arXiv subjects

Benjamin Proudfoot

Publications and source records attributed to Benjamin Proudfoot.

11 recordsLinked to original sources

arXiv2026

Beyond Point Masses. VI. Spin-Orbit Evolution of the Centaur Binary Typhon-Echidna

Only three binaries have been identified among the Centaur population. Because their perihelia are significantly closer than those of other trans-Neptunian binaries (TNBs), these systems allow a detailed look at tight binaries in the broader TNO population and provide critical insight into the disruption of binaries as they enter the Centaur population. Using recent and archival \textit{Hubble Space Telescope} (HST) observations, along with Keck data, we present a spin-orbit study of Typhon-Echidna. We find that the binary's mutual orbit is inconsistent with a Keplerian orbit; more detailed non-Keplerian fits show that the mutual orbit is rapidly precessing. We measure Typhon's dynamical oblateness, $J_2$, at $\sim10σ$ confidence and find that Typhon's rotation pole is $\gtrsim20^\circ$ misaligned with the binary's mutual orbit. Assuming Typhon has a triaxial shape, our results, combined with rotational light curves and thermal measurements from the literature, suggest ellipsoidal semi-axes of $a=93^{+8}_{-6}$ km, $b=84^{+6}_{-6}$ km, and $c=65^{+9}_{-8}$ km. We further investigate the observational consequences of the complex spin-orbit dynamics, including light curve alteration by axial precession of Typhon and substantial changes to the system's mutual event season. Based on the system's dynamically excited state, we suggest a recent encounter with a giant planet may have substantially altered the system, potentially consistent with a binary in an early stage of disruption. This hypothesis can be tested with resolved photometric observations of the system. Our investigation highlights how non-Keplerian dynamics enhances our understanding of TNB systems and motivates ongoing observations of TNBs with astrometry, photometry, and stellar occultations.

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arXiv2026

Rotation and Mutual Eclipse Events Season in the Kuiper Belt: (524366) 2001 XR$_{254}$

(524366) 2001 XR$_{254}$ is a dynamically Cold Classical Kuiper Belt Object that is a nearly equal-sized wide binary whose upcoming mutual events season makes it a particularly valuable target for physical characterization. In advance of the mutual eclipse events, we conducted a ground-based photometric observing campaign between 2021 and 2026 using the \textit{Lowell Discovery Telescope} to investigate the rotational and physical properties of the system, to refine predictions for its future mutual events, as well as provide a lightcurve we can use as a baseline to identify eclipse events superimposed with the rotation. We derive a double-peaked asymmetric rotational lightcurve with a period of 11.17$\pm$0.04 h and a lightcurve amplitude of 0.42$\pm$0.04 mag. The lightcurve presents a sharp V-shaped minimum consistent with the primary being a close/contact binary, possibly making this a triple system. Using the Keplerian mutual orbit solution, we model the upcoming mutual event season expected between $\sim$2031 and $\sim$2040 and present some individual events for future campaigns. 2001 XR$_{254}$ is one of the few wide binary Kuiper belt systems with a well-determined mutual orbit and a soon observable mutual eclipse event season. Mutual event observations of this possible triple system will provide a rare opportunity to improve component sizes, shapes, densities, and surface properties, offering insights into the formation of the Kuiper Belt.

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arXiv2026

Kilometre-scale Jovian moon characterized for a potential JUICE flyby

Jupiter's irregular satellites are thought to be relics of early Solar System planetesimals. However, their small sizes, large distances from Earth and close angular proximity to Jupiter make them difficult to characterize remotely. Here we report multi-instrument observations of kilometre-sized Kallichore, the only irregular moon of Jupiter amenable to a close flyby by ESA's Jupiter Icy Moons Explorer (JUICE), whose astrometric and physical properties were still poorly constrained. We used Hubble photometry and astrometry, followed by a ground-based, multi-site stellar occultation campaign and astrometric and photometric observations with the 10.4-m Gran Telescopio Canarias. We reduced Kallichore's orbital uncertainty by up to approximately 80% and determined its shape: an elongated object with a minimum semi-axis ratio of a/b = 1.53 +/- 0.10, an area-equivalent diameter of 3.8 (+2.3/-0.3) km and a dark surface with a geometric albedo of 3.7% (+0.7/-2.2). No close companions were detected. These new constraints provide a viable pathway towards a JUICE flyby once the spacecraft arrives in the Jupiter system in 2031.

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arXiv2026

Triaxial shapes and densities of G!kún||'hòmdímà, Haumea, and Varda from stellar occultations

The shapes and densities of mid-sized and large trans-Neptunian objects (TNOs) are pivotal for understanding a variety of important aspects of planet formation. In this work, we present a Bayesian shape modeling method which combines constraints from rotational light curves and satellite orbits to construct three-dimensional shape models of TNOs. We use it to reanalyze three stellar occultations of the TNOs (229762) G!kún||'hòmdímà (2007 UK$_{126}$), (136108) Haumea, and (174567) Varda. By assuming that their satellites (or ring) orbit in their respective equatorial planes, we are able to derive unique shape models for both G!kún||'hòmdímà and Haumea. Our derived shape for G!kún||'hòmdímà is spheroidal with $a = b = 329^{+4}_{-3}$ km and $c = 294^{+11}_{-10}$ km, with a system density $ρ= 1007^{+50}_{-49}$ kg m$^{-3}$. For Haumea, we find $a = 1061^{+87}_{-71}$ km, $b = 844^{+5}_{-7}$ km, and $c = 514^{+18}_{-19}$ km, providing $ρ= 2050^{+157}_{-152}$ kg m$^{-3}$. For Varda, after updating its mutual orbit with its satellite Ilmarë, we find that currently published data are unable to fully constrain its three-dimensional shape. Intriguingly, Varda's elongated limb appears to point towards its satellite at the time of the occultation. With a $\sim$2\% chance of such an alignment happening randomly, this may be suggestive of a frozen-in tidal and/or rotational bulge. Our work emphasizes the importance of how external constraints can improve occultation analyses. With continued observations of rotational light curves, stellar occultations, and satellite orbits, these and other TNOs can have their shapes and densities further refined.

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arXiv2026

Trans-Neptunian Binary Mutual Events in the 2020s and 2030s

Mutual events of trans-Neptunian binaries (TNBs) provide rare opportunities to measure the physical and orbital properties of small bodies in the outer solar system. However, successful observations of these events have been limited by uncertain predictions. Here, we present probabilistic predictions of TNB mutual events occurring through the 2030s, using high-precision non-Keplerian orbit solutions from the Beyond Point Masses project combined with a Bayesian framework that propagates orbital and size uncertainties. Our methods generate distributions of event timing, duration, depth, and probability of occurrence, enabling direct assessment of observability. We provide predictions for five systems with ongoing or imminent mutual event seasons, including (38628) Huya, (58534) Logos-Zoe, (148780) Altjira, (469705) Kágára and !Hãunu, and (524366) 2001 XR$_{254}$. Preparing for upcoming events with long-baseline light curve monitoring is vital, as events may be difficult to distinguish from a regular rotational light curve. Rapid dissemination of event detections will benefit the entire community, allowing predictions to be updated, ensuring that these rare mutual event opportunities can be fully exploited.

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arXiv2025

Beyond Point Masses. V. Weywot's Non-Keplerian Orbit

We present a detailed dynamical analysis of the Quaoar-Weywot system based on nearly 20 years of high-precision astrometric data, including new HST observations and stellar occultations. Our study reveals that Weywot's orbit deviates significantly from a purely Keplerian model, requiring the inclusion of Quaoar's non-spherical gravitational field and center-of-body-center-of-light (COB-COL) offsets in our orbit models. We place a robust upper limit on Weywot's orbital eccentricity ($e<0.02$), substantially lower than previous estimates, which has important implications for the strength of mean motion resonances (MMRs) acting on Quaoar's ring system. Under the assumption that Quaoar's rings lie in its equatorial plane, we detect Quaoar's dynamical oblateness, $J_2$, at $\sim$2$σ$ confidence. The low $J_2$ value found under that assumption implies Quaoar is differentiated, with a total bulk density of $1751\pm13$ (stat.) kg m$^{-3}$. Additionally, we detect significant COB-COL offsets likely arising from latitudinal albedo variations across Quaoar's surface. These offsets are necessary to achieve a statistically robust orbit fit and highlight the importance of accounting for surface heterogeneity when modeling the orbits of dwarf planet moons. These findings improve our understanding of Quaoar's interior and surface while providing key insights into the stability and confinement mechanisms of its rings.

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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

Synchronous Rotation in the (120347) Salacia-Actaea System

We report on roughly 16 years of photometric monitoring of the transneptunian binary system (120347) Salacia-Actaea which provides significant evidence that Salacia and Actaea are tidally locked to the mutual orbital period in a fully synchronous configuration. The orbit of Actaea is updated, followed by a Lomb-Scargle periodogram analysis of the ground-based photometry which reveals a synodic period similar to the orbital period and a peak-to-peak lightcurve amplitude of δm = 0.0900 {\pm} 0.0036 mag (1σ uncertainty). Incorporating archival HST photometry that resolves each component, we argue that the periodicity in the unresolved data is driven by a longitudinally varying surface morphology on Salacia, and derive a sidereal rotation period that is within 1σ of the mutual orbital period. A rudimentary tidal evolution model is invoked that suggests synchronization occurred within 1.1 Gyr after Actaea was captured/formed.

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arXiv2025

Constraints on Quaoar's rings and atmosphere from JWST/NIRCam observations of a stellar occultation

Observations of stellar occultations have revealed that small bodies are capable of hosting ring systems. The trans-Neptunian object (TNO) Quaoar, is the host of an enigmatic ring system, with two rings located well-outside the Roche limit. To better understand these structures, we observed a stellar occultation by Quaoar and its rings using the James Webb Space Telescope's (JWST) NIRCam instrument. Our observations detect both known rings, although Q2R -- the inner known ring -- is not detected on both sides of Quaoar, showing that it has substantial azimuthal variations similar to Q1R -- the outer ring. We also fit a model of the ring radii and pole orientation of the ring system, which confirms that Quaoar's spin-orbit and Weywot's mean motion resonances (especially Weywot's 6:1) may play a role in the rings' confinement and stability. In addition to examination of Quaoar's ring system, we also use our observations to place upper limits on a putative CH$_4$ atmosphere around Quaoar, finding that no global atmosphere with surface pressure $>1$ nbar can exist (at 3$σ$ significance). The lack of atmosphere supports the hypothesis that atmospheric processes are not the source of Quaoar's recently discovered inventory of light hydrocarbons.

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arXiv2022

The formation of Haumea and its family via binary merging

Dozens of families of asteroids in the asteroid belt have similar orbits and compositions because they formed through a collision. However, the icy debris beyond the orbit of Neptune, called the Kuiper Belt, contains only one known family, the Haumea family. So far, no self-consistent explanation for the formation of the Haumea family can match all geophysical and orbital characteristics of the family without invoking extremely improbable events. Here, we show that the family is adequately explained as the product of a merging binary near the end of Neptune's orbital migration. The unique orbital signature of a merging binary, which was not found in extensive searches, is effectively erased during the final stages of migration, providing an explanation for all aspects of the Haumea family. By placing the formation of the Haumea family in the broader context of solar system formation, we demonstrate a proof-of-concept model for the formation of Haumea.

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arXiv2019

Modeling the Formation of the Family of the Dwarf Planet Haumea

The dwarf planet (136108) Haumea has an intriguing combination of unique physical properties: near-breakup spin, two regular satellites, and an unexpectedly compact family. While these properties indicate formation by collision, there is no self-consistent and reasonably probable formation hypothesis that can connect the unusually rapid spin and the low relative velocities of Haumea family members ("Haumeans"). We explore and test the proposed formation hypotheses (catastrophic collision, graze-and-merge, and satellite collision). We flexibly parameterize the properties of the collision (e.g., the collision location) and use simple models for the three-dimensional velocity ejection field expected from each model to generate simulated families. These are compared to observed Kuiper Belt Objects using Bayesian parameter inference, including a mixture model that allows for interlopers from the background population. After testing our methodology, we find the best match to the observed Haumeans is an isotropic ejection field with a typical velocity of 150 m s$^{-1}$. The graze-and-merge and satellite collision hypotheses are disfavored. Including these constraints, we discuss the formation hypotheses in detail, including variations, some of which are tested. Some new hypotheses are proposed (a cratering collision and a collision where Haumea's upper layers are "missing") and scrutinized. We do not identify a satisfactory formation hypothesis, but we do propose several avenues of additional investigation. In addition, we identify many new candidate Haumeans and dynamically confirm 7 of them as consistent with the observed family. We confirm that Haumeans have a shallow size distribution and discuss implications for the identification of new Haumeans.

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