Samantha M. Lawler

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).

With a new probabilistic technique for sampling interstellar object (ISO) orbits with high efficiency, we assess the observability of ISOs under a realistic cadence for the upcoming Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST). Using the Ōtautahi–Oxford population model, we show that there will be complex on-sky structure in the pattern of direction and velocity revealed by the detected ISO population, with the expected enhanced northern flux complicating efforts to derive population parameters from the LSST’s predominately southern footprint. For reasonable luminosity functions with slopes of 2.5 ≤ q _s ≤ 4.0, the most discoverable ISOs have H _r ≃ 14.6−20.7. The slope of the luminosity function of ISOs will be relatively quickly constrained by the characteristics of the LSST detected population, such as the distributions of perihelia, velocity at infinity, and discovery circumstances. Discoveries are evenly split around their perihelion passage and are biased to lower velocities. After their discovery by LSST, it will be rare for ISOs to be visible for less than a month; most will have m _r ≤ 23 for months, and the window for spectroscopic characterization could be as long as 2 yr. While these probabilistic assessments are robust against model or spatial density refinements that change the absolute numbers of ISO discoveries, our simulations predict a yield of 6–51 asteroidal ISOs, which is similar to previous works and demonstrates the validity of our new methods.

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.

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 degrees, 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 degrees, for a restricted range of inclination and eccentricity values some clones librate around a resonant argument of 0 degrees. 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 degrees 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, omega. At large inclination, the resonant islands shift as omega precesses, switching the center of symmetric libration to 0 degrees for omega=90 degrees and omega=270 degrees. 2020 VN40 provides interesting insight into the evolution of the large-inclination resonators, which become more common at increasing semi-major axis.

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.

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.

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 4Gyr integrations. We find that 95% of 4Gyr stable Kozai Plutinos remain in the same omega-libration island for the entire integration. This provides an interesting diagnostic opportunity: any asymmetry in the true number of 4Gyr stable Kozai Plutinos in the two omega-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.