Devolatilization During the Formation of Rocky Planets: Bulk Elemental Composition

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dc.contributor.authorWang, Haiyangen_AU
dc.date.accessioned2018-11-29T22:55:57Z
dc.date.issued2018
dc.description.abstractAs the solar nebula condensed, evaporated and fractionated to form the nascent Earth, the bulk elemental composition of the Earth was established. To first order, the Earth is a devolatilized sample of the solar nebula. Similarly, rocky exoplanets are also likely devolatilized samples of the stellar nebulae out of which they and their host stars formed. If this assumption holds, we can estimate the chemical composition of rocky exoplanets by applying a devolatilization algorithm based on the elemental abundances of their host stars. This thesis is an investigation of this potentially universal devolatilization pattern, from which exoplanetary chemistry and habitability are then derived. To quantify (in broad terms) the chemical relationships between the Earth, the Sun and other bodies in the Solar System, the elemental abundances of the bulk Earth are required. The key to comparing Earth’s composition with those of other objects is to have a determination of the bulk composition with an appropriate estimate of un- certainties. We present concordance estimates (with uncertainties) of the elemental abundances of the bulk Earth, by compiling, combining, and renormalizing a large set of heterogeneous literature values of the primitive mantle and of the core. The weighting factor for the concordance estimates comes from our new estimate of the core mass fraction of the Earth: 32.5±0.3 wt% (weight percent). The uncertainties on our elemental abundances usefully calibrate the unresolved discrepancies between standard Earth models made under various geochemical and geophysical assump- tions. We then extend our assessment of terrestrial abundances to the modeling of pro- tosolar abundances based on the latest estimates of solar photospheric abundances and primitive meteoritic abundances. We compare our new protosolar abundances with our estimates of bulk Earth composition, thereby quantifying the devolatiliza- tion of the solar nebula that led to the formation of the Earth. As a function of elemental 50% condensation temperatures (TC), we fit the Earth-to-Sun abundance ratios f to the linear trend log( f ) = a log(TC ) + b. The best fit coefficients are: a = 3.676 ± 0.142 and b = 11.556 ± 0.436. The quantification of the slope a provides an empirical observation upon which modeling of the devolatilization processes can be based. These coefficients determine a critical devolatilization temperature for the Earth TD(E) = 1391 ± 15 K. The resultant devolatilization pattern allows inferences to be made concerning the depletions of elements in the early solar system and is potentially useful for estimating the chemical composition of rocky exoplanets from their known host stellar abundances. We apply the devolatilization pattern to nearby planetary systems to infer the bulk elemental composition of rocky exoplanets – particularly those within the cir- cumstellar habitable zones – from the known host stellar elemental abundances. The estimated bulk planetary composition (rather than the host stellar abundances) is then used as a principal constraint to model the interior composition and structure of such exoplanets. We apply these constraints to four planet host stars: Kepler-10, Kepler-20, Kepler-21 and Kepler-100, to model the interiors including the mantle and core compositions as well as core mass fraction for potential terrestrial exoplanets orbiting these host stars. With respect to the estimates of the interiors, we conclude that a potential terrestrial exoplanet orbiting Kepler-21 would be the most Earth-like while one orbiting Kepler-10 would be the least.en_AU
dc.format.extent1 vol.en_AU
dc.format.mimetypeapplication/pdfen_AU
dc.identifier.otherb58076669
dc.identifier.urihttp://hdl.handle.net/1885/153341
dc.language.isoen_AUen_AU
dc.provenancepermission to make it open was received via email on 30/03/2019
dc.publisherCanberra, ACT : The Australian National Universityen_AU
dc.rightsAuthor retains copyrighten_AU
dc.subjectdevolatilizationen_AU
dc.subjectdevolatilisationen_AU
dc.subjectvolatilityen_AU
dc.subjectvolatility trenden_AU
dc.subjectplanet formationen_AU
dc.subjectelemental compositionen_AU
dc.subjectchemical compositionen_AU
dc.subjectelemental abundanceen_AU
dc.subjectEarthen_AU
dc.subjectprimitive mantleen_AU
dc.subjectcoreen_AU
dc.subjectSunen_AU
dc.subjectsolar abundanceen_AU
dc.subjectproto-Sunen_AU
dc.subjectprotosolar abundanceen_AU
dc.subjectcondensationen_AU
dc.subjectevaporationen_AU
dc.subjectphotoevaporationen_AU
dc.subjectmeteoriteen_AU
dc.subjectchondriteen_AU
dc.subjectchondruleen_AU
dc.subjectexoplaneten_AU
dc.subjectextrasolar planeten_AU
dc.subjectrocky exoplaneten_AU
dc.subjectterrestrial exoplaneten_AU
dc.subjectinterioren_AU
dc.subjectinterior structureen_AU
dc.subjectmineralogyen_AU
dc.subjectconstrainten_AU
dc.subjectenhanced constrainten_AU
dc.subjecthabitabilityen_AU
dc.subjecthabitableen_AU
dc.subjectpale blue doten_AU
dc.titleDevolatilization During the Formation of Rocky Planets: Bulk Elemental Compositionen_AU
dc.typeThesis (PhD)en_AU
dcterms.accessRightsOpen Accessen_AU
dcterms.valid2018en_AU
local.contributor.affiliationResearch School of Astronomy and Astrophysics, ANU College of Scienceen_AU
local.contributor.authoremailhaiyang.wang@anu.edu.auen_AU
local.contributor.institutionThe Australian National Universityen_AU
local.contributor.supervisorLineweaver, Charles Hen_AU
local.contributor.supervisorcontactcharley.lineweaver@anu.edu.auen_AU
local.description.notesThe author has deposited the thesis.en_AU
local.description.refereedYesen_AU
local.identifier.doi10.25911/5d5147caa0d1e
local.mintdoimint
local.request.emailrepository.admin@anu.edu.auen_AU
local.request.nameDigital Thesesen_AU
local.type.degreeDoctor of Philosophy (PhD)en_AU

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