arXiv subjects

M. T. Bannister

Publications and source records attributed to M. T. Bannister.

11 recordsLinked to original sources

arXiv2022

OSSOS XXV: Large Populations and Scattering-Sticking in the Distant Transneptunian Resonances

There have been 77 TNOs discovered to be librating in the distant transneptunian 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.

astro-ph.EP↗

arXiv2020

The carbon monoxide-rich interstellar comet 2I/Borisov

Interstellar comets offer direct samples of volatiles from distant protoplanetary disks. 2I/Borisov is the first notably active interstellar comet discovered in our solar system[1]. Comets are condensed samples of the gas, ice, and dust that were in a star's protoplanetary disk during the formation of its planets and inform our understanding on how chemical compositions and abundances vary with distance from the central star. Their orbital migration moves volatiles[2], organic material, and prebiotic chemicals in their host system[3]. In our solar system, hundreds of comets have been observed remotely, and a few have been studied up close by space missions[4]. However, knowledge of extrasolar comets has been limited to what could be gleaned from distant, unresolved observations of cometary regions around other stars, with only one detection of carbon monoxide[5]. Here we report that the coma of 2I/Borisov contains significantly more CO than H2O gas, with abundances of at least 173%, more than three times higher than previously measured for any comet in the inner (<2.5 au) solar system[4]. Our ultraviolet observations of 2I/Borisov provide the first glimpse into the ice content and chemical composition of the protoplanetary disk of another star that is substantially different from our own.

astro-ph.EP↗

arXiv2019

OSSOS: XIII. Fossilized Resonant Dropouts Tentatively Confirm Neptune's Migration was Grainy and Slow

The migration of Neptune's resonances through the proto-Kuiper belt has been imprinted in the distribution of small bodies in the outer Solar System. Here we analyze five published Neptune migration models in detail, focusing on the high pericenter distance (high-q) trans-Neptunian Objects (TNOs) near Neptune's 5:2 and 3:1 mean-motion resonances, because they have large resonant populations, are outside the main classical belt, and are relatively isolated from other strong resonances. We compare the observationally biased output from these dynamical models with the detected TNOs from the Outer Solar System Origins Survey, via its Survey Simulator. All of the four new OSSOS detections of high-q non-resonant TNOs are on the Sunward side of the 5:2 and 3:1 resonances. We show that even after accounting for observation biases, this asymmetric distribution cannot be drawn from a uniform distribution of TNOs at 2sigma confidence. As shown by previous work, our analysis here tentatively confirms that the dynamical model that uses grainy slow Neptune migration provides the best match to the real high-q TNO orbital data. However, due to extreme observational biases, we have very few high-q TNO discoveries with which to statistically constrain the models. Thus, this analysis provides a framework for future comparison between the output from detailed, dynamically classified Neptune migration simulations and the TNO discoveries from future well-characterized surveys. We show that a deeper survey (to a limiting r-magnitude of 26.0) with a similar survey area to OSSOS could statistically distinguish between these five Neptune migration models.

astro-ph.EP↗

arXiv2018

OSSOS: XV. No active Centaurs in the Outer Solar System Origins Survey

Context. Centaurs are icy objects in transition between the transneptunian 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 look at 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 (PSF) and Trailed point-Spread Functions (TSF) from the OSSOS images of each Centaur. When available, Col-OSSOS images were used to search for comae too. Results. No cometary activity is detected in the OSSOS sample. 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.

astro-ph.EP↗

arXiv2018

Solar system science with the Wide-Field InfraRed Survey Telescope (WFIRST)

We present a community-led assessment of the solar system investigations achievable with NASA's next-generation space telescope, the Wide Field InfraRed Survey Telescope (WFIRST). WFIRST will provide imaging, spectroscopic, and coronagraphic capabilities from 0.43-2.0 $μ$m and will be a potential contemporary and eventual successor to JWST. Surveys of irregular satellites and minor bodies are where WFIRST will excel with its 0.28 deg$^2$ field of view Wide Field Instrument (WFI). Potential ground-breaking discoveries from WFIRST could include detection of the first minor bodies orbiting in the Inner Oort Cloud, identification of additional Earth Trojan asteroids, and the discovery and characterization of asteroid binary systems similar to Ida/Dactyl. Additional investigations into asteroids, giant planet satellites, Trojan asteroids, Centaurs, Kuiper Belt Objects, and comets are presented. Previous use of astrophysics assets for solar system science and synergies between WFIRST, LSST, JWST, and the proposed NEOCam mission are discussed. We also present the case for implementation of moving target tracking, a feature that will benefit from the heritage of JWST and enable a broader range of solar system observations.

astro-ph.EP↗

arXiv2018

OSSOS: X. How to use a Survey Simulator: Statistical Testing of Dynamical Models Against the Real Kuiper Belt

All surveys include observational biases, which makes it impossible to directly compare properties of discovered trans-Neptunian Objects (TNOs) with dynamical models. However, by carefully keeping track of survey pointings on the sky, detection limits, tracking fractions, and rate cuts, the biases from a survey can be modelled in Survey Simulator software. A Survey Simulator takes an intrinsic orbital model (from, for example, the output of a dynamical Kuiper belt emplacement simulation) and applies the survey biases, so that the biased simulated objects can be directly compared with real discoveries. This methodology has been used with great success in the Outer Solar System Origins Survey (OSSOS) and its predecessor surveys. In this chapter, we give four examples of ways to use the OSSOS Survey Simulator to gain knowledge about the true structure of the Kuiper Belt. We demonstrate how to statistically compare different dynamical model outputs with real TNO discoveries, how to quantify detection biases within a TNO population, how to measure intrinsic population sizes, and how to use upper limits from non-detections. We hope this will provide a framework for dynamical modellers to statistically test the validity of their models.

astro-ph.EP↗

arXiv2018

OSSOS. VIII. The Transition Between Two Size Distribution Slopes in the Scattering Disk

The scattering trans-Neptunian Objects (TNOs) can be measured to smaller sizes than any other distant small-body population. We use the largest sample yet obtained, 68 discoveries, primarily by the Outer Solar System Origins Survey (OSSOS), to constrain the slope of its luminosity distribution, with sensitivity to much fainter absolute $H$ magnitudes than previous work. Using the analysis technique in Shankman et al. (2016), we confirm that a single slope for the $H$-distribution is not an accurate representation of the scattering TNOs and Centaurs, and that a break in the distribution is required, in support of previous conclusions. A bright-end slope of $α_b=0.9$ transitioning to a faint-end slope $α_f$ of 0.4-0.5 with a differential number contrast $c$ from 1 (a knee) to 10 (a divot) provides an acceptable match to our data. We find that break magnitudes $H_b$ of 7.7 and 8.3, values both previously suggested for dynamically hot Kuiper belt populations, are equally non-rejectable for a range of $α_f$ and $c$ in our statistical analysis. Our preferred divot $H$-distribution transitions to $α_f=0.5$ with a divot of contrast $c=3$ at $H_b=8.3$, while our preferred knee $H$-distribution transitions to $α_f=0.4$ at $H_b=7.7$. The intrinsic population of scattering TNOs required to match the OSSOS detections is $3\times10^6$ for $H_r<12$, and $9\times10^4$ for $H_r<8.66$ ($D\gtrsim100$~km), with Centaurs having an intrinsic population two orders of magnitude smaller.

astro-ph.EP↗

arXiv2016

Observational Signatures of a Massive Distant Planet on the Scattering Disk

The orbital element distribution of trans-Neptunian objects (TNOs) with large pericenters has been suggested to be influenced by the presence of an undetected, large planet at >200 AU from the Sun. To find additional observables caused by this scenario, we here present the first detailed emplacement simulation in the presence of a massive ninth planet on the distant Kuiper Belt. We perform 4 Gyr N-body simulations with the currently known Solar System planetary architecture, plus a 10 Earth mass planet with similar orbital parameters to those suggested by Trujillo & Sheppard (2014) or Batygin & Brown (2016), and 10^5 test particles in an initial planetesimal disk. We find that including a distant superearth-mass planet produces a substantially different orbital distribution for the scattering and detached TNOs, raising the pericenters and inclinations of moderate semimajor axis (50<a<500 AU) objects. We test whether this signature is detectable via a simulator with the observational characteristics of four precisely characterized TNO surveys. We find that the qualitatively very distinct Solar System models that include a ninth planet are essentially observationally indistinguishable from an outer Solar System produced solely by the four giant planets. We also find that the mass of the Kuiper Belt's current scattering and detached populations is required to be 3-10 times larger in the presence of an additional planet. We do not find any evidence for clustering of orbital angles in our simulated TNO population. Wide-field, deep surveys targeting inclined high-pericenter objects will be required to distinguish between these different scenarios.

astro-ph.EP↗

arXiv2016

Consequences of a Distant Massive Planet on the Large Semi-major Axis Trans-Neptunian Objects

We explore the distant giant planet hypothesis by integrating the large semi-major axis, large pericenter Trans-Neptunian Objects (TNOs) in the presence of the giant planets and an external perturber whose orbit is consistent with the proposed distant, eccentric, and inclined giant planet, so called planet 9. We find that TNOs with semi-major axes greater than 250 au experience some longitude of perihelion shepherding, but that a generic outcome of such evolutions is that the TNOs evolve to larger pericenter orbits, and commonly get raised to retrograde inclinations. This pericenter and inclination evolution requires a massive disk of TNOs (tens of M$_\Earth$) in order to explain the detection of the known sample today. Some of the highly inclined orbits produced by the examined perturbers will be inside of the orbital parameter space probed by prior surveys, implying a missing signature of the 9th planet scenario. The distant giant planet scenarios explored in this work do not reproduce the observed signal of simultaneous clustering in argument of pericenter, longitude of the ascending node, and longitude of perihelion in the region of the known TNOs.

astro-ph.EP↗

arXiv2015

OSSOS II: A Sharp Transition in the Absolute Magnitude Distribution of the Kuiper Belt's Scattering Population

We measure the absolute magnitude, $H$, distribution, $dN(H) \propto 10^{αH}$ of the scattering Trans-Neptunian Objects (TNOs) as a proxy for their size-frequency distribution. We show that the H-distribution of the scattering TNOs is not consistent with a single-slope distribution, but must transition around $H_g \sim 9$ to either a knee with a shallow slope or to a divot, which is a differential drop followed by second exponential distribution. Our analysis is based on a sample of 22 scattering TNOs drawn from three different TNO surveys, the Canada-France Ecliptic Plane Survey (CFEPS, Petit et al. 2011), Alexandersen et al. (2014), and the Outer Solar System Origins Survey (OSSOS, Bannister et al. 2016), all of which provide well characterized detection thresholds, combined with a cosmogonic model for the formation of the scattering TNO population. Our measured absolute magnitude distribution result is independent of the choice of cosmogonic model. Based on our analysis, we estimate that number of scattering TNOs is (2.4-8.3)$\times 10^5$ for $H_r < 12$. A divot $H$-distribution is seen in a variety of formation scenarios and may explain several puzzles in Kuiper Belt science. We find that a divot $H$-distribution simultaneously explains the observed scattering TNO, Neptune Trojan, Plutino, and Centaur $H$-distributions while simultaneously predicting a large enough scattering TNO population to act as the sole supply of the Jupiter-Family Comets.

astro-ph.EP↗

arXiv2012

2008 LC18: a potentially unstable Neptune Trojan

The recent discovery of the first Neptune Trojan at the planet's trailing (L5) Lagrange point, 2008 LC18, offers an opportunity to confirm the formation mechanism of a member of this important tracer population for the Solar system's dynamical history. We tested the stability of 2008 LC18's orbit through a detailed dynamical study, using test particles spread across the orbital uncertainties in a, e, i and Ω. This showed that the wide uncertainties of the published orbit span regions of both extreme dynamical instability, with lifetimes < 100 Myr, and with significant stability (> 1 Gyr lifetimes). The stability of 2008 LC18's clones is greatly dependent on their semi-major axis and only weakly correlated with their eccentricity. Test particles on orbits with an initial semi-major axis less than 29.91 AU have dynamical half-lives shorter than 100 Myr; in contrast, particles with an initial semi-major axis greater than 29.91 AU exhibit such strong dynamical stability that almost all are retained over the 1 Gyr of our simulations. More observations of this object are necessary to improve the orbit. If 2008 LC18 is in the unstable region, then our simulations imply that it is either a temporary Trojan capture, or a representative of a slowly decaying Trojan population (like its sibling the L4 Neptunian Trojan 2001 QR322), and that it may not be primordial. Alternatively, if the orbit falls into the larger, stable region, then 2008 LC18 is a primordial member of the highly stable and highly inclined component of the Neptune Trojan population, joining 2005 TN53 and 2007 VL305. We attempted to recover 2008 LC18 using the 2.3m telescope at Siding Spring Observatory to provide this astrometry, but were unsuccessful due to the high stellar density of its current sky location near the galactic centre. The recovery of this object will require a telescope in the 8m class.

astro-ph.EP↗