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Theses

The magmatic crust of Vesta

Abstract : Asteroids Vesta and Ceres motivated the space mission Dawn because they represent two different planetary embryos that remained relatively intact since their formation. Vesta is broadly considered as the parent body of the HED meteorites suite that are witnesses of a magmatic activity probably due to the presence of the radioactive isotope 26 Al which was present in significant amount to cause internal melting of primitive rocky bodies. The composition of a planetary surface can be quantified through the analysis of the gamma rays it produces. This is made possible for the Dawn spacecraft by the instrument GRaND and the scintillation of a BGO crystal. This thesis presents the analysis of gamma ray spectra from Vesta by two blind source separation methods: the independent component analysis and the non negative matrix factorization. These methods are also applied to an equivalent lunar dataset already well interpreted. Lunar synthetic spectra are used to test ICA and NMF. The separation of elementary spectra is delicate although K, Th and Fe can be discriminated due to the more favorable statistical properties of their source signals. The sensitivity of separation to the chemical variability is assessed based on artificial lunar spectra, which allows to explain the lack of separation of a clear elemental signal in the case of Vesta. Despite the observations of Dawn and the important collection of HED data, there is no consensus on the conditions of the vestan magmatism. A global magma ocean is often put forward, whereas the migration of the heat source, contained in the easiest mineral to melt, plagioclase, does not allow it. A model of melt migration is implemented, based on two-phase flow equations. This model is combined with the olivine-anorthite-quartz equilibrium phase diagram. This allows to predict the mineralogy as a function of depth and time. Results obtained show that eucrites and diogenites may be a common feature of large bodies accreted early in solar system history.
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Submitted on : Tuesday, October 20, 2015 - 2:36:50 PM
Last modification on : Friday, October 23, 2020 - 4:52:05 PM
Long-term archiving on: : Friday, April 28, 2017 - 6:10:04 AM

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  • HAL Id : tel-01218021, version 1

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Citation

Hugau Mizzon. The magmatic crust of Vesta. Earth and Planetary Astrophysics [astro-ph.EP]. Universite Toulouse III Paul Sabatier, 2015. English. ⟨tel-01218021⟩

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