Outer Solar System Origins Survey Research Articles

Randomness and retention: using weak mean motion resonances to constrain Neptune’s late-stage migration

ABSTRACT Planet–planetesimal interactions cause a planet to migrate, manifesting as a random walk in semimajor axis. In models for Neptune’s migration involving a gravitational upheaval, this planetesimal-driven migration is a side-effect of the dynamical friction required to damp Neptune’s orbital eccentricity. This migration is noisy, potentially causing Trans-Neptunian Objects (TNOs) in mean motion resonance to be lost. With N-body simulations, we validate a previously derived analytic model for resonance retention and determine unknown coefficients. We identify the impact of random-walk (noisy) migration on resonance retention for resonances up to fourth order lying between 39 and 75 au. Using a population estimate for the weak 7:3 resonance from the well-characterized Outer Solar System Origins Survey (OSSOS), we rule out two cases: (1) a planetesimal disc distributed between 13.3 and 39.9 au with ≳ 30 Earth masses in today’s size distribution and Tmig ≳ 40 Myr and (2) a top-heavy size distribution with ≳2000 Pluto-sized TNOs and Tmig ≳10 Myr, where Tmig is Neptune’s migration time-scale. We find that low-eccentricity TNOs in the heavily populated 5:2 resonance are easily lost due to noisy migration. Improved observations of the low-eccentricity region of the 5:2 resonance and of weak mean motion resonances with Rubin Observatory’s Legacy Survey of Space and Time will provide better population estimates, allowing for comparison with our model’s retention fractions and providing strong evidence for or against Neptune’s random interactions with planetesimals.

Can Neptune’s Distant Mean Motion Resonances Constrain Undiscovered Planets in the Solar System? Lessons from a Case Study of the 9:1 Resonance

Recent observational surveys of the outer solar system provide evidence that Neptune's distant n:1 mean motion resonances may harbor relatively large reservoirs of trans-Neptunian objects (TNOs). In particular, the discovery of two securely classified 9:1 resonators, 2015 KE172 and 2007 TC434, by the Outer Solar System Origins Survey is consistent with a population of order 104 such objects in the 9:1 resonance with absolute magnitude H r < 8.66. This work investigates whether the long-term stability of such populations in Neptune’s n:1 resonances can be used to constrain the existence of distant 5–10 M ⊕ planets orbiting at hundreds of au. The existence of such a planet has been proposed to explain a reported clustering in the orbits of highly eccentric “extreme” trans-Neptunian objects (or eTNOs), although this hypothesis remains controversial. We engage in a focused computational case study of the 9:1 resonance, generating synthetic populations and integrating them for 1 Gyr in the presence of 81 different test planets with various masses, perihelion distances, eccentricities, and inclinations. While none of the tested planets are incompatible with the existence of 9:1 resonators, our integrations shed light on the character of the interaction between such planets and nearby n:1 resonances, and we use this knowledge to construct a simple heuristic method for determining whether or not a given planet could destabilize a given resonant population. We apply this method to the currently estimated properties of Planet 9, and find that a large primordial population in the 15:1 resonance (or beyond), if discovered in the future, could potentially constrain the existence of this planet.

Outcomes of Contemporary Novel Agent and Stem Cell Transplantation in Relapsed/Refractory PTCL

Background Outcomes in relapsed/refractory (R/R) peripheral T-cell lymphoma (PTCL) continue to be suboptimal. In the last decade, several novel agents have been approved; however, their impact on survival remains to be defined. In this multi-center retrospective analysis, we assessed survival following initial progression with respect to novel agent exposure with and without the use of stem cell transplant (SCT). Methods Patients with PTCL diagnosed between 1998-2021 at New York Presbyterian Hospitals, Columbia and Cornell, were included after IRB approval. Medical records were reviewed for baseline characteristics and treatment parameters. In the second line setting, each patient fell into one of four categories: 1. novel agent containing regimen only ( novel-containing only), 2. novel agent containing regimen with SCT at end of second line ( novel + SCT), 3. chemotherapy alone ( chemo-only), and 4. chemotherapy with SCT at end of second line ( chemo + SCT). Event-free survival (EFS) was calculated as time from 1 st progression to 2 nd progression, re-treatment, or death. Subsequent OS (sOS) was calculated from date of first progression to death or last follow-up. Kaplan-Meier method was used to estimate survival probability. Survival difference was tested by log-rank and Cox regression analysis. Results A total of 348 patients with PTCL were identified, of which 189 had R/R disease and 184 had sufficient data for analysis. The median follow-up was 62.5m. Baseline characteristics are shown in Table 1. Most common PTCL subtypes were AITL (N=52, 28.3%), PTCL-NOS (N=39, 21.2%), ATLL (N=34, 18.5%), and ALCL (ALK- = 13, ALK+ = 11, n=24, 13%). Median age at diagnosis was 58 years. Median EFS and sOS from date of initial progression for the entire cohort was 5.0m and 25.1m, respectively. In the second-line setting, 92 (50%) received a novel-containing only, 62 (34%) patients received chemo-only, 17 (9%) received chemo + SCT, and 13 (7%) received novel + SCT. Median EFS from first progression among patients who received second-line novel + SCT was 16.0m (95% CI 6.0 - NR), chemo + SCT 15.0m (95% CI 6.2 - 24.5), novel-containing only 3.9m (95% CI 3.5 - 5.3), and chemo-only 4.1m (95% CI 2.9 - 5.1) as shown in Figure 1. Two-year EFS favored novel + SCT at 38.5m (95% CI 12.0 - 64.9) and chemo + SCT 34.0m (95% CI 10.8 - 57.1), compared to novel-containing only at 18.3m (95% CI 10.1 - 26.6) and chemo-only 11.3m (95% CI 3.0 - 19.6), with p &amp;lt; 0.001 across all groups. Median sOS among patients who received second-line novel + SCT was 70.7m (95% CI 16.0 - NR), chemo + SCT not reached (95% CI 15.0 - NR), novel-containing only 23.3m (95% CI 10.5 - NR), and chemo-only 16.7m (95% CI 11.7 - 27.0). Two-year sOS favored novel + SCT at 74.6m (95% CI 49.7 - 99.5) and chemo + SCT 70.4m (95% CI 48.5 - 92.2) compared to novel-containing only at 49.4m (95% CI 37.9 -61.0) and chemo-only 43.4m (95% CI 30.0 - 56.9), with p =0.014 across all groups. Conclusion This multi-center study represents one of the largest retrospective R/R PTCL cohorts in the modern era with sOS of 25.1m, which compares favorably to historical data collected a decade ago reporting a sOS of 5.5m in R/R patients receiving chemo-only (Mak 2013), however, compares similarly to more recent data from the COMPLETE study (Lansigan 2019). This improvement in sOS may reflect availability of more effective therapies for sequencing in the novel agent era. Our data suggests that SCT in second-line setting is associated with improved EFS and sOS for both those treated with novel agent containing regimens and chemotherapy. Differences are more prominent for two-year EFS and sOS, favoring SCT arms and novel agents. However, the retrospective nature of our data limits definitive conclusion of benefit derived from SCT in the second-line setting, which underscores the need for prospective studies in this area. *This work has been funded ASH RTAF

Col-OSSOS: The Distribution of Surface Classes in Neptune's Resonances

The distribution of surface classes of resonant trans-Neptunian objects (TNOs) provides constraints on the protoplanetesimal disk and giant planet migration. To better understand the surfaces of TNOs, the Colours of the Outer Solar System Origins Survey acquired multiband photometry of 102 TNOs and found that the surfaces of TNOs can be well described by two surface classifications: BrightIR and FaintIR. These classifications both include optically red members and are differentiated predominantly based on whether their near-infrared spectral slope is similar to their optical spectral slope. The vast majority of cold classical TNOs, with dynamically quiescent orbits, have the FaintIR surface classification, and we infer that TNOs in other dynamical classifications with FaintIR surfaces share a common origin with the cold classical TNOs. Comparison between the resonant populations and the possible parent populations of cold classical and dynamically excited TNOs reveal that the 3:2 has minimal contributions from the FaintIR class, which could be explained by the ν 8 secular resonance clearing the region near the 3:2 before any sweeping capture occurred. Conversely, the fraction of FaintIR objects in the 4:3 resonance, 2:1 resonance, and the resonances within the cold classical belt suggest that the FaintIR surface formed in the protoplanetary disk between ≳34.6 and ≲47 au, though the outer bound depends on the degree of resonance sweeping during migration. The presence and absence of the FaintIR surfaces in Neptune’s resonances provides critical constraints for the history of Neptune’s migration, the evolution of the ν 8, and the surface class distribution in the initial planetesimal disk.

Col-OSSOS: Evidence for a Compositional Gradient Inherited from the Protoplanetary Disk?

In the present-day Kuiper Belt, the number of compositional classes and the orbital distributions of these classes hold important cosmogonic implications for the solar system. The Colours of the Outer Solar System Origins Survey (Col-OSSOS) recently showed that the observed color distribution of small (H ⪆ 6) trans-Neptunian objects (TNOs) can be accounted for by the existence of only two composition classes, named BrightIR and FaintIR, where the range of colors in each class can be modeled as mixtures of two material end-members. Here, we combine the high-precision photometric measurements of Col-OSSOS with those of previous surveys to investigate the orbital distribution of the two color classes and reinterpret the known color–inclination correlation of TNOs in the context of the BrightIR/FaintIR taxonomy. In addition to confirming the previously reported distinct orbital distributions of these classes, we identify a trend of increasing orbital inclinations toward the bluer end of the optical and near-infrared color distribution of BrightIR objects. Using the output of numerical simulations investigating the orbital evolution of TNOs during their scattering phase with Neptune, we show that this trend could reflect a composition gradient in the early protoplanetary disk, in the range of heliocentric distances over which TNOs from the BrightIR class accreted. However, tensions between this interpretation and the existence of blue contaminants among cold classical TNOs, and possible alternative origins for the detected correlation, currently bear uncertainty on our proposed interpretation.

Is There an Earth-like Planet in the Distant Kuiper Belt?

The orbits of trans-Neptunian objects (TNOs) can indicate the existence of an undiscovered planet in the outer solar system. Here we used N-body computer simulations to investigate the effects of a hypothetical Kuiper Belt planet (KBP) on the orbital structure of TNOs in the distant Kuiper Belt beyond ∼50 au. We used observations to constrain model results, including the well-characterized Outer Solar System Origins Survey (OSSOS). We determined that an Earth-like planet (m ∼ 1.5–3 M ⊕) located on a distant (semimajor axis a ∼ 250–500 au, perihelion q ∼ 200 au) and inclined (i ∼ 30°) orbit can explain three fundamental properties of the distant Kuiper Belt: a prominent population of TNOs with orbits beyond Neptune’s gravitational influence (i.e., detached objects with q > 40 au), a significant population of high-i objects (i > 45°), and the existence of some extreme objects with peculiar orbits (e.g., Sedna). Furthermore, the proposed KBP is compatible with the existence of identified gigayear-stable TNOs in the 2:1, 5:2, 3:1, 4:1, 5:1, and 6:1 Neptunian mean motion resonances. These stable populations are often neglected in other studies. We predict the existence of an Earth-like planet and several TNOs on peculiar orbits in the outer solar system, which can serve as observationally testable signatures of the putative planet’s perturbations.

OSSOS. XXIX. The Population and Perihelion Distribution of the Detached Kuiper Belt

The detached trans-Neptunian objects (TNOs) are those with semimajor axes beyond the 2:1 resonance with Neptune that are neither resonant nor scattering. Using the detached sample from the Outer Solar System Origins Survey (OSSOS) telescopic survey, we produce the first studies of their orbital distribution based on matching the orbits and numbers of the known TNOs after accounting for survey biases. We show that the detached TNO perihelion (q) distribution cannot be uniform but is instead better matched by two uniform components with a break near q ≈ 40 au. We produce parametric two-component models that are not rejectable by the OSSOS data set and estimate that there are 36,000 detached TNOs with absolute magnitudes H r < 8.66 (D ≳ 100 km) and semimajor axes 48 au < a < 250 au (95% confidence limits). Although we believe that these heuristic two-parameter models yield a correct population estimate, we then use the same methods to show that the perihelion distribution of a detached disk created by a simulated rogue planet matches the q distribution even better, suggesting that the temporary presence of other planets in the early solar system is a promising model to create today’s large semimajor axis TNO population. This cosmogonic simulation results in a detached TNO population estimate of 48,000. Because this illustrates how difficult-to-detect q > 50 au objects are likely present, we conclude that there are (5 ± 2) × 104 dynamically detached TNOs, roughly twice as many as in the entire trans-Neptunian hot main belt.

OSSOS. XXVII. Population Estimates for Theoretically Stable Centaurs between Uranus and Neptune

We calculate the upper bounds of the population of theoretically stable Centaur orbits between Uranus and Neptune. These small bodies are on low-eccentricity, low-inclination orbits in two specific bands of semimajor axis, centered at ∼24.6 and ∼25.6 au. They exhibit unusually long Gyr-stable lifetimes in previously published numerical integrations, orders of magnitude longer than that of a typical Centaur. Despite the increased breadth and depth of recent Solar System surveys, no such objects have been found. Using the Outer Solar System Origins Survey simulator to calculate the detection efficiency for these objects in an ensemble of fully characterized surveys, we determine that a population of 72 stable Centaurs with absolute magnitude H r ≤ 10 (95% confidence upper limit) could remain undetected. The upcoming Legacy Survey of Space and Time will be able to detect this entire intrinsic population, due to its complete coverage of the ecliptic plane. If detected, these objects will be interesting dynamically accessible mission targets—especially as comparison of the stable Centaur orbital phase space to the outcomes of several modern planetary migration simulations suggests that these objects could be close to primordial in nature.

Outcomes of contemporary novel agent incorporation in relapsed/refractory PTCL

Background: Conventional salvage chemotherapy has limited efficacy in relapsed/refractory (R/R) peripheral T-cell lymphoma (PTCL). In the last decade, several novel agents have been approved; however, their impact on real world survival remains to be defined. In this multi-center retrospective analysis, we assessed survival following initial progression with respect to novel agent exposure in patients who did not receive stem cell transplant (SCT). Methods: Patients with PTCL from 1998 to 2021 at Columbia and Cornell were included after IRB approval. Medical records were reviewed for baseline characteristics, treatment including (1) novel agents, (2) chemotherapy, and (3) auto- and/or allo-SCT across all lines of therapy. Event-free survival (EFS) was calculated as time from 1st progression to 2nd progression, re-treatment, or death. Subsequent OS (sOS) was calculated from date of first progression to death or last follow-up. Kaplan-Meier method was used to estimate survival probability. Survival difference was tested by log-rank and Cox regression analysis. Results: A total of 348 patients with PTCL were identified, of which 189 had R/R disease and 156 had sufficient data for analysis. The median follow-up was 45.4 m from 1st progression. Baseline characteristics are shown in Figure 1A. The major PTCL subtypes were AITL (N = 52, 27%), PTCL-NOS (N = 41, 21.7%), ATLL (N = 33, 17.5%), and ALCL (N = 23, 12.2%). Median age at diagnosis was 58. Following initial progression, 21 (11.1%) received auto-SCT, and 42 (22.2%) received allo-SCT in second or later lines. Out of those patients who did not undergo SCT (n = 93), 66 (70.9%) received novel-agent-containing regimen only and 27 (29%) received chemo-only in second and later lines. Median sOS from date of initial progression for the entire cohort was 21.3 m. In patients who did not receive SCT, sOS for chemo-only versus novel-agent-containing regimen only was 4.9 m versus 13.0 m, respectively (p = 0.132) with hazard ratio 0.66 (95% CI: 0.39–1.14, p = 0.1349), illustrated in Figure 1B. EFS from first progression in novel-agent-containing regimen only was 4.2 m versus chemo-only 3.6 m (p = 0.6131) with hazard ratio 0.88 (95% CI: 0.54–1.44, p = 0.6137). Keywords: Aggressive T-cell non-Hodgkin lymphoma, Molecular Targeted Therapies Conflicts of interests pertinent to the abstract. M. R. Seshadri Consultant or advisory role: Consulting for Gilead and Beigene Research funding: Research support from Roche and Eli Lilly

Col-OSSOS: The Two Types of Kuiper Belt Surfaces

The Colors of the Outer Solar System Origins Survey (Col-OSSOS) has gathered a high-quality, near-simultaneous, and brightness-complete sample of (g − r) and (r − J) colors for 102 Kuiper Belt objects (KBOs) with (u − g) and (r − z) gathered for some. We present the current state of the survey and data analysis. Recognizing that the optical colors of most icy bodies broadly follow the reddening curve, we present a new projection of the optical−near-IR (NIR) colors, which rectifies the main nonlinear features in the optical−NIR along the ordinates. We find evidence for a bifurcation in the projected colors that presents itself as a diagonal empty region in the optical−NIR. A reanalysis of past color surveys reveals the same bifurcation. We interpret this as evidence for two separate surface classes: the BrightIR class spans the full range of optical colors and broadly follows the reddening curve, while the FaintIR objects are limited in optical color and are less bright in the NIR than the BrightIR objects. We present a two-class model. Objects in each class consist of a mix of separate blue and red materials and span a broad range in color. Spectra are modeled as linear optical and NIR spectra with different slopes that intersect at some transition wavelength. The underlying spectral properties of the two classes reproduce the main observed structures in the UV−optical−NIR color space (0.4 μm ≲ λ ≲ 1.4 μm), including the bifurcation observed in the Col-OSSOS and H/WTSOSS data sets, including the tendency for cold classical KBOs to have lower (r − z) colors than excited objects, and the well-known bimodal optical color distribution.

The Hot Main Kuiper Belt Size Distribution from OSSOS

Using the absolute detection calibration and abundant detections of the Outer Solar System Origins Survey project, we provide population measurements for the main Kuiper Belt. For absolute magnitude H r < 8.3, there are 30,000 nonresonant main-belt objects, with twice as many hot-component objects than cold, and with total mass of 0.014 M ⊕, only one-seventh of which is in the cold belt (assuming a cold-object albedo about half that of hot-component objects). We show that trans-Neptunian objects with 5.5 < H r < 8.3 (rough diameters 400–100 km) have indistinguishable absolute magnitude (size) distributions, regardless of being in the cold classical Kuiper Belt (thought to be primordial) or the “hot” population (believed to be implanted after having been formed elsewhere). We discuss how this result was not apparent in previous examinations of the size distribution due to the complications of fitting assumed power-law functional forms to the detections at differing depths. This shared size distribution is surprising in light of the common paradigm that the hot-population planetesimals formed in a higher density environment much closer to the Sun, in an environment that also (probably later) formed larger (dwarf planet and bigger) objects. If this paradigm is correct, our result implies that planetesimal formation was relatively insensitive to the local disk conditions and that the subsequent planet-building process in the hot population did not modify the shape of the planetesimal size distribution in this 50–300 km range.

OSSOS XXV: Large Populations and Scattering–Sticking in the Distant Trans-Neptunian Resonances

There have been 77 TNOs discovered to be librating in the distant trans-Neptunian resonances (beyond the 2:1 resonance, at semimajor axes greater than 47.7 au) in four well-characterized surveys: the Outer Solar System Origins Survey (OSSOS) and three similar prior surveys. Here, we use the OSSOS Survey Simulator to measure their intrinsic orbital distributions using an empirical parameterized model. Because many of the resonances had only one or very few detections, j:k resonant objects were grouped by k in order to have a better basis for comparison between models and reality. We also use the Survey Simulator to constrain their absolute populations, finding that they are much larger than predicted by any published Neptune migration model to date; we also find population ratios that are inconsistent with published models, presenting a challenge for future Kuiper Belt emplacement models. The estimated population ratios between these resonances are largely consistent with scattering–sticking predictions, though further discoveries of resonant TNOs with high-precision orbits will be needed to determine whether scattering–sticking can explain the entire distant resonant population or not.

Col-OSSOS: Probing Ice Line/Color Transitions within the Kuiper Belt’s Progenitor Populations

Abstract Dynamically excited objects within the Kuiper Belt show a bimodal distribution in their surface colors, and these differing surface colors may be a tracer of where these objects formed. In this work, we explore radial color distributions in the primordial planetesimal disk and implications for the positions of ice line/color transitions within the Kuiper Belt’s progenitor populations. We combine a full dynamical model of the Kuiper Belt’s evolution due to Neptune’s migration with precise surface colors measured by the Colours of the Outer Solar System Origins Survey in order to examine the true color ratios within the Kuiper Belt and the ice lines within the primordial disk. We investigate the position of a dominant, surface color–changing ice line, with two possible surface color layouts within the initial disk: (1) inner neutral surfaces and outer red and (2) inner red surfaces and outer neutral. We performed simulations with a primordial disk that truncates at 30 au. By radially stepping the color transition out through 0.5 au intervals, we show that both disk configurations are consistent with the observed color fraction. For an inner neutral, outer red primordial disk, we find that the color transition can be at 28 − 3 + 2 au at a 95% confidence level. For an inner red, outer neutral primordial disk, the color transition can be at 27 − 3 + 3 au at a 95% confidence level.

OSSOS Finds an Exponential Cutoff in the Size Distribution of the Cold Classical Kuiper Belt

Abstract The cold main classical Kuiper Belt consists of the nonresonant small solar system bodies with low orbital inclinations and orbital semimajor axes between 42.4 and 47.7 au. These objects likely formed in situ, and the population has experienced minimal collisional modification since formation. Using the Outer Solar System Origins Survey ensemble sample and characterization, combined with constraints from deeper surveys and supported by evidence from the Minor Planet Center catalog and the Deep Ecliptic Survey, we determine the absolute magnitude H r distribution of the cold classical belt from H r ≃ 5 to 12 (roughly diameters of 400–20 km). We conclude that the cold population’s H r distribution exhibits an exponential cutoff at large sizes. Exponential cutoffs at large sizes are not a natural outcome of pairwise particle accretion, but exponentially tapered power-law size distributions are a feature of numerical simulations of planetesimal formation via a streaming instability. Our observation of an exponential cutoff agrees with previous observational inferences that no large objects (D ≳ 400 km) exist in the cold population. We note that the asymptotic slope of the H r distribution is consistent with α ∼ 0.4. This asymptotic slope is also found in streaming instability modeling of planetesimal formation and is thus not necessarily associated with achieving collisional equilibrium. Studies of the trans-Neptunian region are providing the parameters that will enable future streaming-instability studies to determine the initial conditions of planetesimal formation in the ≈45 au region of the Sun’s protoplanetary disk.

OSSOS. XXIII. 2013 VZ70 and the Temporary Coorbitals of the Giant Planets

Abstract We present the discovery of 2013 VZ70, the first known horseshoe coorbital companion of Saturn. Observed by the Outer Solar System Origins Survey for 4.5 yr, the orbit of 2013 VZ70 is determined to high precision, revealing that it currently is in “horseshoe” libration with the planet. This coorbital motion will last at least thousands of years but ends ∼10 kyr from now; 2013 VZ70 is thus another example of the already-known “transient coorbital” populations of the giant planets, with this being the first known prograde example for Saturn (temporary retrograde coorbitals are known for Jupiter and Saturn). We present a theoretical steady-state model of the scattering population of trans-Neptunian origin in the giant planet region (2–34 au), including the temporary coorbital populations of the four giant planets. We expose this model to observational biases using survey simulations in order to compare the model to the real detections made by a set of well-characterized outer solar system surveys. While the observed number of coorbitals relative to the scattering population is higher than predicted, we show that the number of observed transient coorbitals of each giant planet relative to each other is consistent with a trans-Neptunian source.

Col-OSSOS: The Distinct Color Distribution of Single and Binary Cold Classical KBOs

Abstract The cold classical Kuiper Belt Objects (KBOs) possess a high, ≳30% binary fraction. Widely separated and dynamically fragile, these binary systems have been useful in tracing the origins of KBOs. A new class of binaries was recently identified by their colors. The so-called blue binaries are unanimously members of the less red compositional class, and exhibit a 100% binary fraction. They appear to be push-out survivors, emplaced in the classical region during Neptune’s phases of outward migration. The presence of these binary systems implies that the majority of objects that formed near the cold classical region formed as binaries. Here we present new optical color measurements of cold classical KBOs from the Colors of the Outer Solar System Origins Survey, including colors of a blue binary discovered by the Solar System Origins Legacy Survey—2015 RJ277. The increased size of the colors sample has resulted in order-of-magnitude decrease in the probability that the binaries and singles sample share the same color distribution. From the Anderson–Darling statistic, this probability is only a 0.3%, while it is only 0.002% when utilizing the difference of means statistic. We find a hint that the blue binaries have inflated free inclinations compared to their red counterparts, consistent with the push-out origin for these bodies.

OSSOS. XXI. Collision Probabilities in the Edgeworth–Kuiper Belt

Abstract Here, we present results on the intrinsic collision probabilities, P I , and range of collision speeds, V I , as a function of the heliocentric distance, r, in the trans-Neptunian region. The collision speed is one of the parameters that serves as a proxy for a collisional outcome (e.g., disruption and scattering of fragments, or formation of a crater, as both processes are related to the impact energy). We utilize an improved and debiased model of the trans-Neptunian object (TNO) region from the “Outer Solar System Origins Survey” (OSSOS). It provides a well-defined model of TNO orbital distribution, based on multiple opposition observations of more than 1000 bodies. We compute collisional probabilities for the OSSOS models of the main classical, resonant, detached+outer, and scattering TNO populations. The intrinsic collision probabilities and collision speeds are computed using Öpik’s approach, as revised and modified by Wetherill for noncircular and inclined orbits. The calculations are carried out for each of the dynamical TNO groups, allowing for inter-population collisions as well as collisions within each TNO population, resulting in 28 combinations in total. Our results indicate that collisions in the trans-Neptunian region are possible over a wide range in (r, V I ) phase space. Although collisions are calculated to happen within r ∼ 20–200 au and V I ∼ 0.1 km s−1 to as high as V I ∼ 9 km s−1, most of the collisions are likely to happen at low relative velocities V I &lt; 1 km s−1 and are dominated by the main classical belt.

No Evidence for Orbital Clustering in the Extreme Trans-Neptunian Objects

Abstract The apparent clustering in longitude of perihelion ϖ and ascending node Ω of extreme trans-Neptunian objects (ETNOs) has been attributed to the gravitational effects of an unseen 5–10 Earth-mass planet in the outer solar system. To investigate how selection bias may contribute to this clustering, we consider 14 ETNOs discovered by the Dark Energy Survey, the Outer Solar System Origins Survey, and the survey of Sheppard and Trujillo. Using each survey's published pointing history, depth, and TNO tracking selections, we calculate the joint probability that these objects are consistent with an underlying parent population with uniform distributions in ϖ and Ω. We find that the mean scaled longitude of perihelion and orbital poles of the detected ETNOs are consistent with a uniform population at a level between 17% and 94% and thus conclude that this sample provides no evidence for angular clustering.

OSSOS: The eccentricity and inclination distributions of the stable neptunian Trojans

The minor planets on orbits that are dynamically stable in Neptune’s 1:1 resonance on Gyr timescales were likely em:laced by Neptune’s outward migration. We explore the intrinsic libration amplitude, eccentricity, and inclination distribution of Neptune’s stable Trojans, using the detections and survey efficiency of the Outer Solar System Origins Survey (OSSOS) and Pan-STARRS1. We find that the libration amplitude of the stable Neptunian Trojan population can be well modeled as a Rayleigh distribution with a libration amplitude width σAϕ of 15°. When taken as a whole, the Neptune Trojan population can be acceptably modeled with a Rayleigh eccentricity distribution of width σe of 0.045 and a typical sin(i) × Gaussian inclination distribution with a width σi of 14±2∘; however, these distributions are only marginally acceptable. This is likely because, even after accounting for survey detection biases, the known large (Hr<8) and small (Hr≥8) Neptune Trojans appear to have markedly different eccentricities and inclinations. We propose that like the classical Kuiper belt, the stable intrinsic Neptunian Trojan population have dynamically ‘hot’ and dynamically ‘cold’ components to its eccentricity/inclination distribution, with σe−cold∼0.02/σi−cold∼6° and σe−hot∼0.05/σi−hot∼18°. In this scenario, the ‘cold’ L4 Neptunian Trojan population lacks the Hr≥8.0 members and has 13−6+11 ‘cold’ Trojans with Hr<8.0. On the other hand, the ‘hot’ L4 Neptunian Trojan population has 136−75+84 Trojans with Hr<10 — a population 2.4 times greater than that of the L4 Jovian Trojans in the same luminosity range.

A statistical review of light curves and the prevalence of contact binaries in the Kuiper Belt

We investigate what can be learned about a population of distant Kuiper Belt Objects (KBOs) by studying the statistical properties of their light curves. Whereas others have successfully inferred the properties of individual, highly variable KBOs, we show that the fraction of KBOs with low amplitudes also provides fundamental information about a population. Each light curve is primarily the result of two factors: shape and orientation. We consider contact binaries and ellipsoidal shapes, with and without flattening. After developing the mathematical framework, we apply it to the existing body of KBO light curve data. Principal conclusions are as follows. (1) When using absolute magnitude H as a proxy for the sizes of KBOs, it is more accurate to use the maximum of the light curve (minimum H) rather than the mean. (2) Previous investigators have noted that smaller KBOs tend to have higher-amplitude light curves, and have interpreted this as evidence that they are systematically more irregular in shape than larger KBOs; we show that a population of flattened bodies with uniform proportions, independent of size, could also explain this result. (3) Our method of analysis indicates that prior assessments of the fraction of contact binaries in the Kuiper Belt may be artificially low. (4) The pole orientations of some KBOs can be inferred from observed changes in their light curves over time scales of decades; however, we show that these KBOs constitute a biased sample, whose pole orientations are not representative of the population overall. (5) Although surface topography, albedo patterns, limb darkening, and other surface properties can affect individual light curves, they do not have a strong influence on the statistics overall. (6) Photometry from the Outer Solar System Origins Survey (OSSOS) survey is incompatible with previous results and its statistical properties defy easy interpretation. We also discuss the promise of this approach for the analysis of future, much larger data sets such as the one anticipated from the upcoming Vera C. Rubin Observatory.