We use a model of aerosol microphysics to investigate the impact of high-altitude photochemical aerosols on the transmission spectra and atmospheric properties of close-in exoplanets, such as HD 209458 b and HD 189733 b. The results depend strongly on the temperature profiles in the middle and upper atmospheres, which are poorly understood. Nevertheless, our model of HD 189733 b, based on the most recently inferred temperature profiles, produces an aerosol distribution that matches the observed transmission spectrum. We argue that the hotter temperature of HD 209458 b inhibits the production of high-altitude aerosols and leads to the appearance of a clearer atmosphere than on HD 189733 b. The aerosol distribution also depends on the particle composition, photochemical production, and atmospheric mixing. Due to degeneracies among these inputs, current data cannot constrain the aerosol properties in detail. Instead, our work highlights the role of different factors in controlling the aerosol distribution that will prove useful in understanding different observations, including those from future missions. For the atmospheric mixing efficiency suggested by general circulation models, we find that the aerosol particles are small (similar to nm) and probably spherical. We further conclude that a composition based on complex hydrocarbons (soots) is the most likely candidate to survive the high temperatures in hot-Jupiter atmospheres. Such particles would have a significant impact on the energy balance of HD 189733 b's atmosphere and should be incorporated in future studies of atmospheric structure. We also evaluate the contribution of external sources to photochemical aerosol formation and find that their spectral signature is not consistent with observations.

Les expériences de laboratoire ont montré que la photo-irradiation ultraviolette d'analogues de glaces astrophysiques suivie de leur réchauffement à température ambiante mène à la formation de résidus organiques réfractaires. Ces résidus, solubles dans l'eau, consistent en un riche mélange de composés organiques incluant entre autres des acides aminés, molécules potentiellement importantes pour la chimie prébiotique. Ces résidus sont considérés comme des analogues de la matière organique réfractaire que l'on pense être synthétisée sur les grains de poussière dans les nuages moléculaires et/ou dans les disques protoplanétaires, produit de l'évolution des glaces, et qui pourra être accrétée plus tard en comètes ou en astéroïdes et finalement délivrée sur la Terre primitive. Ainsi, l'étude de ces analogues, produits dans des conditions astrophysiques pertinentes, représente un outil efficace pour explorer les processus à l'origine de la formation des molécules organiques complexes dans le Système Solaire et en particulier la possible introduction d'excès énantiomériques dans les molécules chirales.Ce travail de thèse est consacré à l'étude de ces résidus organiques, leur caractérisation et les applications astrophysiques de ces résultats. Nous avons utilisé différentes techniques d'analyse comme la chromatographie en phase gazeuse couplée à la spectrométrie de masse (GC MS, classique et multidimensionnelle), la spectrométrie de masse par résonnance cyclotronique ionique à transformée de Fourier (FT ICR MS) ou encore la spectroscopie infrarouge. Nous avons mesuré les excès énantiomériques induits dans cinq acides aminés par irradiation de nos analogues avec de la lumière UV polarisée circulairement (UV CPL) et insérons nos résultats dans le cadre d'un scénario astrophysique cohérent pour expliquer l'origine des excès énantiomériques observés dans les acides aminés météoritiques. Nous avons étudié le contenu en acides aminés de la météorite de "Paris" et montré des similarités avec la distribution en acides aminés de nos résidus organiques. Nous avons également produit des analogues plus réalistes de grains interstellaires en incluant une surface silicatée, afin de tester l’effet potentiel de cette surface sur la formation et la nature des résidus organiques. Enfin, nous effectuons une discussion générale à propos de la pertinence de ces résultats dans le contexte astrophysique et soulignons le possible lien entre astrochimie et chimie prébiotique. / Laboratory experiments have shown that ultraviolet photo-irradiation of astrophysical ice analogs and their following warm-up until room temperature lead to the formation of refractory organic residues. These residues consist of rich mixtures of organic compounds, including amino acids, which have a potential importance for prebiotic chemistry. They are considered as analogs of the organic refractory materials that are thought to be synthesized on dust grains in molecular clouds and/or in protoplanetary disks, as a product of ices evolution, and that could be later accreted into comets and asteroids and eventually be delivered to the early Earth. Hence, the study of these analogs, produced under astrophysically relevant conditions, represents a valid tool to investigate the processes at work for the origin of complex organic molecules in the Solar System and in particular the possible introduction of enantiomeric excesses in chiral molecules. This PhD work is devoted to the study of these laboratory organic residues, their characterization and the astrophysical applications of the results. We used different analytical techniques such as gas chromatography mass spectrometry (GC MS, classical and multidimensional), Fourier transform ion cyclotron resonance mass spectrometry (FT ICR MS), and infrared spectroscopy. We measured the enantiomeric excesses induced in five chiral amino acids by UV circularly polarized light (UV CPL) irradiation of our analogs and insert our result in a coherent astrophysical scenario for the origin of the enantiomeric excesses observed in meteoritic amino acids. We studied the amino acid content of the Paris meteorite and evidence some similarities with the distribution of the amino acids in our organic residues. We also produced more realistic analogs of interstellar grains, including a silicate surface, to test the potential effect of such a surface on the formation and nature of organic residues. Finally, we discuss the significance of these results in the astrophysical context and the possible relationship between astrochemistry and prebiotic chemistry.

Indiana University-Purdue University Indianapolis (IUPUI) / This dissertation focuses on quantification of submicroscopic iron of different sizes, mineral abundance and grain size of lunar soils using Hapke's radiative transfer model. The main objective is to explore implications of these results for assessing the relative importance of solar wind implantation versus micrometeorite impacts for lunar space weathering as well as three hypotheses (solar wind deflection, comet impact and dust transport) for swirl formation on the Moon. Results from this study can help to make connections between ordinary chondritic meteorites and asteroids, and put physical and chemical constraints on heating processes in the early solar system.

<p>Space weathering refers to the gradual spectral, microstructural, and chemical alteration of airless planetary regoliths due to their exposure to the harsh environment of outer space. Solar wind irradiation and micrometeoroid impacts are the primary space weathering processes at work in our solar system. Although the microstructural and compositional effects of space weathering are small, occurring at the sub-micron scale in individual regolith grains, their collective impact on the spectral signature of planetary surfaces is critical. Space weathering is known to change the slope, albedo, and strength of absorption band features of reflectance spectra acquired by ground- and spacecraft-based instrumentation. In this way, space weathering impedes our ability to determine planetary surface compositions from remote sensing data and pair meteorites with their parent bodies. Thanks to decades of research since the Apollo sample return missions, the planetary science community has developed a comprehensive understanding of how space weathering alters the Moon and silicate-rich asteroids. However, the effects of space weathering on primitive, carbon-rich asteroids—which dominate the outer main belt—are more poorly constrained and very complex. This dissertation aims to improve our understanding of how solar wind irradiation and micrometeoroid bombardment modifies the spectral, microstructural, and chemical properties of carbonaceous asteroidal regoliths. To accomplish this goal, this research experimentally simulates constituent space weathering processes in the laboratory on carbon-rich analog materials. A multi-faceted analytical approach including a variety of electron microscopy and spectroscopic techniques is used to probe the spectral, microstructural, and chemical changes induced by experimental space weathering.</p><p>Chapter 1 of this dissertation provides an introduction to space weathering, including a description of the current state of knowledge in the field as well as the motivation for this research. Similarly, chapter 2 provides an overview of the various experimental simulations and coordinated analytical techniques employed in this work. Chapter 3 initiates the discussion of research accomplished during this doctoral program, presenting a detailed characterization of the spectral, microstructural, and chemical effects derived from simulated solar wind irradiation of a carbonaceous asteroid analog material. More specifically, in chapter 1, I perform high flux (~1013 ions/cm2/s), high fluence (1018 ions/cm2) 1 keV H+ and 4 keV He+ irradiation experiments on the Murchison meteorite. Chapter 2 investigates the role of incident ion flux in solar wind space weathering of carbonaceous asteroidal regolith by performing a set of low flux (~1011 ions/cm2/s) and high flux (~1013 ions/cm2/s) H+ and He+ irradiation experiments on Murchison samples. These experiments are the lowest flux solar wind simulations carried out, to date. Finally, chapter 5 presents results from the first <i>combined</i> ion irradiation and heating experiments performed on a carbon-rich analog using in situ transmission electron microscopy (TEM). In situ TEM is a relatively novel technique in the planetary and geological sciences which allows users to observe the physiochemical changes caused by an external stimuli in <i>real time</i>. The experimental approach used in chapter 5 simulates both solar wind irradiation and micrometeoroid impacts, and, thus, probes the cumulative microstructural and compositional modifications induced by these concurrent space weathering processes. In chapters 3 through 5, I compare my results to previous space weathering simulations and observations of lunar and asteroidal returned samples. Findings from this dissertation advance the existing model of space weathering on carbon-rich asteroids, help inform remote sensing observations from the Hayabusa2 and OSIRIS-REx missions which have rendezvoused with C-complex asteroids Bennu and Ryugu, respectively, and provide experimental ground-truth for analyzing returned samples from these missions.</p>

Orientadores: Álvaro Penteado Crósta, Ana Maria Góes / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências / Made available in DSpace on 2018-08-21T05:13:12Z (GMT). No. of bitstreams: 1 Maziviero_MarianaVelcic_M.pdf: 11852522 bytes, checksum: da3a2bbea2799f9f4339b2eec4ce7dcf (MD5) Previous issue date: 2012 / Resumo: Atualmente são conhecidas em toda superfície terrestre cerca de 180 estruturas formadas por impacto de meteoritos. No Brasil, foram diagnosticadas seis estruturas originadas por este tipo de evento: Araguainha (MT-GO), Vargeão (SC), Vista Alegre (PR), Cerro do Jarau (RS), Serra da Cangalha (TO) e Riachão (MA). A área de estudos é a estrutura de impacto de Riachão (7º43'S/46º39'W), uma estrutura de impacto do tipo complexa, ligeiramente elíptica, em avançado estágio erosivo e com diâmetro de aproximadamente 4 km. Esta estrutura situa-se na porção centro-oeste da Bacia do Parnaíba, onde predominam arenitos e, subordinadamente, rochas carbonáticas intercaladas com siltitos pertencentes à parte superior do Grupo Balsas depositados entre o Pensilvaniano e Permiano. Estudos geológicos dessa estrutura foram realizados nas décadas de 1960 e 1980, resultando na caracterização geológica preliminar da mesma. Neste trabalho, a partir da integração de dados geológicos e de sensoriamento remoto, foi possível caracterizar geológica e geneticamente a estrutura de Riachão. As unidades litoestratigráficas identificadas correspondem a diferentes níveis da Formação Pedra de Fogo, e, possivelmente, da Formação Piauí, diferenciando-se daquelas estabelecidas nos estudos prévios. O modo de ocorrência destas unidades em superfície é compatível com o modelo de estruturas complexas, no qual o núcleo soerguido exibe camadas mais antigas, circundadas por camadas mais jovens. Em relação às evidências de deformação por impacto foram identificadas rochas intensamente deformadas no interior da estrutura, deformação essa compatível com a origem por impacto meteorítico. Microscopicamente, foram descritas feições deformacionais tais como lamelas de Böhm, healed fractures, feather features, fraturas planares (PF), grãos extremamente fraturados e feições de deformação planares (PDF). Destas, apenas esta última é evidência definitiva da gênese por impacto meteorítico, tendo sido identificada em Riachão pela primeira vez. Com base na interpretação dos lineamentos interpretados a partir das imagens de sensores remotos e limites morfoestruturais de Riachão, sugere-se que a estrutura se formou por um impacto oblíquo com sentido de noroeste para sudeste. O modelo semiquantitativo elaborado permitiu inferir que, após a formação da estrutura, cerca de 280 m de espessura de rochas foram removidos por erosão, o que explica a ocorrência reduzida de indicadores de deformação por choque e/ou a aparente ausência de brechas de impacto e estruturas do tipo shatter cone / Abstract: At the present, about 180 meteorite impact structures have been identified on Earth. In the Brazilian territory, six structures of impact origin are known so far: Araguainha (MT-GO), Vargeão (SC), Vista Alegre (PR), Cerro do Jarau (RS), Serra da Cangalha (TO) and Riachão (MA). In this study, we focused on Riachão impact structure. This crater is located in Maranhão State of northeastern Brazil (S7º42', W46º38'). This semi-circular complex structure has a diameter of 4.2 km, and is in advanced state of erosion. The region containing the Riachão crater is located in central-west portion of the Parnaíba Basin. The strata in the Riachão area are part of the depositional sequence of the Balsas Group deposited between the Pensylvanian and Permian. The first geological studies on Riachão were made in 1960's and 1980's. In this work, by means of integrating geological field observation, petrographic examination of rock samples, and remote sensing data, we achieved a detailed geological and genetic characterization of the structure. The identified lithostratigraphic units consist of different levels of the Pedra de Fogo Formation, and, possibly, the Piauí Formation. This characterization is different from the one previously proposed. The exposure of such geological units is in accordance with models of complex structures, since the lower unit (Piauí Formation) is exposed at the central uplift, surrounded by the younger strata of the Pedra de Fogo Formation. Regarding macroscopic evidences of impact, we identified highly deformed rocks within Riachão structure exhibiting microscopic deformation features such as böhm lamellae, healed fractures, feather features, planar fractures (PF), fragmented grains and planar deformation features (PDF) were observed. PDF is an unequivocal microscopic shock-diagnostic evidence and its occurrence in Riachão is reported here for the first time. The lineament patterns and morphologic characteristics of the structure point towards a possible oblique impact with the impactor striking from northwest to southeast. We estimated the amount of rocks removed by erosion in the Riachão structure to be about 280 m. The absence of the crater-fill impact breccias, shatter cones, as well as the restricted occurrence of microscopic shock effects, are interpreted as the result of intense and relatively deep erosion after the formation of the initial crater / Mestrado / Geologia e Recursos Naturais / Mestre em Geociências

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This study presents an analysis of the organic matter in meteorites, particularly carbonaceous chondrites (CCs), using advanced experimental techniques such as Two-step laser desorption laser ionization mass spectrometry (L2MS-oTOF) and Atmospheric Pressure Photoionization-Orbitrap (APPI-Orbitrap). The analysis focuses on the molecular complexity of both soluble (SOM) and insoluble (IOM) organic matter as well as the bulk rock and identifying and classifying different molecular families to understand the chemical composition of the meteorites. A new software tool, SpectraC, was developed to aid in analysing and comparing mass spectra from multiple meteorite samples simultaneously. The findings of the study reveal the complex chemical composition of meteorites, with condensed aromatics dominating most samples, and highlight the importance of using multiple techniques for a more complete understanding of the sample’s contents. This research lays the foundation for future work in astrochemistry, including the development of a state-of-the-art analytical tool and further exploration of the organic matter in meteorites. / Cette étude présente une analyse de la matière organique dans les météorites, en particulier les chondrites carbonées (CC), en utilisant des techniques expérimentales avancées telles que la spectrométrie de masse à ionisation laser par désorption en deux étapes (L2MS-oTOF) et l’ionisation photochimique à pression atmosphérique-Orbitrap  (APPI-Orbitrap). L’analyse se concentre sur la complexité moléculaire de la matière organique soluble (SOM) et insoluble (IOM) ainsi que sur la roche globale, et identifie et classe différentes familles moléculaires pour comprendre la composition chimique des météorites. Un nouvel outil logiciel, SpectraC, a été développé pour aider à analyser et comparer les spectres de masse de plusieurs échantillons de météorites simultanément. Les résultats de l’étude révèlent la composition chimique complexe des météorites, avec une domination des aromatiques condensés dans la plupart des échantillons, et mettent en évidence l’importance d’utiliser plusieurs techniques pour une compréhension plus complète du contenu des échantillons. Cette recherche pose les bases des travaux futurs en astrochimie, y compris le développement d’outils analytiques de pointe et l’exploration plus poussée de la matière organique dans les météorites.