwarfs: 2MASS J08354256-0819237 and 2MASS J18212815+1414010

Abstract L dwarfs exhibit low-level, rotationally modulated photometric variability generally associated with heterogeneous, cloud-covered atmospheres. The spectral character of these variations yields insight into the particle sizes and vertical structure of the clouds. Here, we present the results of a high-precision, ground-based, near-infrared, spectral monitoring study of two mid-type L dwarfs that have variability reported in the literature, 2MASS J08354256−0819237 and 2MASS J18212815+1414010, using the SpeX instrument on the Infrared Telescope Facility. By simultaneously observing a nearby reference star, we achieve per-band sensitivity in relative brightness changes across the 0.9–2.4 μm bandwidth. We find that 2MASS J0835−0819 exhibits marginal (≲0.5% per band) variability with no clear spectral dependence, while 2MASS J1821+1414 varies by up to ±1.5% at 0.9 μm, with the variability amplitude declining toward longer wavelengths. The latter result extends the variability trend observed in prior HST/WFC3 spectral monitoring of 2MASS J1821+1414, and we show that the full 0.9–2.4 μm variability amplitude spectrum can be reproduced by Mie extinction from dust particles with a log-normal particle size distribution with a median radius of 0.24 μm. We do not detect statistically significant phase variations with wavelength. The different variability behavior of 2MASS J0835−0819 and 2MASS J1821+1414 suggests dependencies on viewing angle and/or overall cloud content, underlying factors that can be examined through a broader survey.

Jupiter’s auroral-related stratospheric heating and chemistry II: Analysis of IRTF-TEXES spectra measured in December 2014

We present a retrieval analysis of TEXES (Texas Echelon Cross Echelle Spectrograph (Lacy et al., 2002)) spectra of Jupiter’s high latitudes obtained on NASA’s Infrared Telescope Facility on December 10 and 11th 2014. The vertical temperature profile and vertical profiles of C2H2, C2H4 and C2H6 were retrieved at both high-northern and high-southern latitudes and results were compared in ‘quiescent’ regions and regions known to be affected by Jupiter’s aurora in order to highlight how auroral processes modify the thermal structure and hydrocarbon chemistry of the stratosphere. In qualitative agreement with Sinclair et al. (2017a), we find temperatures in auroral regions to be elevated with respect to quiescent regions at two discrete pressures levels at approximately 1 mbar and 0.01 mbar. For example, in comparing retrieved temperatures at 70°N, 60°W (a representative quiescent region) and 70°N, 180°W (centred on the northern auroral oval), temperatures increase by 19.0 ± 4.2 K at 0.98 mbar, 20.8 ± 3.9 K at 0.01 mbar but only by 8.3 ± 4.9 K at the intermediate level of 0.1 mbar. We conclude that elevated temperatures at 0.01 mbar result from heating by joule resistance of the atmosphere and the energy imparted by electron and ion precipitation. However, temperatures at 1 mbar are considered to result either from heating by shortwave radiation of aurorally-produced haze particulates or precipitation of higher energy population of charged particles. Our former conclusion would be consistent with results of auroral-chemistry models, that predict the highest number densities of aurorally-produced haze particles at this pressure level (Wong et al., 2000, 2003). C2H2 and C2H4 exhibit enrichments but C2H6 remains constant within uncertainty when comparing retrieved concentrations in the northern auroral region with quiescent longitudes in the same latitude band. At 1 mbar, C2H2 increases from 278.4 ± 40.3 ppbv at 70°N, 60°W to 564.4 ± 72.0 ppbv at 70°N, 180°W and at 0.01 mbar, over the same longitude range at 70°N, C2H4 increases from 0.669 ± 0.129 ppmv to 6.509 ± 0.811 ppmv. However, we note that non-LTE (local thermodynamic equilibrium) emission may affect the cores of the strongest C2H2 and C2H4 lines on the northern auroral region, which may be a possible source of error in our derived concentrations. We retrieved concentrations of C2H6 at 1 mbar of 9.03 ± 0.98 ppmv at 70°N, 60°W and 7.66 ± 0.70 ppmv at 70°N, 180°W. Thus, C2H6’s concentration appears constant (within uncertainty) as a function of longitude at 70°N.

Stationary waves and slowly moving features in the night upper clouds of Venus

At the cloud top level of Venus (65-70 km altitude) the atmosphere rotates 60 times faster than the underlying surface, a phenomenon known as superrotation. Whereas on Venus's dayside the cloud top motions are well determined and Venus general circulation models predict a mean zonal flow at the upper clouds similar on both day and nightside, the nightside circulation remains poorly studied except for the polar region. Here we report global measurements of the nightside circulation at the upper cloud level. We tracked individual features in thermal emission images at 3.8 and 5.0 $\mathrm{\mu m}$ obtained between 2006 and 2008 by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS-M) onboard Venus Express and in 2015 by ground-based measurements with the Medium-Resolution 0.8-5.5 Micron Spectrograph and Imager (SpeX) at the National Aeronautics and Space Administration Infrared Telescope Facility (NASA/IRTF). The zonal motions range from -110 to -60 m s$^{-1}$, consistent with those found for the dayside but with larger dispersion. Slow motions (-50 to -20 m s$^{-1}$) were also found and remain unexplained. In addition, abundant stationary wave patterns with zonal speeds from -10 to +10 m s$^{-1}$ dominate the night upper clouds and concentrate over the regions of higher surface elevation.

Jupiter's polar ionospheric flows: High resolution mapping of spectral intensity and line‐of‐sight velocity of H3+ ions

AbstractWe present a detailed study of the auroral emission at Jupiter, which uses data taken on 31 December 2012 with the long‐slit echelle spectrometer Cryogenic Infrared Echelle Spectrograph (European Southern Observatory's Very Large Telescope). The entire northern auroral region was observed using significantly more slit positions than previous studies, providing a highly detailed view of ionospheric flows, which were mapped onto polar projections. Previous observations of ionospheric flows in Jupiter's northern auroral ionosphere, using the long‐slit echelle spectrometer CSHELL (NASA Infrared Telescope Facility) to measure the Doppler‐shifted ν 2 Q(1,0−) line at 3.953 μm, showed a strongly subrotating region that was nearly stationary in the inertial magnetic frame of reference, suggesting an interaction with the solar wind. In this work, we observe this stationary region coincident with a polar region with very weak infrared emission, typically described as the dark region in UV observations. Although our observations cannot determine the exact mechanisms of this coupling, the coincidence between solar wind controlled ionospheric flows and a region with very low auroral brightness may provide new insights into the nature of the solar wind coupling. We also detected a superrotating ionospheric flow measured both at and equatorward of the narrow bright portion of the main auroral emission. The origin of this flow remains uncertain. Additionally, we detect a strong velocity shear poleward of the peak in brightness of the main auroral emission. This is in agreement with past models which predict that conductivity, as well as velocity shear, plays an important role in generating the main auroral emission.

The Extended IRTF Spectral Library: Expanded Coverage in Metallicity, Temperature, and Surface Gravity

Abstract We present a 0.7–2.5 μm spectral library of 284 stars observed with the medium-resolution infrared spectrograph, SpeX, at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Maunakea, Hawaii. This library extends the metallicity range of the IRTF Cool Star library beyond solar metallicity to −1.7 < [Fe/H] < 0.6. All of the observed stars are also in the MILES optical stellar library, providing continuous spectral coverage for each star from 0.35 to 2.5 μm. The spectra are absolute flux calibrated using Two Micron All Sky Survey photometry, and the continuum shape of the spectra is preserved during the data reduction process. Synthesized JHK S colors agree with observed colors at the 1%–2% level, on average. We also present a spectral interpolator that uses the library to create a data-driven model of spectra as a function of , , and [Fe/H]. We use the library and interpolator to compare empirical trends with theoretical predictions of spectral feature behavior as a function of stellar parameters. These comparisons extend to the previously difficult to access low-metallicity and cool dwarf regimes, as well as the previously poorly sampled super-solar metallicity regime. The library and interpolator are publicly available.

Multiple‐wavelength sensing of Jupiter during the Juno mission's first perijove passage

AbstractWe compare Jupiter observations made around 27 August 2016 by Juno's JunoCam, Jovian Infrared Auroral Mapper (JIRAM), MicroWave Radiometer (MWR) instruments, and NASA's Infrared Telescope Facility. Visibly dark regions are highly correlated with bright areas at 5 µm, a wavelength sensitive to gaseous NH3 gas and particulate opacity at p ≤5 bars. A general correlation between 5‐µm and microwave radiances arises from a similar dependence on NH3 opacity. Significant exceptions are present and probably arise from additional particulate opacity at 5 µm. JIRAM spectroscopy and the MWR derive consistent 5‐bar NH3 abundances that are within the lower bounds of Galileo measurement uncertainties. Vigorous upward vertical transport near the equator is likely responsible for high NH3 abundances and with enhanced abundances of some disequilibrium species used as indirect indicators of vertical motions.

A deep search for the release of volcanic gases on Mars using ground-based high-resolution infrared and submillimeter spectroscopy: Sensitive upper limits for OCS and SO2

Recent volcanic activity has long been considered a distinct possibility that would place major constraints on the evolution of Mars’ interior. Volcanic activity would result in the outgassing of sulfur-bearing species. As part of our multi-band search for active release of volcanic gases on Mars, we looked for carbonyl sulfide (OCS) at its combination band (ν1+ν3) at 3.42 µ m (2924 cm−1), and sulfur dioxide (SO2) at 346.652 GHz, in two successive Mars years during its late Northern spring and mid Northern summer seasons (Ls= 43°–144°). The targeted volcanic districts, Tharsis and Syrtis Major, were observed during the two intervals, 15 Dec. 2011 to 6 Jan. 2012 in the first year, and 23 May 2014 to 12 June 2014 in the second year using the high resolution infrared spectrometer CSHELL on the NASA Infrared Telescope Facility, and the high resolution heterodyne receiver HARP at the James Clerk Maxwell Telescope atop Maunakea, Hawaii. No active release of such gases was detected, and we report 2σ upper limits of 1.8 ppbv and 3.1 ppbv for OCS and SO2, respectively, compared to 0.3 ppbv for SO2 (Encrenaz, T. et al. [2011] Astron. & Astrophys. 530, A37; Krasnopolsky, V.A. [2012] Icarus 217, 144–152) over the disk of Mars. Our retrieved upper limit on the SO2 outgassing rate of 156 tons/day (1.8 kg/s), corresponds to a mass rate of magma that is able to degas the SO2 of 104 kilotons/day (1200 kg/s), or 40,000 m3/day (0.46 m3/s). Our campaign places stringent limits on the concentration of sulfur-bearing species into the atmosphere of Mars.

The Great Cold Spot in Jupiter's upper atmosphere.

Past observations and modeling of Jupiter's thermosphere have, due to their limited resolution, suggested that heat generated by the aurora near the poles results in a smooth thermal gradient away from these aurorae, indicating a quiescent and diffuse flow of energy within the subauroral thermosphere. Here we discuss Very Large Telescope‐Cryogenic High‐Resolution IR Echelle Spectrometer observations that reveal a small‐scale localized cooling of ~200 K within the nonauroral thermosphere. Using Infrared Telescope Facility NSFCam images, this feature is revealed to be quasi‐stable over at least a 15 year period, fixed in magnetic latitude and longitude. The size and shape of this “Great Cold Spot” vary significantly with time, strongly suggesting that it is produced by an aurorally generated weather system: the first direct evidence of a long‐term thermospheric vortex in the solar system. We discuss the implications of this spot, comparing it with short‐term temperature and density variations at Earth.

Evidence for OH or H2O on the surface of 433 Eros and 1036 Ganymed

Water and hydroxyl, once thought to be found only in the primitive airless bodies that formed beyond roughly 2.5–3AU, have recently been detected on the Moon and Vesta, which both have surfaces dominated by evolved, non-primitive compositions. In both these cases, the water/OH is thought to be exogenic, either brought in via impacts with comets or hydrated asteroids or created via solar wind interactions with silicates in the regolith or both. Such exogenic processes should also be occurring on other airless body surfaces. To test this hypothesis, we used the NASA Infrared Telescope Facility (IRTF) to measure reflectance spectra (2.0–4.1µm) of two large near-Earth asteroids (NEAs) with compositions generally interpreted as anhydrous: 433 Eros and 1036 Ganymed. OH is detected on both of these bodies in the form of absorption features near 3µm. The spectra contain a component of thermal emission at longer wavelengths, from which we estimate thermal inertias of 167±98Jm−2s−1/2K−1 for Eros (consistent with previous estimates) and 214±80Jm−2s−1/2K−1 for Ganymed, the first reported measurement of thermal inertia for this object. These observations demonstrate that processes responsible for water/OH creation on large airless bodies also act on much smaller bodies.

Thermal properties and an improved shape model for near-Earth asteroid (162421) 2000 ET70

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 × 2.2 km × 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 h (± 0.009 h) and a north pole direction of ecliptic coordinates (52∘,−60∘)±6∘. 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 of this asteroid.

The Abundance of C2H4 in the Circumstellar Envelope of IRC+10216.

High spectral resolution mid-IR observations of ethylene (C2H4) towards the AGB star IRC+10216 were obtained using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). Eighty ro-vibrational lines from the 10.5 µm vibrational mode ν7 with J ≲ 30 were detected in absorption. The observed lines are divided into two groups with rotational temperatures of 105 and 400 K (warm and hot lines). The warm lines peak at ≃ -14 km s-1 with respect to the systemic velocity, suggesting that they are mostly formed outwards from ≃ 20R⋆. The hot lines are centered at -10 km s-1 indicating that they come from a shell between 10 and 20R⋆. 35% of the observed lines are unblended and can be fitted with a code developed to model the emission of a spherically symmetric circumstellar envelope. The analysis of several scenarios reveal that the C2H4 abundance relative to H2 in the range 5 - 20R⋆ is 6.9 × 10-8 in average and it could be as high as 1.1 × 10-7. Beyond 20R⋆, it is 8.2 × 10-8. The total column density is (6.5 ± 3.0) × 1015 cm-2. C2H4 is found to be rotationally under local thermodynamical equilibrium (LTE) and vibrationally out of LTE. One of the scenarios that best reproduce the observations suggests that up to 25% of the C2H4 molecules at 20R⋆ could condense onto dust grains. This possible depletion would not influence significantly the gas acceleration although it could play a role in the surface chemistry on the dust grains.

LOW-RESOLUTION NEAR-INFRARED STELLAR SPECTRA OBSERVED BY THE COSMIC INFRARED BACKGROUND EXPERIMENT (CIBER)

ABSTRACT We present near-infrared (0.8–1.8 μm) spectra of 105 bright ( < 10) stars observed with the low-resolution spectrometer on the rocket-borne Cosmic Infrared Background Experiment. As our observations are performed above the Earth's atmosphere, our spectra are free from telluric contamination, which makes them a unique resource for near-infrared spectral calibration. Two-Micron All-Sky Survey photometry information is used to identify cross-matched stars after reduction and extraction of the spectra. We identify the spectral types of the observed stars by comparing them with spectral templates from the Infrared Telescope Facility library. All the observed spectra are consistent with late F to M stellar spectral types, and we identify various infrared absorption lines.

DETECTION OF WATER AND/OR HYDROXYL ON ASTEROID (16) Psyche

ABSTRACT In order to search for evidence of hydration on M-type asteroid (16) Psyche, we observed this object in the 3 μm spectral region using the long-wavelength cross-dispersed (LXD: 1.9–4.2 μm) mode of the SpeX spectrograph/imager at the NASA Infrared Telescope Facility. Our observations show that Psyche exhibits a 3 μm absorption feature, attributed to water or hydroxyl. The 3 μm absorption feature is consistent with the hydration features found on the surfaces of water-rich asteroids, attributed to OH- and/or H2O-bearing phases (phyllosilicates). The detection of a 3 μm hydration absorption band on Psyche suggests that this asteroid may not be a metallic core, or it could be a metallic core that has been impacted by carbonaceous material over the past 4.5 Gyr. Our results also indicate rotational spectral variations, which we suggest reflect heterogeneity in the metal/silicate ratio on the surface of Psyche.

DETECTION OF ROTATIONAL SPECTRAL VARIATION ON THE M-TYPE ASTEROID (16) PSYCHE

ABSTRACT The asteroid (16) Psyche is of scientific interest because it contains ∼1% of the total mass of the asteroid belt and is thought to be the remnant metallic core of a protoplanet. Radar observations have indicated the significant presence of metal on the surface with a small percentage of silicates. Prior ground-based observations showed rotational variations in the near-infrared (NIR) spectra and radar albedo of this asteroid. However, no comprehensive study that combines multi-wavelength data has been conducted so far. Here we present rotationally resolved NIR spectra (0.7–2.5 μm) of (16) Psyche obtained with the NASA Infrared Telescope Facility. These data have been combined with shape models of the asteroid for each rotation phase. Spectral band parameters extracted from the NIR spectra show that the pyroxene band center varies from ∼0.92 to 0.94 μm. Band center values were used to calculate the pyroxene chemistry of the asteroid, whose average value was found to be Fs30En65Wo5. Variations in the band depth (BD) were also observed, with values ranging from 1.0% to 1.5%. Using a new laboratory spectral calibration method, we estimated an average orthopyroxene content of 6% ± 1%. The mass-deficit region of Psyche, which exhibits the highest radar albedo, also shows the highest value for the spectral slope and the minimum BD. The spectral characteristics of Psyche suggest that its parent body did not have the typical structure expected for a differentiated body or that the sequence of events that led to its current state was more complex than previously thought.

The size-frequency distribution of H > 13 NEOs and ARM target candidates detected by Pan-STARRS1

We determine the absolute magnitude (H) distribution (or size-frequency distribution, SFD; N(H)∝10αH where α is the slope of the distribution) for near-Earth objects (NEO) with 13 < H < 30 and Asteroid Retrieval Mission (ARM) targets with 27 < H < 31 that were detected by the 1st telescope of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1; e.g. Kaiser et al., 2002; Kaiser, 2004; Hodapp et al., 2004). The NEO and ARM target detection efficiencies were calculated using the Greenstreet et al. (2012) NEO orbit distribution. The debiased Pan-STARRS1 NEO absolute magnitude distribution is more complex than a single slope power law - it shows two transitions - at H ∼ 16 from steep to shallow slope, and in the 21 < H < 23 interval from a shallow to steep slope, which is consistent with other recent works (e.g. Mainzer et al., 2011c; Brown et al., 2013; Harris and D’Abramo, 2015). We fit α=0.48±0.02 for NEOs with 13 < H < 16, α=0.33±0.01 for NEOs with 16 < H < 22, and α=0.62±0.03 for the smaller objects with H > 22. There is also another change in slope from steep to shallow around H = 27. The three ARM target candidates detected by Pan-STARRS1 in one year of surveying have a corrected SFD with slope α=0.40−0.45+0.33.We also show that the window for follow up observations of small (H≳ 22) NEOs with the NASA IRTF telescope and Arecibo and Goldstone radars are extremely short - on order of days, and procedures for fast response must be implemented in order to measure physical characteristics of small Earth-approaching objects. CFHT’s MegaCam and Pan-STARRS1 have longer observing windows and are capable of following-up more NEOs due to their deeper limiting magnitudes and wider fields of view.

Hungaria asteroid region telescopic spectral survey (HARTSS) I: Stony asteroids abundant in the Hungaria background population

The Hungaria asteroids remain as survivors of late giant planet migration that destabilized a now extinct inner portion of the primordial asteroid belt and left in its wake the current resonance structure of the Main Belt. In this scenario, the Hungaria region represents a “purgatory” for the closest, preserved samples of the asteroidal material from which the terrestrial planets accreted. Deciphering the surface composition of these unique samples may provide constraints on the nature of the primordial building blocks of the terrestrial planets. We have undertaken an observational campaign entitled the Hungaria Asteroid Region Telescopic Spectral Survey (HARTSS) to record near-infrared (NIR) reflectance spectra in order to characterize their taxonomy, surface mineralogy, and potential meteorite analogs. The overall objective of HARTSS is to evaluate the compositional diversity of asteroids located throughout the Hungaria region. This region harbors a collisional family of Xe-type asteroids, which are situated among a background (i.e., non-family) of predominantly S-complex asteroids. In order to assess the compositional diversity of the Hungaria region, we have targeted background objects during Phase I of HARTSS. Collisional family members likely reflect the composition of one original homogeneous parent body, so we have largely avoided them in this phase. We have employed NIR instruments at two ground-based telescope facilities: the NASA Infrared Telescope Facility (IRTF), and the Telescopio Nazionale Galileo (TNG). Our data set includes the NIR spectra of 42 Hungaria asteroids (36 background; 6 family). We find that stony S-complex asteroids dominate the Hungaria background population (29/36 objects; ∼80%). C-complex asteroids are uncommon (2/42; ∼5%) within the Hungaria region. Background S-complex objects exhibit considerable spectral diversity as band parameter measurements of diagnostic absorption features near 1- and 2-µm indicate that several different S-subtypes are represented therein, which translates to a variety of surface compositions. We identify the Gaffey S-subtype (Gaffey et al. [1993]. Icarus 106, 573–602) and potential meteorite analogs for 24 of these S-complex background asteroids. Additionally, we estimate the olivine and orthopyroxene mineralogy for 18 of these objects using spectral band parameter analysis established from laboratory-based studies of ordinary chondrite meteorites. Nine of the asteroids have band parameters that are not consistent with ordinary chondrites. We compared these to the band parameters measured from laboratory VIS+NIR spectra of six primitive achondrite (acapulcoite-lodranite) meteorites. These comparisons suggest that two main meteorite groups are represented among the Hungaria background asteroids: unmelted, nebular l- (and possibly LL-ordinary chondrites), and partially-melted primitive achondrites of the acapulcoite-lodranite meteorite clan. Our results suggest a source region for L chondrite like material from within the Hungarias, with delivery to Earth via leakage from the inner boundary of the Hungaria region. H chondrite like mineralogies appear to be absent from the Hungaria background asteroids. We therefore conclude that the Hungaria region is not a source for H chondrite meteorites. Seven Hungaria background asteroids have spectral band parameters consistent with partially-melted primitive achondrites, but the probable source region of the acapulcoite-lodranite parent body remains inconclusive. If the proposed connection with the Hungaria family to fully-melted enstatite achondrite meteorites (i.e., aubrites) is accurate (Gaffey et al. [1992]. Icarus 100, 95–109; Kelley and Gaffey [2002]. Meteorit. Planet. Sci. 37, 1815–1827), then asteroids in the Hungaria region exhibit a full range of petrologic evolution: from nebular, unmelted ordinary chondrites, through partially-melted primitive achondrites, to fully-melted igneous aubrite meteorites.