arXiv subjects

David E. Trilling

Publications and source records attributed to David E. Trilling.

71 records · Page 4Linked to original sources

arXiv2015

Distribution of CO2 ice on the large moons of Uranus and evidence for compositional stratification of their near-surfaces

The surfaces of the large Uranian satellites are characterized by a mixture of H2O ice and a dark, potentially carbon-rich, constituent, along with CO2 ice. At the mean heliocentric distance of the Uranian system, native CO2 ice should be removed on timescales shorter than the age of the Solar System. Consequently, the detected CO2 ice might be actively produced. Analogous to irradiation of icy moons in the Jupiter and Saturn systems, we hypothesize that charged particles caught in Uranus' magnetic field bombard the surfaces of the Uranian satellites, driving a radiolytic CO2 production cycle. To test this hypothesis, we investigated the distribution of CO2 ice by analyzing near-infrared (NIR) spectra of these moons, gathered using the SpeX spectrograph at NASA's Infrared Telescope Facility (IRTF) (2000 - 2013). Additionally, we made spectrophotometric measurements using images gathered by the Infrared Array Camera (IRAC) onboard the Spitzer Space Telescope (2003 - 2005). We find that the detected CO2 ice is primarily on the trailing hemispheres of the satellites closest to Uranus, consistent with other observations of these moons. Our band parameter analysis indicates that the detected CO2 ice is pure and segregated from other constituents. Our spectrophotometric analysis indicates that IRAC is not sensitive to the CO2 ice detected by SpeX, potentially because CO2 is retained beneath a thin surface layer dominated by H2O ice that is opaque to photons over IRAC wavelengths. Thus, our combined SpeX and IRAC analyses suggest that the near-surfaces (i.e., top few 100 microns) of the Uranian satellites are compositionally stratified. We briefly compare the spectral characteristics of the CO2 ice detected on the Uranian moons to icy satellites elsewhere, and we also consider the most likely drivers of the observed distribution of CO2 ice.

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arXiv2013

The Discovery of Cometary Activity in Near-Earth Asteroid (3552) Don Quixote

The near-Earth object (NEO) population, which mainly consists of fragments from collisions between asteroids in the main asteroid belt, is thought to include contributions from short-period comets as well. One of the most promising NEO candidates for a cometary origin is near-Earth asteroid (3552) Don Quixote, which has never been reported to show activity. Here we present the discovery of cometary activity in Don Quixote based on thermal-infrared observations made with the Spitzer Space Telescope in its 3.6 and 4.5 μm bands. Our observations clearly show the presence of a coma and a tail in the 4.5 μm but not in the 3.6 μm band, which is consistent with molecular band emission from CO2. Thermal modeling of the combined photometric data on Don Quixote reveals a diameter of 18.4 (-0.4/+0.3) km and an albedo of 0.03 (-0.01/+0.02), which confirms Don Quixote to be the third-largest known NEO. We derive an upper limit on the dust production rate of 1.9 kg s^-1 and derive a CO2 gas production rate of (1.1+-0.1)10^26 molecules s^-1. Spitzer IRS spectroscopic observations indicate the presence of fine-grained silicates, perhaps pyroxene rich, on the surface of Don Quixote. Our discovery suggests that CO2 can be present in near-Earth space over a long time. The presence of CO2 might also explain that Don Quixote's cometary nature remained hidden for nearly three decades.

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arXiv2013

Physical Characterization of Warm Spitzer-observed Near-Earth Objects

Near-infrared spectroscopy of Near-Earth Objects (NEOs) connects diagnostic spectral features to specific surface mineralogies. The combination of spectroscopy with albedos and diameters derived from thermal infrared observations can increase the scientific return beyond that of the individual datasets. To that end, we have completed a spectroscopic observing campaign to complement the ExploreNEOs Warm Spitzer program that obtained albedos and diameters of nearly 600 NEOs (Trilling et al. 2010). Here we present the results of observations using the low-resolution prism mode (~0.7-2.5 microns) of the SpeX instrument on the NASA Infrared Telescope Facility (IRTF). We also include near-infrared observations of ExploreNEOs targets from the MIT-UH-IRTF Joint Campaign for Spectral Reconnaissance. Our dataset includes near-infrared spectra of 187 ExploreNEOs targets (125 observations of 92 objects from our survey and 213 observations of 154 objects from the MIT survey). We identify a taxonomic class for each spectrum and use band parameter analysis to investigate the mineralogies for the S-, Q-, and V-complex objects. Our analysis suggests that for spectra that contain near-infrared data but lack the visible wavelength region, the Bus-DeMeo system misidentifies some S-types as Q-types. We find no correlation between spectral band parameters and ExploreNEOs albedos and diameters. We find slightly negative Band Area Ratio (BAR) correlations with phase angle for Eros and Ivar, but a positive BAR correlation with phase angle for Ganymed. We find evidence for spectral phase reddening for Eros, Ganymed, and Ivar. We identify the likely ordinary chondrite type analog for a subset of our sample. Our resulting proportions of H, L, and LL ordinary chondrites differ from those calculated for meteorite falls and in previous studies of ordinary chondrite-like NEOs.

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arXiv2013

Initial Planetesimal Sizes and the Size Distribution of Small Kuiper Belt Objects

We show, by comparing observations with theoretical models, that the observed Kuiper Belt size distribution is well matched by coagulation models, which start from an initial planetesimal population with radii of about 1km, and subsequent collisional evolution. We find that the observed size distribution for R > 30km has not been modified by collisional evolution over the age of the solar system, and that the size distribution below R ~ 30km has been modified by collisions and that its slope is well matched by collisional evolution models that use published strength laws. We investigate in detail the resulting size distribution of bodies ranging from 0.01km to 30km and find that its slope changes several times as a function of radius before approaching the expected value for an equilibrium collisional cascade of material strength dominated bodies for R < 0.1km. Compared to a single power law size distribution that would span the whole range from 0.01km to 30km, we find a strong deficit of bodies around R ~10km and a strong excess of bodies around 2km. This deficit and excess are caused by an excess mass in small planetesimals in the km size range that was left over from the runaway growth phase and that leaves a signature in the size distribution that is not erased after 4.5 Gyrs of collisional evolution. Observations of the small KBO size distribution can therefore test if large KBOs grew as a result of runaway growth and constrain the initial planetesimal sizes. We find that results from recent KBO occultation surveys and the observed KBO size distribution can be best matched by an initial planetesimal population that contained about equal mass per logarithmic mass bin in bodies ranging from 0.4km to 4km in radius. In addition, we find that we cannot match the observed KBO size distribution if most of the planetesimal mass was contained in bodies that were 10km in radius or larger.

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arXiv2013

2011 HM102: Discovery of a High-Inclination L5 Neptune Trojan in the Search for a post-Pluto New Horizons Target

We present the discovery of a long-term stable L5 (trailing) Neptune Trojan in data acquired to search for candidate Trans-Neptunian objects for the New Horizons spacecraft to fly by during an extended post-Pluto mission. This Neptune Trojan, 2011 HM102, has the highest inclination (29.4 degrees) of any known member of this population. It is intrinsically brighter than any single L5 Jupiter Trojan at H~8.18. We have determined its gri colors (a first for any L5 Neptune Trojan), which we find to be similar to the moderately red colors of the L4 Neptune Trojans, suggesting similar surface properties for members of both Trojan clouds. We also present colors derived from archival data for two L4 Neptune Trojans (2006 RJ103 and 2007 VL305), better refining the overall color distribution of the population. In this document we describe the discovery circumstances, our physical characterization of 2011 HM102, and this object's implications for the Neptune Trojan population overall. Finally, we discuss the prospects for detecting 2011 HM102 from the New Horizons spacecraft during their close approach in mid- to late-2013.

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arXiv2012

The Incidence of Debris Disks at 24 μm and 670 Myr

We use Spitzer Space Telescope 24 μm data to search for debris disks among 122 AFGKM stars from the \sim 670 Myr clusters Hyades, Coma Ber, and Praesepe, utilizing a number of advances in data reduction and determining the intrinsic colors of main sequence stars. For our sample, the 1σ dispersion about the main sequence V-K, K-[24] locus is approximately 3.1%. We identify seven debris disks at 10% or more (\geq 3σ confidence level) above the expected K-[24] for purely photospheric emission. The incidence of excesses of 10% or greater in our sample at this age is 5.7 +3.1/-1.7%. Combining with results from the literature, the rate is 7.8 +4.2/-2.1% for early- type (B9 - F4) stars and 2.7 +3.3/-1.7% for solar-like (F5 - K9) stars. Our primary sample has strict criteria for inclusion to allow comparison with other work; when we relax these criteria, three additional debris disks are detected. They are all around stars of solar-like type and hence reinforce our conclusion that disks around such stars are still relatively common at 670 Myr and are similar to the rate around early-type stars. The apparently small difference in decay rates between early-type and solar-like stars is inconsistent with the first order theoretical predictions that the later type stellar disks would decay an order of magnitude more quickly than the earlier type ones.

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arXiv2011

Dynamically Excited Outer Solar System Objects in the Hubble Space Telescope Archive

We present the faintest mid ecliptic latitude survey in the second part of HST archival search for outer Solar System bodies. We report the discovery of 28 new trans-Neptunian objects and 1 small centaur (R ~ 2km) in the band 5{\circ} - 20{\circ} off the ecliptic. The inclination distribution of these excited ob jects is consistent with the distribution derived from brighter ecliptic surveys. We suggest that the size and inclination distribution should be estimated consistently using suitable surveys with calibrated search algorithms and reliable orbital information.

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arXiv2010

The Structure of the β Leonis Debris Disk

We combine nulling interferometry at 10 μm using the MMT and Keck Telescopes with spectroscopy, imaging, and photometry from 3 to 100 μm using Spitzer to study the debris disk around β Leo over a broad range of spatial scales, corresponding to radii of 0.1 to ~100 AU. We have also measured the close binary star o Leo with both Keck and MMT interferometers to verify our procedures with these instruments. The β Leo debris system has a complex structure: 1.) relatively little material within 1 AU; 2.) an inner component with a color temperature of ~600 K, fitted by a dusty ring from about 2 to 3 AU; and 3.) a second component with a color temperature of ~120 K fitted by a broad dusty emission zone extending from about ~5 AU to ~55 AU. Unlike many other A-type stars with debris disks, β Leo lacks a dominant outer belt near 100 AU.

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arXiv2010

The inclinations of faint TNOs

Bernstein et al. (2004) found that the population of faint (R>26) trans-Neptunian objects (TNOs) known at that time was dominated by "Classical" objects, which have low inclinations (i<5 degrees) and distances 40--45 AU. Since those observations, the number of faint TNOs whose orbits are sufficiently well known to be classified as "Classical" or "Excited" has grown from seven to 39. We analyze the dynamical classifications of faint TNOs known today and find that this population is dominated by Excited objects. We discuss some implications of this result.

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arXiv2010

Trans-Neptunian Objects with Hubble Space Telescope ACS/WFC

We introduce a novel search technique that can identify trans-neptunian objects in three to five exposures of a pointing within a single Hubble Space Telescope orbit. The process is fast enough to allow the discovery of candidates soon after the data are available. This allows sufficient time to schedule follow up observations with HST within a month. We report the discovery of 14 slow-moving objects found within 5\circ of the ecliptic in archival data taken with the Wide Field Channel of the Advanced Camera for Surveys. The luminosity function of these objects is consistent with previous ground-based and space-based results. We show evidence that the size distribution of both high and low inclination populations is similar for objects smaller than 100 km, as expected from collisional evolution models, while their size distribution differ for brighter objects. We suggest the two populations formed in different parts of the protoplanetary disk and after being dynamically mixed have collisionally evolved together. Among the objects discovered there is an equal mass binary with an angular separation ~ 0."53.

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arXiv2007

Composition of the L5 Mars Trojans: Neighbors, not Siblings

Mars is the only terrestrial planet known to have Tro jan (co-orbiting) asteroids, with a confirmed population of at least 4 objects. The origin of these objects is not known; while several have orbits that are stable on solar-system timescales, work by Rivkin et al. (2003) showed they have compositions that suggest separate origins from one another. We have obtained infrared (0.8-2.5 micron) spectroscopy of the two largest L5 Mars Tro jans, and confirm and extend the results of Rivkin et al. (2003). We suggest that the differentiated angrite meteorites are good spectral analogs for 5261 Eureka, the largest Mars Trojan. Meteorite analogs for 101429 1998 VF31 are more varied and include primitive achondrites and mesosiderites.

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arXiv2007

Extra-Solar Kuiper Belt Dust Disks

The dust disks observed around mature stars are evidence that plantesimals are present in these systems on spatial scales that are similar to that of the asteroids and the KBOs in the Solar System. These dust disks (a.k.a. ``debris disks'') present a wide range of sizes, morphologies and properties. It is inferred that their dust mass declines with time as the dust-producing planetesimals get depleted, and that this decline can be punctuated by large spikes that are produced as a result of individual collisional events. The lack of solid state features indicate that, generally, the dust in these disks have sizes larger than approximately 10 microns, but exceptionally, strong silicate features in some disks suggest the presence of large quantities of small grains, thought to be the result of recent collisions. Spatially resolved observations of debris disks show a diversity of structural features, such as inner cavities, warps, offsets, brightness asymmetries, spirals, rings and clumps. There is growing evidence that, in some cases, these structures are the result of the dynamical perturbations of a massive planet. Our Solar System also harbors a debris disk and some of its properties resemble those of extra-solar debris disks. From the cratering record, we can infer that its dust mass has decayed with time, and that there was at least one major ``spike'' in the past during the Late Heavy Bombardment. This offers a unique opportunity to use extra-solar debris disks to shed some light in how the Solar System might have looked in the past. Similarly, our knowledge of the Solar System is influencing our understanding of the types of processes which might be at play in the extra-solar debris disks.

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arXiv2006

Spitzer 24 Micron Observations of Open Cluster IC 2391 and Debris Disk Evolution of FGK Stars

We present 24 micron Spitzer/MIPS photometric observations of the ~50 Myr open cluster IC 2391. Thirty-four cluster members ranging in spectral type from B3-M5 were observed in the central square degree of the cluster. Excesses indicative of debris disks were discovered around 1 A star, 6 FGK stars, and possibly 1 M dwarf. For the cluster members observed to their photospheric limit, we find a debris disk frequency of 10 (-3,+17)% for B-A stars and 31 (-9,+13)% for FGK stars using a 15% relative excess threshold. Relative to a model of decaying excess frequency, the frequency of debris disks around A-type stars appears marginally low for the cluster's age while that of FGK stars appears consistent. Scenarios that may qualitatively explain this result are examined. We conclude that planetesimal activity in the terrestrial region of FGK stars is common in the first ~50 Myr and decays on timescales of ~100 Myr. Despite luminosity differences, debris disk evolution does not appear to depend strongly on stellar mass.

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arXiv2005

Lightcurves of 20--100 kilometer Kuiper Belt Objects using the Hubble Space Telescope

We report high precision photometry of three small and one larger Kuiper Belt Objects (KBOs) obtained with the Advanced Camera for Surveys onboard the Hubble Space Telescope (ACS/HST). The three small bodies are the smallest KBOs for which lightcurve measurements are available. 2003 BF91 has a diameter of 20 kilometers (assuming 10% albedo) and a 1.09 magnitude, 9.1-hour lightcurve that is feasibly explained by the rotation of an elongated, coherent body that is supported by material strength and best imagined as an icy outer Solar System analog to asteroid (243) Ida. Two other small KBOs, 2003 BG91 and 2003 BH91 (diameters 31 and 18 km, with albedo 10%), exhibit an unremarkable lightcurve and no detectable photometric variation, respectively. For the larger KBO 2000 FV53 (116 km diameter, assuming 10% albedo) we strongly detect a non-sinusoidal periodic (7.5 hours) brightness variation with a very small amplitude (0.07 mag). This KBO may be nearly spherical, a result that might not be unusual in the Kuiper Belt but would be remarkable among outer Solar System satellites of similar size. We carry out a study of possible physical states and bulk densities under the assumptions of both fluid equilibrium and finite, non-zero internal friction. The densities for the these KBOs are likely to be in the range 1--2 g/cm3, and a plausible solution for 2000 FV53 is a rubble pile of this density that is held slightly out of the minimum-energy shape by internal friction among constituent blocks that are relatively small. Our interpretation of 2000 FV53 as a pulverized but essentially primordial object and 2003 BF91 as a collisional fragment is consistent with models of collisional timescales in the outer Solar System. We compile all published KBO lightcurve data and compare our results to the larger population. [abridged]

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arXiv2004

The impact of a close stellar encounter on the Edgeworth-Kuiper Belt

We numerically investigate the possibility that a close stellar encounter could account for the high inclinations of the Kuiper belt, as originally proposed by Ida, Larwood and Burkert, however we consider encounters with pericenters within those explored by previous works. A star of mass 0.2 Msol entering the solar system on a nearly parabolic, low inclination, retrograde orbit with perihelion of 50 AU can scatter ~30% of the Kuiper belt into moderate inclination (i>10 degrees) and eccentricity orbits, while leaving the rest of the belt at low eccentricities and inclinations. This scenario provides a possible explanation for the dichotomy of the Kuiper belt, accounting for the scattered and classical populations, including objects with high eccentricities and inclinations. High eccentricity objects that were not placed into resonance with Neptune are more likely to be removed from the system by subsequent long timescale evolution. Consequently this scenario suggests that some Plutinos could have originally been objects in circular orbits which were scattered into resonant high eccentricity and high inclination orbits by the stellar encounter. Objects could have been placed into stable resonant regions with Neptune by the encounter. However long lived regions of dynamical stability should differ from those selected by resonance capture. This scenario predicts the presence of objects in resonances with Neptune that are unlikely to have been captured via Neptune's migration.

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arXiv2002

Orbital migration and the frequency of giant planet formation

We present a statistical study of the post-formation migration of giant planets in a range of initial disk conditions. For given initial conditions we model the evolution of giant planet orbits under the influence of disk, stellar, and mass loss torques. We determine the mass and semi-major axis distribution of surviving planets after disk dissipation, for various disk masses, lifetimes, viscosities, and initial planet masses. The majority of planets migrate too fast and are destroyed via mass transfer onto the central star. Most surviving planets have relatively large orbital semi-major axes of several AU or larger. We conclude that the extrasolar planets observed to date, particularly those with small semi-major axes, represent only a small fraction (~25% to 33%) of a larger cohort of giant planets around solar-type stars, and many undetected giant planets must exist at large (>1-2 AU) distances from their parent stars. As sensitivity and completion of the observed sample increases with time, this distant majority population of giant planets should be revealed. We find that the current distribution of extrasolar giant planet masses implies that high mass (more than 1-2 Jupiter masses) giant planet formation must be relatively rare. Finally, our simulations imply that the efficiency of giant planet formation must be high: at least 10% and perhaps as many as 80% of solar-type stars possess giant planets during their pre-main sequence phase. These predictions, including those for pre-main sequence stars, are testable with the next generation of ground- and space-based planet detection techniques

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arXiv2001

Near-infrared coronagraphic imaging of the circumstellar disk around TW Hydrae

We present ground-based near-infrared (H-band) imaging of the circumstellar disk around the nearby classical T Tauri star TW Hydrae. The scattered light image shows a face-on disk with radius 4 arcseconds (corresponding to 225 AU) and a morphology which agrees with recent images from the Hubble Space Telescope and the Very Large Array. The best fit power-law for the disk's radial surface brightness profile obeys the law r^{-3.3\pm0.3}. We use our image and published continuum flux densities to derive properties of the disk with a simple model of emission from an optically thick, flat disk. The best-fit values for disk mass and inner radius are 0.03 M_{\odot} and 0.3 AU; best-fit values for temperature, density, and grain opacity power law exponents (q, p, and β) are 0.7, 1.3, and 0.9, respectively. These properties are similar to those of disks around classical T Tauri stars located in more distant molecular clouds. Because of TW Hydrae's nearby location and pole-on orientation, it is a uniquely favorable object for future studies of radial disk structure at the classical T Tauri stage.

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