arXiv subjects

Mark A. Hutchison

Publications and source records attributed to Mark A. Hutchison.

10 recordsLinked to original sources

arXiv2026

Dust Processing in Protoplanetary Discs From Infall to Dispersal: the Origin of Solar System Isotopic Heterogeneities

The nucleosynthetic heterogeneity between different asteroids and planets is well established. These isotopic variations manifest themselves at the part per millions level or larger, in isotopes that were synthesised in various stellar environments. To escape homogenisation, some of these isotopic signatures must have been preserved in dust, which ended up being heterogeneously distributed in the solar protoplanetary disc. The origin of the nucleosynthetic heterogeneity is still poorly constrained, potentially reflecting inherited isotope variations from the Sun's parental molecular cloud and/or processing and redistribution during the subsequent protoplanetary disc phase with thermal processing and size sorting as major processes. This chapter aims to provide a broad review of the dynamical, collisional, and thermal processes in protoplanetary discs -- from initial infall to gas dispersal -- that may have influenced the distribution and survival of the anomalous carrier phases, which finally accreted into asteroids and planets. While several of these mechanisms have been considered in past studies, they are often examined in isolation, which impedes the assessment of how their effects may be altered or amplified by additional disc processes. Size sorting in particular has received little attention, and here we highlight that this process likely occurred in the disc and can induce nucleosynthetic heterogeneity. By placing previous studies within the context of a comprehensive overview, we aim to clarify the broader physical framework in which anomalous carrier transport occurs and identify previously underexplored mechanisms that may have contributed to the final isotopic structure of the Solar System we see today.

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arXiv2025

Modelling dust coagulation, dynamical drag and turbulent mixing during star and disc formation

Planet formation in the discs around young stars involves the coagulation of sub-micron sized dust grains into much larger grains that may be mixed by turbulence and migrate through the disc. In this paper, we describe how we have combined a method for modelling the coagulation of a population of dust grains with the MULTIGRAIN algorithm for modelling the dynamical evolution of a population of dust grains that are subject to strong gas drag. We solve the dynamical evolution of the dust grains due to gas drag using a recently-developed implicit integration method, and we introduce a new implicit method to model the diffusion of the dust due to unresolved hydrodynamic turbulence. The resulting smoothed particle hydrodynamics (SPH) code allows us, for the first time, to model the growth, mixing and migration of dust grain populations during the early stages of star formation and the formation, growth and evolution of a young protoplanetary disc using three-dimensional hydrodynamical simulations. In doing so, we find that including turbulent dust diffusion within the disc provides a substantial enhancement of the rate of dust grain growth due to the fact that the turbulent diffusion provides a source of small and intermediate dust grains to the regions in which the largest dust grains are growing.

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arXiv2024

Contour Analysis Tool: an interactive tool for background and morphology analysis

We introduce the Contour Analysis Tool (CAT), a Python toolkit aimed at identifying and analyzing structural elements in density maps. CAT employs various contouring techniques, including the lowest-closed contour (LCC), linear and logarithmic Otsu thresholding, and average gradient thresholding. These contours can aid in foreground and background segmentation, providing natural limits for both, as well as edge detection and structure identification. Additionally, CAT provides image processing methods such as smoothing, background removal, and image masking. The toolkit features an interactive suite of controls designed for Jupyter environments, enabling users to promptly visualize the effects of different methods and parameters. We describe, test, and demonstrate the performance of CAT, highlighting its potential use cases. CAT is publicly available on GitHub, promoting accessibility and collaboration.

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arXiv2022

Presolar grain dynamics: creating nucleosynthetic variations through a combination of drag and viscous evolution

Meteoritic studies of solar system objects show evidence of nucleosynthetic heterogeneities that are inherited from small presolar grains (< 10 $μ$m) formed in stellar environments external to our own. The initial distribution and subsequent evolution of these grains are currently unconstrained. Using 3D, gas-dust simulations, we find that isotopic variations on the order of those observed in the solar system can be generated and maintained by drag and viscosity. Small grains are dragged radially outwards without size/density sorting by viscous expansion and backreaction, enriching the outer disc with presolar grains. Meanwhile large aggregates composed primarily of silicates drift radially inwards due to drag, further enriching the relative portion of presolar grains in the outer disc and diluting the inner disc. The late accumulation of enriched aggregates outside Jupiter could explain some of the isotopic variations observed in solar system bodies, such as the enrichment of supernovae derived material in carbonaceous chondrites. We also see evidence for isotopic variations in the inner disc that may hold implications for enstatite and ordinary chondrites that formed closer to the Sun. Initial heterogeneities in the presolar grain distribution that are not continuously reinforced are dispersed by diffusion, radial surface flows, and/or planetary interactions over the entire lifetime of the disc. For younger, more massive discs we expect turbulent diffusion to be even more homogenising, suggesting that dust evolution played a more central role in forming the isotopic anomalies in the solar system than originally thought.

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arXiv2020

Dust delivery and entrainment in photoevaporative winds

We model the gas and dust dynamics in a turbulent protoplanetary disc undergoing extreme-UV photoevaporation in order to better characterise the dust properties in thermal winds (e.g. size distribution, flux rate, trajectories). Our semi-analytic approach allows us to rapidly calculate these dust properties without resorting to expensive hydrodynamic simulations. We find that photoevaporation creates a vertical gas flow within the disc that assists turbulence in supplying dust to the ionisation front. We examine both the delivery of dust to the ionisation front and its subsequent entrainment in the overlying wind. We derive a simple analytic criterion for the maximum grain size that can be entrained and show that this is in good agreement with the results of previous simulations where photoevaporation is driven by a range of radiation types. We show that, in contrast to the case for magnetically driven winds, we do not expect large scale dust transport within the disc to be effected by photoevaporation. We also show that the maximum size of grains that can be entrained in the wind ($s_{\rm max}$) is around an order of magnitude larger than the maximum size of grains that can be delivered to the front by advection alone ($s_{\rm crit} \lesssim 1$ $μ{\rm m}$ for Herbig Ae/Be stars and $\lesssim 0.01$ $μ{\rm m}$ for T Tauri stars). We further investigate how larger grains, up to a limiting size $s_{\rm limit}$, can be delivered to the front by turbulent diffusion alone. In all cases, we find $s_{\rm max} \gtrsim s_{\rm limit}$ so that we expect that any dust that is delivered to the front can be entrained in the wind and that most entrained dust follows trajectories close to that of the gas.

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arXiv2018

MULTIGRAIN: A smoothed particle hydrodynamics algorithm for multiple small dust grains and gas

We present a new algorithm, MULTIGRAIN, for modelling the dynamics of an entire population of small dust grains immersed in gas, typical of conditions that are found in molecular clouds and protoplanetary discs. The MULTIGRAIN method is more accurate than single-phase simulations because the gas experiences a backreaction from each dust phase and communicates this change to the other phases, thereby indirectly coupling the dust phases together. The MULTIGRAIN method is fast, explicit and low storage, requiring only an array of dust fractions and their derivatives defined for each resolution element.

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arXiv2016

Grand challenges in protoplanetary disc modelling

The Protoplanetary Discussions conference --- held in Edinburgh, UK, from 7th --11th March 2016 --- included several open sessions led by participants. This paper reports on the discussions collectively concerned with the multiphysics modelling of protoplanetary discs, including the self-consistent calculation of gas and dust dynamics, radiative transfer and chemistry. After a short introduction to each of these disciplines in isolation, we identify a series of burning questions and grand challenges associated with their continuing development and integration. We then discuss potential pathways towards solving these challenges, grouped by strategical, technical and collaborative developments. This paper is not intended to be a review, but rather to motivate and direct future research and collaboration across typically distinct fields based on \textit{community driven input}, to encourage further progress in our understanding of circumstellar and protoplanetary discs.

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arXiv2016

On the maximum grain size entrained by photoevaporative winds

We model the behaviour of dust grains entrained by photoevaporation-driven winds from protoplanetary discs assuming a non-rotating, plane-parallel disc. We obtain an analytic expression for the maximum entrainable grain size in extreme-UV radiation-driven winds, which we demonstrate to be proportional to the mass loss rate of the disc. When compared with our hydrodynamic simulations, the model reproduces almost all of the wind properties for the gas and dust. In typical turbulent discs, the entrained grain sizes in the wind are smaller than the theoretical maximum everywhere but the inner disc due to dust settling.

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arXiv2016

On dust entrainment in photoevaporative winds

We investigate dust entrainment by photoevaporative winds in protoplanetary discs using dusty smoothed particle hydrodrodynamics (SPH). We use unequal-mass particles to resolve more than five orders of magnitude in disc/outflow density and a one-fluid formulation to efficiently simulate an equivalent magnitude range in drag stopping time. We find that only micron sized dust grains and smaller can be entrained in EUV driven winds. The maximum grain size is set by dust settling in the disc rather than aerodynamic drag in the wind. More generally, there is a linear relationship between the base flow density and the maximum entrainable grain size in the wind. A pileup of micron sized dust grains can occur in the upper atmosphere at critical radii in the disc as grains decouple from the low-density wind. Entrainment is a strong function of location in the disc, resulting in a size sorting of grains in the outflow---the largest grain being carried out between $10$--$20\,$AU. The peak dust density for each grain size occurs at the inner edge of its own entrainment region.

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arXiv2016

A Plane-Parallel Wind Solution For Testing Numerical Simulations of Photoevaporation

Here we derive a Parker-wind like solution for a stratified, plane-parallel atmosphere undergoing photoionisation. The difference compared to the standard Parker solar wind is that the sonic point is crossed only at infinity. The simplicity of the analytic solution makes it a convenient test problem for numerical simulations of photoevaporation in protoplanetary discs.

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