Rosemary E. Pike

Weywot is the largest satellite of the candidate dwarf planet Quaoar, which also hosts a remarkable ring system located beyond its Roche limit—a configuration that challenges conventional understanding of ring dynamics. In this work, we predicted three stellar occultations by Weywot occurring in 2023 May and June, of which one was successfully observed on 2023 June 22. This multichord event took place over North America, where observers were deployed across the shadow path from Maryland to California. Five positive detections and two near misses allowed us to accurately constrain Weywot’s projected size and shape at the time of the occultation. We constrained the equivalent diameter to be between 116 and 172 km (with 95% confidence) and estimate a geometric albedo between 0.024 and 0.078—substantially lower than that of Quaoar. These results offer new insights into the physical properties of Quaoar’s system and provide valuable constraints for models of its formation and evolution.

The Colours of the Outer Solar System Origins Survey (Col-OSSOS) measured the optical/near-IR colors of a brightness-complete sample of trans-Neptunian objects (TNOs). Like previous surveys, this one found a bimodal color distribution in TNOs, categorized as red and very red. Additionally, this survey proposed an alternative surface classification scheme: FaintIR and BrightIR. Cold classical TNOs mostly have very red or FaintIR surfaces, while dynamically excited TNOs show a mixture of surfaces. This likely indicates that formation locations and proximity to the Sun influenced surface characteristics and color changes. Our study combines the data from Col-OSSOS with two dynamical models describing the formation of the Kuiper Belt during Neptune’s migration. We investigate the proposed surface-color-changing line and explore the distribution of different surfaces within the primordial disk. By comparing radial color transitions across various scenarios, we explore the origins of surface characteristics and their implications within the context of BrightIR and FaintIR classifications. Moreover, we extend our analysis to examine the distribution of these surface classes within the present-day Kuiper Belt, providing insights into the configuration of the early solar system’s planetesimal disk prior to giant planet migration. We find that the most likely primordial disk compositions are inner neutral/outer red (with transition 30 . 0 − 1.2 + 1.1 au) and inner BrightIR/outer FaintIR (with transition 31 . 5 − 1.2 + 1.1 au).

Manual review to select a reliable rotation period of small solar system bodies (SSSBs) is a very time-consuming process. With the growing volume of lightcurve data collected by wide-field, high-cadence surveys, such manual inspection has become impractical and unsustainable. In response to this challenge, we present a new algorithm, called the significance-convergence test, which provides a quantitative way to select reliable rotation periods of SSSBs obtained from these wide-field, high-cadence surveys. This algorithm was developed based on two simulations, each containing 162,000 synthetic lightcurves generated according to the observational conditions and data properties of the surveys from the phase I of the Formation of the Outer Solar System: an Icy Legacy (FOSSIL I) and Pan-STARRS 1 (PS1). Using two parameters extracted from period analysis, the successful recoveries of the input rotation periods from the synthetic lightcurves can be distinguished from unsuccessful recoveries and noisy lightcurves. The first parameter, 1/ S , indicates the significance of the best-fit spin rate, while the second parameter, C , represents the condition of convergence of the best-fit lightcurve. This algorithm can also be used as a mapping to the conventional quality code of manual review, U , defined by Warner et al. The significance-convergence test thus provides a practical alternative to manual review, which is a time-consuming and biased process.

Being one of the most populated mean motion resonances (MMRs) with Neptune and lying close to the inner boundary of the present-day cold classical disk, observations of the orbital and surface class distributions of the plutinos in the 3:2 MMR provide constraints on Neptune’s migration and insight into the compositional structure of the premigration planetesimal disk. Here, we present observations of the surface reflectance of 43 small to midsize (H _V ≳ 5) trans-Neptunian objects (TNOs) through the grz wavelength range, 14 of which are plutinos. We classify the surfaces of these TNOs using the two-surface class model (FaintIR and BrightIR surface classes) proposed by Fraser and collaborators, where the FaintIR surface class is dominated by cold classicals. Incorporating similar observations of plutinos from the literature for a total sample size of 43 plutinos, we find that the osculating inclination distributions (i _osc) of the FaintIR and BrightIR plutinos are statistically distinguishable at 99.3% significance, where six out of seven of the plutinos with i _osc < 4 . ° 5 have FaintIR surfaces. This is most easily explained if the FaintIR and BrightIR planetesimals were radially partitioned in the primordial planetesimal disk before being captured into the 3:2 resonance. While this could be evidence that the primordial cold classical disk with FaintIR surfaces was broader in the past by ∼3 au in the sunward direction, we cannot rule out the alternative explanation that these FaintIR plutinos were scattered from the ∼42.5–48 au region from the Sun and captured into the 3:2 resonance.

Being one of the most populated mean motion resonances (MMR) with Neptune and lying close to the inner boundary of the present day cold classical disk, observations of the orbital and surface class distributions of the plutinos in the 3:2 MMR provide constraints on Neptune's migration and insight into the compositional structure of the pre-migration planetesimal disk. Here, we present observations of the surface reflectance of 43 small to mid-size (H_V >~ 5) transneptunian objects (TNOs) through the grz wavelength range, 14 of which are plutinos. We classify the surfaces of these TNOs using the two-surface class model (FaintIR and BrightIR surface classes) proposed by Fraser and collaborators, where the FaintIR surface class is dominated by cold classicals. Incorporating similar observations of plutinos from the literature for a total sample size of 43 plutinos, we find that the osculating inclination distributions (i_osc) of the FaintIR and BrightIR plutinos are statistically distinguishable at 99.3% significance, where (6/7) of the plutinos with i_osc > 4.5° have FaintIR surfaces. This is most easily explained if the FaintIR and BrightIR planetesimals were radially partitioned in the primordial planetesimal disk before being captured into the 3:2 resonance. While this could be evidence that the primordial cold classical disk with FaintIR surfaces was broader in the past by ~3 au in the sunward direction, we cannot rule out the alternative explanation that these FaintIR plutinos were scattered from the ~42.5-48 au region from the Sun and captured into the 3:2 resonance.

In early solar system numerical simulations, where chaos is a primary driver, it is difficult to explore parameter space in a systematic way. In such simulations, stable configurations are hard to come by, and often require special fine-tuning. In addition, it is infeasible to run suites of well-resolved, realistic simulations with a disk of massive particles to drive planetary evolution where enough particles remain to represent the trans-Neptunian populations to robustly statistically compare with observations. To complement state-of-the-art full N-body simulations, we develop a method to artificially control each planet’s orbital elements independently from each other, which, when carefully applied, can be used to test a wider suite of models. We modify two widely used publicly available N-body integrators: (1) the C code, REBOUND, and (2) the FORTRAN code, Mercury6.2. We show how the application of specific fictitious forces within numerical integrators can be used to tightly control planetary evolution to more easily explore migration and orbital excitation and damping. This tool allows us to replicate the impact that a massive planetesimal disk would have on the planets, without actually including the massive planetesimals, thus decreasing the chaos and simulation runtime. We demonstrate the utility of this tool by applying it to the coupled orbital evolution of Uranus and Neptune, and show that Neptune’s eccentricity damping and radial outward migration have the appropriate affect on Uranus’ eccentricity.

The Large inclination Distant Objects (LiDO) survey has discovered the first securely classified object in the 10:1 mean motion resonance of Neptune. This object, 2020 VN₄₀, is short-term stable in the 10:1 resonance, but not stable on Gyr timescales. 2020 VN₄₀ is likely part of the scattering sticking population, and temporarily resides in the 10:1 resonance at ∼139.5 au. This discovery confirms that this distant resonance is populated, as a single detection is likely to be indicative of a large population that is difficult to detect due to observational biases. This object has an inclination of 33 . ° 4, and n-body integrations of orbital clones of 2020 VN₄₀ have revealed some unexpected evolutions. While clones of 2020 VN₄₀ show resonant libration around the expected resonance centers of approximately 90°, 180°, and 270°, for a restricted range of inclination and eccentricity values some clones librate around a resonant argument of 0°. As this occurs for the slightly lower-eccentricity portions of the evolution, this behavior can also be quite stable. Our initial exploration suggests that this libration around a center of 0° is a generic effect for highly inclined objects in n:1 resonances because the nature of their resonant interaction with Neptune becomes a strong function of their argument of pericenter, ω. At large inclination, the resonant islands shift as ω precesses, switching the center of symmetric libration to 0° for ω = 90° and ω = 270°. 2020 VN₄₀ provides interesting insight into the evolution of the large-inclination resonators, which become more common at increasing semimajor axes.

We present a publicly available, high-resolution, filled-parameter-space synthetic distribution of the plutinos, trans-Neptunian objects (TNOs) librating in the 3:2 mean-motion resonance with Neptune, with particular focus on the plutinos simultaneously Kozai librating. This synthetic distribution was built in preparation for results from the Large inclination Distant Objects (LiDO) survey, which pointed at locations on the sky where Kozai plutinos are predicted to come to pericenter and are thus most easily detected in magnitude-limited surveys. Although we do not expect the full stable parameter space presented here to be populated with real TNOs, it provides a useful starting point for comparison with Neptune migration simulations and debiased observational results. Our new stable parameter-space synthetic distribution of fictitious plutinos is consistent with previous works, and we build on past results by focusing on the behavior of Kozai plutinos over 4 Gyr integrations. We find that 95% of 4 Gyr stable Kozai plutinos remain in the same ω-libration island for the entire integration. This provides an interesting diagnostic opportunity: any asymmetry in the true number of 4 Gyr stable Kozai plutinos in the two ω-libration islands must be caused by the details of emplacement during giant planet migration. Through analysis of previously published Neptune migration models, we show that the intrinsic fraction of plutinos captured into Kozai depends on Neptune’s migration speed and mode. Combining the filled-parameter-space synthetic distribution with future migration simulations and the results of the carefully characterized LiDO survey will enable interpretation of the intrinsic orbital distribution of the Kozai and non-Kozai plutinos.