arXiv subjects

Teng Ee Yap

Publications and source records attributed to Teng Ee Yap.

6 recordsLinked to original sources

arXiv2026

Formation of Water-rich Giant Planet Satellites at Decretion Disk Ice Lines

The volatile budgets of giant planet satellites are critical to unraveling the origin of their building blocks within the circumplanetary disks that hosted them. The Galilean moons Ganymede and Callisto, as well as the Saturnian moon Titan, are known to be anomalously water rich on the basis of their mean densities and interior models informed by gravity data from Galileo and Cassini, characterized by ice-to-rock ratios around unity. Here, we show that the water-ice sublimation line in a decreting circumplanetary disk lends itself to the formation of a water-rich solid reservoir, serving as a natural site for the birthplace of icy satellites. Fundamentally, this reflects how interior to the ice line, water vapor is advected outward, while beyond it, water ice drifts inward as pebbles. Using a semi-analytic model for dust and vapor evolution, we simulate vapor and ice accumulation at the ice line, showing that solids just beyond it achieve steady-state ice-to-rock ratios a factor of a few higher than elsewhere in the disk. For typical disk parameters, this ice buildup occurs within a timescale of a few thousand years. We propose this as a first-order process that explains, at least to some extent, the compositions of three aforementioned satellites. We explore the impact of uncertain turbulence parameters on our results, namely the turbulent Schmidt number and Shakura-Sunyaev alpha, before discussing them in the context of icy satellite D/H ratios. We conclude by evaluating alternative scenarios for explaining water-rich satellites, based on the conversion of CO to CH4, with water as a by-product.

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arXiv2026

Callisto's Nonresonant Orbit as an Outcome of Circum-Jovian Disk Substructure

The Galilean moons of Io, Europa, and Ganymede exhibit a 4:2:1 commensurability in their mean motions, a configuration known as the Laplace resonance. The prevailing view for the origin of this three-body resonance involves the convergent migration of the moons, resulting from gas-driven torques in the circum-Jovian disk wherein they accreted. To account for Callisto's exclusion from the resonant chain, a late and/or slow accretion of the fourth and outermost Galilean moon is typically invoked, stalling its migration. Here, we consider an alternative scenario in which Callisto's nonresonant orbit is a consequence of disk substructure. Using a suite of N-body simulations that self-consistently account for satellite-disk interactions, we show that a pressure bump can function as a migration trap, isolating Callisto and alleviating constraints on its timing of accretion. Our simulations position the bump interior to the birthplaces of all four moons. In exploring the impact of bump structure on simulation outcomes, we find that it cannot be too sharp nor flat to yield the observed orbital architecture. In particular, a "Goldilocks" zone is mapped in parameter space, corresponding to a well-defined range in bump aspect ratio. Within this range, Io, Europa, and Ganymede are sequentially trapped at the bump, and ushered across it through resonant lockstep migration with their neighboring, exterior moon. The implications of our work are discussed in the context of uncertainties regarding Callisto's interior structure, arising from the possibility of non-hydrostatic contributions to its shape and gravity field, unresolved by the Galileo spacecraft.

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arXiv2025

Infall and Disk Processes - the Message from Meteorites

How do planetary systems, in general, and our own Solar System (SS), in particular, form? In conjunction, Astronomy and Isotope Cosmochemistry provide us with powerful tools to answer this age-old question. In this contribution, we review recent advances in our understanding of circumstellar disk evolution, including infall and disk processes, as explored through astrophysical models and nucleosynthetic isotope anomalies of SS materials. Astronomically, filamentary structures and anisotropy are observed across the dynamic range of star formation and disk substructures are found to be ubiquitous, highlighting how star- and planet-forming environments are far more complex and dynamic than previously thought. Isotopically, two decades of investigation of nucleosynthetic anomalies in bulk meteorites and refractory inclusions have produced a rich dataset, revealing the existence of pervasive heterogeneity in the early SS, both at the large- (i.e., NC-CC dichotomy) and fine-scale (i.e., trends within the NC group). Using an updated data compilation, we review the systematics and emerging structures of these anomalies as a function of their nucleosynthetic origin. We present the two main families of models - inheritance vs. unmixing - that have been proposed to explain the origin of the observed isotope heterogeneities, and discuss their respective implications for cloud infall and thermal processing in the disk. We also discuss how the extension of nucleosynthetic anomaly analyses to other chondritic components (Ameboid Olivine Aggregates, chondrules, matrix) has started to yield insights into transport, processing and mixing of dust in the disk. Limitations, open questions and key avenues for future work are presented in closing.

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arXiv2024

Early Solar System Turbulence Constrained by High Oxidation States of the Oldest Non-Carbonaceous Planetesimals

Early Solar System (SS) planetesimals constitute the parent bodies of most meteorites investigated today. Nucleosynthetic isotope anomalies of bulk meteorites have revealed a dichotomy between non-carbonaceous (NC) and carbonaceous (CC) groups. Planetesimals sampling NC and CC isotopic signatures are conventionally thought to originate from the "dry" inner disk, and volatile-rich outer disk, respectively, with their segregation enforced by a pressure bump close to the water-ice sublimation line, possibly tied to Jupiter's formation. This framework is challenged by emerging evidence that the oldest NC planetesimals (i.e., the iron meteorites parent bodies; IMPBs) were characterized by far higher oxidation states than previously imagined, suggesting abundant ($\gtrsim$ few wt.%) liquid water in their interiors prior to core differentiation. In this paper, we employ a model for a degassing icy planetesimal (heated by $^{26}$Al decay) to map the conditions for liquid water production therein. Our work culminates in threshold characteristic sizes for pebbles composing the said planetesimal, under which water-ice melting occurs. Adopting a model for a disk evolving under both turbulence and magnetohydrodynamic disk winds, and assuming pebble growth is fragmentation-limited, we self-consistently translate the threshold pebble size to lower limits on early SS turbulence. We find that if NC IMPBs were "wet," their constituent pebbles must have been smaller than a few centimeters, corresponding to typical values of the Shakura-Sunyaev $α_ν$ turbulence parameter in excess of $10^{-3}$. These findings argue against a quiescent SS disk (for <10 AU), are concordant with astronomical constraints on protoplanetary disk turbulence, and suggest pebble accretion played a secondary role in building our rocky planets.

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arXiv2024

Dust-Gas Coupling in Turbulence- and MHD Wind-Driven Protoplanetary Disks: Implications for Rocky Planet Formation

The degree of coupling between dust particles and their surrounding gas in protoplanetary disks is quantified by the dimensionless Stokes number. The Stokes number (St) governs particle size and spatial distributions, in turn establishing the dominant mode of planetary accretion in different disk regions. In this paper, we model the characteristic St of particles across time in disks evolving under both turbulent viscosity and magnetohydrodynamic (MHD) disk winds. In both turbulence- and wind-dominated disks, we find that collisional fragmentation is the limiting mechanism of particle growth, and the water-ice sublimation line constitutes a critical transition point between dust settling, drift, and size regimes. The St dichotomy across the ice-line translates to distinct planet formation pathways between the inner and outer disk. While pebble accretion proceeds slowly for rocky embryos within the ice-line (across most of parameter space), it does so rapidly for volatile-rich embryos beyond it, allowing for the growth of giant planet cores before disk dissipation. Through simulations of rocky planet growth, we evaluate the competition between pebble accretion and classical pairwise collisions between planetesimals. We conclude that the dominance of pebble accretion can only be realized in disks that are driven by MHD winds, slow-evolving, and devoid of pressure maxima that may concentrate solids and give rise of planetesimal rings. Such disks are extremely quiescent, with Shakura-Sunyaev turbulence parameters $α_ν \sim 10^{-4}$. We conclude that for most of parameter space corresponding to values of $α_ν$ reflected in observations of protoplanetary disks ($\gtrsim 10^{-4}$), pairwise collisions constitute the dominant pathway of rocky planet accretion. Our results are discussed in the context of super-Earth origins and Earth's accretion history.

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arXiv2021

The Macroporosity of Rubble Pile Asteroid Ryugu and Implications for the Origin of Chondrules

We use the known surface boulder-size distribution of the C-type rubble pile asteroid Ryugu (NEA 162173) to determine its macroporosity, assuming it is a homogeneous granular aggregate. We show that the volume-frequency distribution of its boulders, cobbles and pebbles, is well represented by a lognormal function with $σ= 2.4 \pm 0.1$ and $μ= 0.2 \pm 0.05$. Application of linear-mixture packing theory yields a value for the macroporosity of $ϕ= 0.14 \pm 0.04$. Given its low bulk density of 1.19 gm cm$^{-3}$, this implies an average density for Ryugu's rocks of $1.38 \pm 0.07$ gm cm$^{-3}$ throughout its volume, consistent with a recent determination for surface boulders based on their thermal properties. This supports the spectrum-based argument that IDP's may be the best analog material available on Earth and suggests that high-density, well-lithified objects such as chondrules and chondrule-bearing chondrites may be rare on Ryugu. Implications of this result for the origin of chondrules, a long-standing problem in cosmochemistry, are discussed. We propose that chondrules and most chondrites formed together in rare lithification events, which occurred during the accretion of chondritic envelopes to large, differentiated planetesimals at a time when they were still hot from $^{26}$Al decay.

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