ORCID Profile
0000-0003-4143-8589
Current Organisations
Harvard-Smithsonian Center for Astrophysics
,
Smithsonian Institution
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Publisher: American Astronomical Society
Date: 04-2023
Abstract: 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.
Publisher: American Astronomical Society
Date: 02-07-2019
Publisher: American Astronomical Society
Date: 04-02-2019
Publisher: American Astronomical Society
Date: 05-06-2019
Publisher: Frontiers Media SA
Date: 16-05-2018
Publisher: American Astronomical Society
Date: 04-09-2019
Publisher: American Astronomical Society
Date: 18-08-2017
Publisher: Elsevier BV
Date: 06-2021
Publisher: American Astronomical Society
Date: 06-2018
Publisher: American Astronomical Society
Date: 11-2019
Publisher: EDP Sciences
Date: 2019
DOI: 10.1051/0004-6361/201834021
Abstract: Context. Centaurs are icy objects in transition between the trans-Neptunian region and the inner solar system, orbiting the Sun in the giant planet region. Some centaurs display cometary activity, which cannot be sustained by the sublimation of water ice in this part of the solar system, and has been hypothesized to be due to the crystallization of amorphous water ice. Aims. In this work, we investigate centaurs discovered by the Outer Solar System Origins Survey (OSSOS) and search for cometary activity. Tentative detections would improve understanding of the origins of activity among these objects. Methods. We search for comae and structures by fitting and subtracting both point spread functions and trailed point-spread functions from the OSSOS images of each centaur. When available, Col-OSSOS images were used to search also for comae. Results. No cometary activity is detected in the OSSOS s le. We track the recent orbital evolution of each new centaur to confirm that none would actually be predicted to be active, and we provide size estimates for the objects. Conclusions. The addition of 20 OSSOS objects to the population of ~250 known centaurs is consistent with the currently understood scenario, in which drastic drops in perihelion distance induce changes in the thermal balance prone to trigger cometary activity in the giant planet region.
Publisher: Copernicus GmbH
Date: 23-09-2022
DOI: 10.5194/EPSC2022-936
Abstract: & & Beyond the orbit of Neptune lies a sea of small icy bodies known as the Kuiper belt. The surfaces of these Kuiper Belt Objects (KBOs) have remained relatively unprocessed since their formation as a consequence of their distance from the Sun. This means that we can investigate their formation conditions in the early Solar System by studying their surfaces today. Generally, the small and most numerous KBOs are quite dim (r mag & 22), and so it is difficult to study their surfaces spectroscopically. Instead, we can use broadband photometry to take effectively very low-resolution spectra of their surfaces.& & & & When studied spectroscopically, the surfaces of smaller KBOs have generally shown very flat and featureless spectra within certain wavelength ranges. This means that broadband photometry (within those wavelength ranges) can reveal enough information to characterise the optical and near-infrared spectral slopes of these planetesimals. The Colours of the Outer Solar System Origins Survey (Col-OSSOS) has obtained optical and near-infrared broadband photometry of a s le of 92 KBOs, at unprecedented precision (~ & #177 .03 mag in optical wavelengths). These broadband surface colours allow small, dynamically excited KBOs to be characterised into a bimodal colour distribution (as with previous colour surveys), along with the identification of potentially outlying surface colours.& & & & As a side effect of Col-OSSOS& #8217 s observing technique we have a s le of objects with repeated optical colours, and some repeated near-infrared colours. We also have taken additional optical photometry of a small s le of KBOs with outlying surface colours. This allows us to investigate the possibility of photometric variation across multiple epochs for this s le of objects. Col-OSSOS observed sequential broadband filters on timescales less than the typical periods of small KBOs. Therefore, we can simultaneously fit a linear lightcurve and photometric colours to our photometry and potentially rule out lightcurve effects causing photometric variations. This means that differing colours across multiple epochs implies either differing surface composition, or that our approximation of linear brightness variability across the observing sequence is invalidated. We will present this s le and discuss implications for the spectrovariable population within the Kuiper belt.& &
Publisher: American Astronomical Society
Date: 08-07-2019
Publisher: American Astronomical Society
Date: 06-05-2021
DOI: 10.3847/PSJ/ABF04A
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 s le has resulted in order-of-magnitude decrease in the probability that the binaries and singles s le 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.
Publisher: American Astronomical Society
Date: 05-2022
DOI: 10.3847/PSJ/AC67E0
Abstract: 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.
Publisher: American Astronomical Society
Date: 05-2023
DOI: 10.3847/PSJ/ACC844
Abstract: The Colors of the Outer Solar System Origins Survey (Col-OSSOS) has gathered a high-quality, near-simultaneous, and brightness-complete s le 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 μ m ≲ λ ≲ 1.4 μ m), 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.
Publisher: American Astronomical Society
Date: 25-01-2016
Publisher: American Astronomical Society
Date: 10-2021
Publisher: Springer Science and Business Media LLC
Date: 26-08-2019
Publisher: American Astronomical Society
Date: 10-2021
DOI: 10.3847/PSJ/AC1C6B
Publisher: American Astronomical Society
Date: 29-06-2017
Publisher: American Astronomical Society
Date: 03-05-2017
Publisher: American Astronomical Society
Date: 25-03-2021
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 1 km s −1 and are dominated by the main classical belt.
Publisher: American Astronomical Society
Date: 11-05-2018
Publisher: American Astronomical Society
Date: 13-07-2017
Publisher: American Astronomical Society
Date: 30-11-2022
Abstract: We investigate different conditions, including the orbital and size–frequency distribution (SFD) of the early Kuiper Belt, that can trigger catastrophic planetesimal destruction. The goal of this study is to test if there is evidence for collisional grinding in the Kuiper Belt that has occurred since its formation. This analysis has important implications for whether the present-day SFD of the cold classical trans-Neptunian objects (TNOs) is a result of collisional equilibrium or if it reflects the primordial stage of planetesimal accretion. As an input to our modeling, we use the most up-to-date debiased OSSOS++ ensemble s le of the TNO population and orbital model based on the present-day architecture of the Kuiper Belt. We calculate the specific impact energies between impactor–target pairs from different TNO groups and compare our computed energies to catastrophic disruption results from smoothed particle hydrodynamics simulations. We explore different scenarios by considering different total primordial Kuiper Belt masses and power slopes of the SFD and allowing collisions to take place over different timescales. The collisional evolution of the Kuiper Belt is a strong function of the unknown initial mass in the trans-Neptunian region, where collisional grinding of planetesimals requires a total primordial Kuiper Belt mass of M 5 M ⊕ , collision speeds as high as 3 km s −1 , and collisions over at least 0.5 Gyr. We conclude that presently, most of the collisions in the trans-Neptunian region are in the cratering rather than disruption regime. Given the low collision rates among the cold classical Kuiper Belt objects, their SFD most likely represents the primordial planetesimal accretion.
Publisher: American Astronomical Society
Date: 19-09-2019
Publisher: American Astronomical Society
Date: 18-04-2018
Publisher: American Astronomical Society
Date: 19-05-2017
Publisher: American Astronomical Society
Date: 20-05-2020
DOI: 10.3847/PSJ/AB8CC0
Abstract: The surface characterization of Trans-Neptunian binaries (TNBs) is key to understanding the properties of the disk of planetesimals from which these objects formed. In the optical wavelengths, it has been demonstrated that most equal-sized component systems share similar colors, suggesting they have a similar composition. The color homogeneity of binary pairs contrasts with the overall ersity of colors in the Kuiper Belt, which was interpreted as evidence that Trans-Neptunian objects (TNOs) formed from a locally homogeneous and globally heterogeneous protoplanetary disk. In this paradigm, binary pairs must have formed early, before the dynamically hot TNOs were scattered out from their formation location. The latter inferences, however, relied on the assumption that the matching colors of the binary components imply matching composition. Here, we test this assumption by examining the component-resolved photometry of three TNBs found in the Outer Solar System Origins Survey: 505447 (2013 SQ99), 511551 (2014 UD225), and 506121 (2016 BP81), across the visible and J -band near-infrared wavelength range. We report similar colors within 2 σ for the binary pairs, which is suggestive of similar reflectance spectra and hence surface composition. This advocates for gravitational collapse of pebble clouds as a possible TNO formation route. However, we stress that several similarly small TNOs, including at least one binary, have been shown to exhibit substantial spectral variability in the near-infrared, implying color equality of binary pairs is likely to be violated in some cases.
Publisher: American Astronomical Society
Date: 31-08-2016
Publisher: Elsevier BV
Date: 03-2021
Publisher: American Astronomical Society
Date: 11-07-2019
Publisher: American Astronomical Society
Date: 2022
DOI: 10.3847/PSJ/AC42C9
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.
Publisher: American Astronomical Society
Date: 05-12-2016
Location: United States of America
No related grants have been discovered for Mike Alexandersen.