arXiv subjects

Will M. Grundy

Publications and source records attributed to Will M. Grundy.

12 recordsLinked to original sources

arXiv2025

Orbital Characterization of a Newly Discovered Small Satellite Around Quaoar

Recent observations of a stellar occultation have revealed the presence of a previously undiscovered small satellite around Quaoar. Orbiting near Quaoar's unusual ring system, this new satellite has the potential to provide significant insights into the formation and evolution of Quaoar and its ring system. In this letter, we characterize the orbit of this newly discovered satellite, finding that it is likely on a $3.6^{+0.5}_{-0.3}$-day orbit, plausibly placing it near a 5:3 mean motion resonance with Quaoar's outermost known ring. Examining the possibility of observing the newly discovered satellite with further stellar occultations, we estimate that $\sim$hundreds of observing stations are required for recovery, since phase information about its orbit was rapidly lost after the lone detection. We also attempted to recover the satellite in JWST NIRCam imaging of Quaoar, but find no convincing detection. This non-detection is limited by the accuracy of the available NIRCam PSF models, as well as the satellite's extreme faintness and close-in orbital separation. Therefore, current-generation telescopes will likely struggle to directly image this new satellite, but near-future 30-meter-class telescopes should prove capable of detecting it. Discovery of such a satellite provides evidence that the rings around Quaoar may have been part of an initially broad collisional disk that has evolved considerably since its formation. To further explore this hypothesis, we encourage follow-up observations of the rings and satellites with stellar occultations and direct imaging, as well as updated hydrodynamical, collisional, and tidal modeling of the system.

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arXiv2025

JWST sighting of decameter main-belt asteroids and view on meteorite sources

Asteroid discoveries are essential for planetary-defense efforts aiming to prevent impacts with Earth, including the more frequent megaton explosions from decameter impactors. While large asteroids ($\geq$100 km) have remained in the main belt since their formation, small asteroids are commonly transported to the near-Earth object (NEO) population. However, due to the lack of direct observational constraints, their size-frequency distribution--which informs our understanding of the NEOs and the delivery of meteorite samples to Earth--varies significantly among models. Here, we report 138 detections of the smallest asteroids ($\gtrapprox $10 m) ever observed in the main belt, which were enabled by JWST's infrared capabilities covering the asteroids' emission peaks and synthetic tracking techniques. Despite small orbital arcs, we constrain the objects' distances and phase angles using known asteroids as proxies, allowing us to derive sizes via radiometric techniques. Their size-frequency distribution exhibits a break at ${\sim}100$ m (debiased cumulative slopes of $q = -2.66\pm0.60$ and $-0.97\pm0.14$ for diameters smaller and larger than $\sim $100 m, respectively), suggestive of a population driven by collisional cascade. These asteroids were sampled from multiple asteroid families--most likely Nysa, Polana and Massalia--according to the geometry of pointings considered here. Through additional long-stare infrared observations, JWST is poised to serendipitously detect thousands of decameter-scale asteroids across the sky, probing individual asteroid families and the source regions of meteorites "in-situ".

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arXiv2024

Beyond Point Masses. III. Detecting Haumea's Nonspherical Gravitational Field

The dwarf planet Haumea is one of the most compelling transneptunian objects (TNOs) to study, hosting two small, dynamically interacting satellites, a family of nearby spectrally unique objects, and a ring system. Haumea itself is extremely oblate due to its 3.9 hour rotation period. Understanding the orbits of Haumea's satellites, named Hi'iaka and Namaka, requires detailed modeling of both satellite-satellite gravitational interactions and satellite interactions with Haumea's nonspherical gravitational field (parameterized here as $J_2$). Understanding both of these effects allows for a detailed probe of the satellites' masses and Haumea's $J_2$ and spin pole. Measuring Haumea's $J_2$ provides information about Haumea's interior, possibly determining the extent of past differentation. In an effort to understand the Haumea system, we have performed detailed non-Keplerian orbit fitting of Haumea's satellites using a decade of new ultra-precise observations. Our fits detect Haumea's $J_2$ and spin pole at $\gtrsim2.5σ$ confidence. Degeneracies present in the dynamics prevent us from precisely measuring Haumea's $J_2$ with the current data, but future observations should enable a precise measurement. Our dynamically determined spin pole shows excellent agreement with past results, illustrating the strength of non-Keplerian orbit fitting. We also explore the spin-orbit dynamics of Haumea and its satellites, showing that axial precession of Hi'iaka may be detectable over decadal timescales. Finally, we present an ephemeris of the Haumea system over the coming decade, enabling high-quality observations of Haumea and its satellites for years to come.

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arXiv2024

The Equilibrium Vapor Pressures of Ammonia and Oxygen Ices at Outer Solar System Temperatures

Few laboratory studies have investigated the vapor pressures of the volatiles that may be present as ices in the outer solar system; even fewer studies have investigated these species at the temperatures and pressures suitable to the surfaces of icy bodies in the Saturnian and Uranian systems ($\lt$100 K, $\lt10^{-9}$ bar). This study adds to the work of Grundy et al. (2024) in extending the known equilibrium vapor pressures of outer solar system ices through laboratory investigations at very low temperatures. Our experiments with ammonia and oxygen ices provide new thermodynamic models for these species' respective enthalpies of sublimation. We find that ammonia ice, and to a lesser degree oxygen ice, are stable at higher temperatures than extrapolations in previous literature have predicted. Our results show that these ices should be retained over longer periods of time than previous extrapolations would predict, and a greater amount of these solids is required to support observation in exospheres of airless bodies in the outer solar system.

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arXiv2022

Ultraviolet Spectroscopy of Lucy Mission Targets with the Hubble Space Telescope

The recently launched Lucy mission aims to understand the dynamical history of the Solar System by examining the Jupiter Trojans, a population of primitive asteroids co-orbital with Jupiter. Using the G280 grism on the Hubble Space Telescope's Wide Field Camera 3 we obtained near ultraviolet spectra of four of the five Lucy mission targets -- (617) Patroclus-Menoetius, (11351) Leucus, (3548) Eurybates, and (21900) Orus -- to search for novel spectral features. We observe a local reflectance minimum at 0.4 $μ$m accompanied by an increase in reflectance from 0.35-0.3 $μ$m in the spectra of Patroclus and Orus. We use the principles of Rayleigh scattering and geometric optics to develop a Hapke optical model to investigate whether this feature can be explained by the presence of submicroscopic grains on Trojan surfaces. The near ultraviolet "bump" feature can be explained by scattering due to fine-grained opaques (iron, amorphous carbon, or graphite) with grain sizes ranging from 20 - 80 nm.

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arXiv2021

Hypotheses for Triton's Plumes: New Analyses and Future Remote Sensing Tests

At least two active plumes were observed on Neptune's moon Triton during the Voyager 2 flyby in 1989. Models for Triton's plumes have previously been grouped into five hypotheses, two of which are primarily atmospheric phenomena and are generally considered unlikely, and three of which include eruptive processes and are plausible. These hypotheses are compared, including new arguments, such as comparisons based on current understanding of Mars, Enceladus, and Pluto. An eruption model based on a solar-powered, solid-state greenhouse effect was previously considered the leading hypothesis for Triton's plumes, in part due to the proximity of the plumes to the subsolar latitude during the Voyager 2 flyby and the distribution of Triton's fans that are putatively deposits from former plumes. The other two eruption hypotheses are powered by internal heat, not solar insolation. Based on new analyses of the ostensible relation between the latitude of the subsolar point on Triton and the geographic locations of the plumes and fans, we argue that neither the locations of the plumes nor fans are strong evidence in favor of the solar-powered hypothesis. We conclude that all three eruption hypotheses should be considered further. Five tests are presented that could be implemented with remote sensing observations from future spacecraft to confidently distinguish among the eruption hypotheses for Triton's plumes. The five tests are based on the: (1) composition and thickness of Triton's southern hemisphere terrains, (2) composition of fan deposits, (3) distribution of active plumes, (4) distribution of fans, and (5) surface temperature at the locations of plumes and/or fans. The tests are independent, but complementary, and implementable with a single flyby mission such as the Trident mission concept. We note that, in the case of the solar-driven hypothesis, the 2030s and 2040s may be the last ...

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arXiv2016

OSSOS: IV. Discovery of a dwarf planet candidate in the 9:2 resonance with Neptune

We report the discovery and orbit of a new dwarf planet candidate, 2015 RR$_{245}$, by the Outer Solar System Origins Survey (OSSOS). 2015 RR$_{245}$'s orbit is eccentric ($e=0.586$), with a semi-major axis near 82 au, yielding a perihelion distance of 34 au. 2015 RR$_{245}$ has $g-r = 0.59 \pm 0.11$ and absolute magnitude $H_{r} = 3.6 \pm 0.1$; for an assumed albedo of $p_V = 12$% the object has a diameter of $\sim670$ km. Based on astrometric measurements from OSSOS and Pan-STARRS1, we find that 2015 RR$_{245}$ is securely trapped on ten-Myr timescales in the 9:2 mean-motion resonance with Neptune. It is the first TNO identified in this resonance. On hundred-Myr timescales, particles in 2015 RR$_{245}$-like orbits depart and sometimes return to the resonance, indicating that 2015 RR$_{245}$ likely forms part of the long-lived metastable population of distant TNOs that drift between resonance sticking and actively scattering via gravitational encounters with Neptune. The discovery of a 9:2 TNO stresses the role of resonances in the long-term evolution of objects in the scattering disk, and reinforces the view that distant resonances are heavily populated in the current Solar System. This object further motivates detailed modelling of the transient sticking population.

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arXiv2016

The Outer Solar System Origins Survey: I. Design and First-Quarter Discoveries

We report the discovery, tracking and detection circumstances for 85 trans-Neptunian objects (TNOs) from the first 42 deg$^{2}$ of the Outer Solar System Origins Survey (OSSOS). This ongoing $r$-band Solar System survey uses the 0.9 deg$^{2}$ field-of-view MegaPrime camera on the 3.6 m Canada-France-Hawaii Telescope. Our orbital elements for these TNOs are precise to a fractional semi-major axis uncertainty $<0.1\%$. We achieve this precision in just two oppositions, as compared to the normal 3-5 oppositions, via a dense observing cadence and innovative astrometric technique. These discoveries are free of ephemeris bias, a first for large trans-Neptunian surveys. We also provide the necessary information to enable models of TNO orbital distributions to be tested against our TNO sample. We confirm the existence of a cold "kernel" of objects within the main cold classical Kuiper belt, and infer the existence of an extension of the "stirred" cold classical Kuiper belt to at least several AU beyond the 2:1 mean motion resonance with Neptune. We find that the population model of Petit et al. (2011) remains a plausible representation of the Kuiper belt. The full survey, to be completed in 2017, will provide an exquisitely characterized sample of important resonant TNO populations, ideal for testing models of giant planet migration during the early history of the Solar System.

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arXiv2016

Discovery of a Makemakean Moon

We describe the discovery of a satellite in orbit about the dwarf planet (136472) Makemake. This satellite, provisionally designated S/2015 (136472) 1, was detected in imaging data collected with the Hubble Space Telescope's Wide Field Camera 3 on UTC April 27, 2015 at 7.80$\pm$0.04 magnitudes fainter than Makemake. It likely evaded detection in previous satellite searches due to a nearly edge-on orbital configuration, placing it deep within the glare of Makemake during a substantial fraction of its orbital period. This configuration would place Makemake and its satellite near a mutual event season. Insufficient orbital motion was detected to make a detailed characterization of its orbital properties, prohibiting a measurement of the system mass with the discovery data alone. Preliminary analysis indicates that if the orbit is circular, its orbital period must be longer than 12.4 days, and must have a semi-major axis $\gtrsim$21,000 km. We find that the properties of Makemake's moon suggest that the majority of the dark material detected in the system by thermal observations may not reside on the surface of Makemake, but may instead be attributable to S/2015 (136472) 1 having a uniform dark surface. This "dark moon hypothesis" can be directly tested with future JWST observations. We discuss the implications of this discovery for the spin state, figure, and thermal properties of Makemake and the apparent ubiquity of trans-Neptunian dwarf planet satellites.

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arXiv2016

The Geology of Pluto and Charon Through the Eyes of New Horizons

NASA's New Horizons spacecraft has revealed the complex geology of Pluto and Charon. Pluto's encounter hemisphere shows ongoing surface geological activity centered on a vast basin containing a thick layer of volatile ices that appears to be involved in convection and advection, with a crater retention age no greater than $\approx$10 Ma. Surrounding terrains show active glacial flow, apparent transport and rotation of large buoyant water-ice crustal blocks, and pitting, likely by sublimation erosion and/or collapse. More enigmatic features include tall mounds with central depressions that are conceivably cryovolcanic, and ridges with complex bladed textures. Pluto also has ancient cratered terrains up to ~4 Ga old that are extensionally fractured and extensively mantled and perhaps eroded by glacial or other processes. Charon does not appear to be currently active, but experienced major extensional tectonism and resurfacing (probably cryovolcanic) nearly 4 billion years ago. Impact crater populations on Pluto and Charon are not consistent with the steepest proposed impactor size-frequency distributions proposed for the Kuiper belt.

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arXiv2004

The Orbit and Albedo of Transneptunian Binary 1997 CQ29

We have measured the separations and position angles of the two components of the binary transneptunian object 1997 CQ29 at eight epochs. From these data we are able to constrain the orbit and mass of this binary system. The best fitting orbit has an orbital period of P = 312+/-3 days. The orbital eccentricity is e = 0.45+/-0.03 and the semimajor axis is a = 8,010+/-80 km. The mass of the system is surprisingly low at 0.42+/-0.02 x 10^18 kg. To account for the observed brightness consistent with the low mass and a range of plausible densities, the geometric albedo must be very high; for an assumed density of 1000 kg m^-3 we find a red geometric albedo of p_R = 0.37, an order of magnitude higher than has been generally assumed for transneptunian objects. If objects with comparably high albedos are common in the Kuiper belt, estimates of the mass of the belt must be significantly reduced. The semimajor axis of 1997 CQ29's orbit is 2.8% of the Hill radius of the primary, a value strikingly similar to this same ratio in other transneptunian binaries, main-belt binaries, and regular satellite systems.

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arXiv2002

Detection of Two Binary Trans-Neptunian Objects, 1997 CQ29 and 2000 CF105, with the Hubble Space Telescope

Images of the trans-Neptunian objects 1997 CQ29 and 2000 CF105 obtained with the Hubble Space Telescope's WFPC2 camera show them to be binary. The two components of 1997 CQ29 were separated in our images by 0.20 arcsec in November 2001 and by 0.33 arcsec in June/July 2002. The corresponding minimum physical distances are 6100 km and 10,200 km. The companion to 2000 CF105 was 0.78 arcsec from the primary, at least 23,400 km. Six other objects in the trans-Neptunian region, including Pluto and its moon Charon, are known to be binaries; 1997 CQ29 and 2000 CF105 are the seventh and eighth known pair. Binarity appears to be a not-uncommon characteristic in this region of the solar system, with detectable companions present in 4% of the objects we have examined.

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