arXiv subjects

Michele T. Bannister

Publications and source records attributed to Michele T. Bannister.

At least 37 records · Page 2Linked to original sources

arXiv2024

Predicting Interstellar Object Chemodynamics with Gaia

The interstellar object population of the Milky Way is a product of its stars. However, what is in fact a complex structure in the Solar neighbourhood has traditionally in ISO studies been described as smoothly distributed. Using a debiased stellar population derived from the Gaia DR3 stellar sample, we predict that the velocity distribution of ISOs is far more textured than a smooth Gaussian. The moving groups caused by Galactic resonances dominate the distribution. 1I/`Oumuamua and 2I/Borisov have entirely normal places within these distributions; 1I is within the non-coeval moving group that includes the Matariki (Pleiades) cluster, and 2I within the Coma Berenices moving group. We show that for the composition of planetesimals formed beyond the ice line, these velocity structures also have a chemodynamic component. This variation will be visible on the sky. We predict that this richly textured distribution will be differentiable from smooth Gaussians in samples that are within the expected discovery capacity of the Vera C. Rubin Observatory. Solar neighbourhood ISOs will be of all ages and come from a dynamic mix of many different populations of stars, reflecting their origins from all around the Galactic disk.

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arXiv2024

Fast Radio Bursts and Interstellar Objects

Fast radio bursts (FRBs) are transient radio events with millisecond-scale durations, and debated origins. Collisions between planetesimals and neutron stars have been proposed as a mechanism to produce FRBs; the planetesimal strength, size and density determine the time duration and energy of the resulting event. One source of planetesimals is the population of interstellar objects (ISOs), free-floating objects expected to be extremely abundant in galaxies across the Universe as products of planetary formation. We explore using the ISO population as a reservoir of planetesimals for FRB production, finding that the expected ISO-neutron star collision rate is comparable with the observed FRB event rate. Using a model linking the properties of planetesimals and the FRBs they produce, we further show that observed FRB durations are consistent with the sizes of known ISOs, and the FRB energy distribution is consistent with the observed size distributions of Solar System planetesimal populations. Finally, we argue that the rate of ISO-neutron star collisions must increase with cosmic time, matching the observed evolution of the FRB rate. Thus, ISO-neutron star collisions are a feasible mechanism for producing FRBs.

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arXiv2024

The Volatile Composition and Activity Evolution of Main-Belt Comet 358P/PANSTARRS

We report the detection of water vapor associated with main-belt comet 358P/PANSTARRS on UT 2024 January 8-9 using the NIRSPEC instrument aboard JWST. We derive a water production rate of Q(H2O)=(5.0+/-0.2)x10^25 molecules/s, marking only the second direct detection of sublimation products of any kind from a main-belt comet, after 238P/Read. Similar to 238P, we find a remarkable absence of hypervolatile species, finding Q(CO2)<7.6x10^22 molecules/s, corresponding to Q(CO2)/Q(H2O)<0.2%. Upper limits on CH3OH and CO emission are also estimated. Photometry from ground-based observations show that the dust coma brightened and faded slowly over ~250 days in 2023-2024, consistent with photometric behavior observed in 2012-2013, but also indicate a ~2.5x decline in the dust production rate between these two periods. Dynamical dust modeling shows that the coma's morphology as imaged by JWST's NIRCAM instrument on 2023 November 22 can be reproduced by asymmetric dust emission from a nucleus with a mid-range obliquity (~80 deg) with a steady-state mass loss rate of ~0.8 kg/s. Finally, we find similar Afrho-to-gas ratios of log10(Afrho/Q(H2O))=-24.8+/-0.2 for 358P and log10(Afrho/QH2O)=-24.4+/-0.2 for 238P, suggesting that Afrho could serve as an effective proxy for estimating water production rates in other active main-belt comets. The confirmation of water vapor outgassing in both main-belt comets observed by JWST to date reinforces the use of recurrent activity near perihelion as an indicator of sublimation-driven activity in active asteroids.

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arXiv2024

Rubin ToO 2024: Envisioning the Vera C. Rubin Observatory LSST Target of Opportunity program

The Legacy Survey of Space and Time (LSST) at Vera C. Rubin Observatory is planned to begin in the Fall of 2025. The LSST survey cadence has been designed via a community-driven process regulated by the Survey Cadence Optimization Committee (SCOC), which recommended up to 3% of the observing time to carry out Target of Opportunity (ToO) observations. Experts from the scientific community, Rubin Observatory personnel, and members of the SCOC were brought together to deliver a recommendation for the implementation of the ToO program during a workshop held in March 2024. Four main science cases were identified: gravitational wave multi-messenger astronomy, high energy neutrinos, Galactic supernovae, and small potentially hazardous asteroids possible impactors. Additional science cases were identified and briefly addressed in the documents, including lensed or poorly localized gamma-ray bursts and twilight discoveries. Trigger prioritization, automated response, and detailed strategies were discussed for each science case. This document represents the outcome of the Rubin ToO 2024 workshop, with additional contributions from members of the Rubin Science Collaborations. The implementation of the selection criteria and strategies presented in this document has been endorsed in the SCOC Phase 3 Recommendations document (PSTN-056). Although the ToO program is still to be finalized, this document serves as a baseline plan for ToO observations with the Rubin Observatory.

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arXiv2023

The Galactic Interstellar Object Population: A Framework for Prediction and Inference

The Milky Way is thought to host a huge population of interstellar objects (ISOs), numbering approximately $10^{15}\mathrm{pc}^{-3}$ around the Sun, which are formed and shaped by a diverse set of processes ranging from planet formation to galactic dynamics. We define a novel framework: firstly to predict the properties of this Galactic ISO population by combining models of processes across planetary and galactic scales, and secondly to make inferences about the processes modelled, by comparing the predicted population to what is observed. We predict the spatial and compositional distribution of the Galaxy's population of ISOs by modelling the Galactic stellar population with data from the APOGEE survey and combining this with a protoplanetary disk chemistry model. Selecting ISO water mass fraction as an example observable quantity, we evaluate its distribution both at the position of the Sun and averaged over the Galactic disk; our prediction for the Solar neighbourhood is compatible with the inferred water mass fraction of 2I/Borisov. We show that the well-studied Galactic stellar metallicity gradient has a corresponding ISO compositional gradient. We also demonstrate the inference part of the framework by using the current observed ISO composition distribution to constrain the parent star metallicity dependence of the ISO production rate. This constraint, and other inferences made with this framework, will improve dramatically as the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) progresses and more ISOs are observed. Finally, we explore generalisations of this framework to other Galactic populations, such as that of exoplanets.

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arXiv2023

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 (Col-OSSOS) acquired multi-band 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

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arXiv2023

Ejecta Evolution Following a Planned Impact into an Asteroid: The First Five Weeks

The impact of the DART spacecraft into Dimorphos, moon of the asteroid Didymos, changed Dimorphos' orbit substantially, largely from the ejection of material. We present results from twelve Earth-based facilities involved in a world-wide campaign to monitor the brightness and morphology of the ejecta in the first 35 days after impact. After an initial brightening of ~1.4 magnitudes, we find consistent dimming rates of 0.11-0.12 magnitudes/day in the first week, and 0.08-0.09 magnitudes/day over the entire study period. The system returned to its pre-impact brightness 24.3-25.3 days after impact through the primary ejecta tail remained. The dimming paused briefly eight days after impact, near in time to the appearance of the second tail. This was likely due to a secondary release of material after re-impact of a boulder released in the initial impact, through movement of the primary ejecta through the aperture likely played a role.

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arXiv2023

The hot main Kuiper belt size distribution from OSSOS

Using the absolute detection calibration and abundant detections of the OSSOS (Outer Solar System Origin Survey) project, we provide population measurements for the main Kuiper Belt. For absolute magnitude $H_r<8.3$, there are 30,000 non-resonant main-belt objects, with twice as many hot-component objects than cold, and with total mass of 0.014 $M_\Earth$, only 1/7 of which is in the cold belt (assuming a cold-object albedo about half that of hot component objects). We show that transneptunian 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, % << BG added clause 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.

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arXiv2023

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 semi-major axis, centred at $\sim$24.6 au and $\sim$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 (OSSOS) survey simulator to calculate the detection efficiency for these objects in an ensemble of fully characterised surveys, we determine that a population of 72 stable Centaurs with absolute magnitude $H_{r}\leq10$ ($95\%$ confidence upper limit) could remain undetected. The upcoming Legacy Survey of Space and Time (LSST) 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.

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arXiv2023

Tuning the Legacy Survey of Space and Time (LSST) Observing Strategy for Solar System Science

The Vera C. Rubin Observatory is expected to start the Legacy Survey of Space and Time (LSST) in early to mid-2025. This multi-band wide-field synoptic survey will transform our view of the solar system, with the discovery and monitoring of over 5 million small bodies.The final survey strategy chosen for LSST has direct implications on the discoverability and characterization of solar system minor planets and passing interstellar objects. Creating an inventory of the solar system is one of the four main LSST science drivers. The LSST observing cadence is a complex optimization problem that must balance the priorities and needs of all the key LSST science areas. To design the best LSST survey strategy, a series of operation simulations using the Rubin Observatory scheduler have been generated to explore the various options for tuning observing parameters and prioritizations. We explore the impact of the various simulated LSST observing strategies on studying the solar system's small body reservoirs. We examine what are the best observing scenarios and review what are the important considerations for maximizing LSST solar system science. In general, most of the LSST cadence simulations produce +/-5% or less variations in our chosen key metrics, but a subset of the simulations significantly hinder science returns with much larger losses in the discovery and light curve metrics.

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arXiv2023

Ejecta from the DART-produced active asteroid Dimorphos

Some active asteroids have been proposed to be the result of impact events. Because active asteroids are generally discovered serendipitously only after their tail formation, the process of the impact ejecta evolving into a tail has never been directly observed. NASA's Double Asteroid Redirection Test (DART) mission, apart from having successfully changed the orbital period of Dimorphos, demonstrated the activation process of an asteroid from an impact under precisely known impact conditions. Here we report the observations of the DART impact ejecta with the Hubble Space Telescope (HST) from impact time T+15 minutes to T+18.5 days at spatial resolutions of ~2.1 km per pixel. Our observations reveal a complex evolution of ejecta, which is first dominated by the gravitational interaction between the Didymos binary system and the ejected dust and later by solar radiation pressure. The lowest-speed ejecta dispersed via a sustained tail that displayed a consistent morphology with previously observed asteroid tails thought to be produced by impact. The ejecta evolution following DART's controlled impact experiment thus provides a framework for understanding the fundamental mechanisms acting on asteroids disrupted by natural impact.

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arXiv2022

The LCO Outbursting Objects Key Project: Overview and Year 1 Status

The LCO Outbursting Objects Key (LOOK) Project uses the telescopes of the Las Cumbres Observatory (LCO) Network to: (1) to systematically monitor a sample of Dynamically New Comets over the whole sky, and (2) use alerts from existing sky surveys to rapidly respond to and characterize detected outburst activity in all small bodies. The data gathered on outbursts helps to characterize each outburst's evolution with time, assess the frequency and magnitude distribution of outbursts in general, and contributes to the understanding of outburst processes and volatile distribution in the Solar System. The LOOK Project exploits the synergy between current and future wide-field surveys such as ZTF, PanSTARRS, and LSST as well as rapid-response telescope networks such as LCO, and serves as an excellent testbed for what will be needed the much larger number of objects coming from Rubin Observatory. We will describe the LOOK Project goals, the planning and target selection (including the use of NEOexchange as a Target and Observation Manager or "TOM"), and results from the first phase of observations, including the detection of activity and outbursts on the giant comet C/2014 UN271 (Bernardinelli-Bernstein) and the discovery and follow-up of outbursts on comets. Within these outburst discoveries, we present a high cadence of 7P/Pons-Winnecke with days, a large outburst on 57P/duToit-Neujmin-Delporte, and evidence that comet P/2020 X1 (ATLAS) was in outburst when discovered.

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arXiv2022

Col-OSSOS: The Two Types of Kuiper Belt Surfaces

The Colours of the Outer Solar System Origins Survey (Col-OSSOS) has gathered high quality, near-simultaneous (g-r) and (r-J) colours of 92 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 colours of most icy bodies broadly follow the reddening curve, we present a new projection of the optical-NIR colours, which rectifies the main non-linear features in the optical-NIR along the ordinates. We find evidence for a bifurcation in the projected colours which presents itself as a diagonal empty region in the optical-NIR. A reanalysis of past colour surveys reveals the same bifurcation. We interpret this as evidence for two separate surface classes: the BrightIR class spans the full range of optical colours and broadly follows the reddening curve, while the FaintIR objects are limited in optical colour, 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 colour. Spectra are modelled as linear optical and NIR spectra with different slopes, that intersect at some transition wavelength. The underlying spectral properties of the two classes fully reproduce the observed structures in the UV-optical-NIR colour space ($0.4\lesssimλ\lesssim1.4 \mbox{ $μ$m}$), including the bifurcation observed in the Col-OSSOS and H/WTSOSS datasets, the tendency for cold classical KBOs to have lower (r-z) colours than excited objects, and the well known bimodal optical colour distribution.

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arXiv2022

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. In a companion paper by Fraser et al., we demonstrate 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 is governed by a mixture of two material end members. Here, we investigate the orbital distribution of the two color classes identified by Fraser et al. and find that the orbital inclinations of the brightIR class objects are correlated with their optical colors. Using the output of numerical simulations investigating the orbital evolution of TNOs during their scattering phase with Neptune, we show that this correlation 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.

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arXiv2021

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

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 $28^{+2}_{-3}$ 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.

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arXiv2021

Predicting the water content of interstellar objects from galactic star formation histories

Planetesimals inevitably bear the signatures of their natal environment, preserving in their composition a record of the metallicity of their system's original gas and dust, albeit one altered by the formation process. When planetesimals are dispersed from their system of origin, this record is carried with them. As each star is likely to contribute at least $10^{12}$ interstellar objects, the Galaxy's drifting population of interstellar objects (ISOs) provides an overview of the properties of its stellar population through time. Using the EAGLE cosmological simulation and models of protoplanetary formation, our modelling predicts an ISO population with a bimodal distribution in their water mass fraction. Objects formed in low-metallicity, typically older, systems have a higher water fraction than their counterparts formed in high-metallicity protoplanetary disks, and these water-rich objects comprise the majority of the population. Both detected ISOs seem to belong to the lower water fraction population; these results suggest they come from recently formed systems. We show that the population of ISOs in galaxies with different star formation histories will have different proportions of objects with high and low water fractions. This work suggests that it is possible that the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time will detect a large enough population of ISOs to place useful constraints on models of protoplanetary disks, as well as galactic structure and evolution.

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arXiv2021

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

We present the discovery of 2013 VZ70, the first known horseshoe coorbital companion of Saturn. Observed by the Outer Solar System Origins Survey (OSSOS) for 4.5 years, 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 transneptunian source.

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arXiv2021

OSSOS finds an Exponential Cutoff in the Size Distribution of the Cold Classical Kuiper belt

The cold main classical Kuiper Belt consists of those non-resonant small solar system bodies with low orbital inclinations and orbital semi-major axes between 42.4 and 47.7 au. These objects likely formed \textit{in situ} and the population has experienced minimal collisional modification since formation. Using the Outer Solar System Origins Survey (OSSOS) 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 $H_r\simeq5$ to 12 (roughly diameters of 400 km to 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 pair-wise 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 ($D \gtrsim 400$ km) exist in the cold population. We note that the asymptotic slope of the $H_r$ distribution is consistent with $α\sim 0.4$ and this asymptotic slope is also found in streaming instability modelling of planetesimal formation and is thus not necessarily associated with achieving collisional equilibrium. Studies of the transneptunian region are providing the parameters that will enable future streaming-instability studies to determine the initial conditions of planetesimal formation in the $\approx$45 au region of the Sun's protoplanetary disk.

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