Abstract
AbstractModeling the planetary heat transport of small bodies in the early Solar System allows us to understand the geological context of meteorite samples. Conductive cooling in planetesimals is controlled by thermal conductivity, heat capacity, and density, which are functions of temperature (T). We investigate if the incorporation of the T‐dependence of thermal properties and the introduction of a nonlinear term to the heat equation could result in different interpretations of the origin of different classes of meteorites. We have developed a finite difference code to perform numerical models of a conductively cooling planetesimal with T‐dependent properties and find that including T‐dependence produces considerable differences in thermal history, and in turn the estimated timing and depth of meteorite genesis. We interrogate the effects of varying the input parameters to this model and explore the nonlinear T‐dependence of conductivity with simple linear functions. Then we apply non‐monotonic functions for conductivity, heat capacity, and density fitted to published experimental data. For a representative calculation of a 250 km radius pallasite parent body, T‐dependent properties delay the onset of core crystallization and dynamo activity by ∼40 Myr, approximately equivalent to increasing the planetary radius by 10%, and extend core crystallization by ∼3 Myr. This affects the range of planetesimal radii and core sizes for the pallasite parent body that are compatible with paleomagnetic evidence. This approach can also be used to model the T‐evolution of other differentiated minor planets and primitive meteorite parent bodies and constrain the formation of associated meteorite samples.
Highlights
Planetesimals are small rocky or icy bodies of a few to a few hundred kilometers in diameter that formed by collisional coagulation in the protoplanetary disk, and are considered the building blocks of larger planetary bodies (Kokubo & Ida, 2012; Weidenschilling, 2000)
For a representative calculation of a 250 km radius pallasite parent body, T-dependent properties delay the onset of core crystallization and dynamo activity by ∼40 Myr, approximately equivalent to increasing the planetary radius by 10%, and extend core crystallization by ∼3 Myr
Before we address the specific example of the pallasite parent body, we outline the approach used to incorporate T-dependent properties in models of conductive cooling of planetesimals and show how, even in simple cases, this can have an important influence on their thermal history
Summary
Planetesimals are small rocky or icy bodies of a few to a few hundred kilometers in diameter that formed by collisional coagulation in the protoplanetary disk, and are considered the building blocks of larger planetary bodies (Kokubo & Ida, 2012; Weidenschilling, 2000). Understanding the geological context of differentiated meteorites and their parent bodies' thermal evolution allows constraints to be placed on the formation, differentiation, and eventual breakup of planetesimals, and on the early evolution of the Solar System. In this context, models of conductive cooling of differentiated primary parent bodies are frequently used to aid the interpretation of meteorite samples. We use a pallasite parent body as an example to illustrate the influence that including T-dependent properties can have on understanding the origin of meteorite samples
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