Hakim, K.

English

Approximately one-third of about four thousand known exoplanets are possibly rocky in nature. The chemical and physical diversity of rocky exoplanets is well beyond that of the rocky planets of our solar system; Mercury, Venus, Earth, and Mars. In this thesis, we investigate the mineralogy, structure, evolution, and habitability of rocky exoplanets by implementing laboratory and computational tools from geosciences. We derive a new ab initio equation of state of iron using density functional theory valid at and beyond the core pressures of super-Earths. We show that extrapolations of equations of state to pressures beyond their validity range result in significant errors in estimating the interior properties of planets. We perform high-pressure high-temperature experiments on chemical mixtures representative of the bulk composition of carbon-rich rocky exoplanets and find that graphite (and diamond, depending on pressure) is the dominant carbon-bearing mineral. Such exoplanets likely contain an iron-rich core, a silicate mantle, and a graphite outer shell. We also show that silicon carbide, another carbon-bearing mineral thought to be an important constituent of these exoplanets, is stable only if all oxidized iron in the planetary interior is reduced to its metallic state. Using a parameterized mantle convection model, we compute the thermal evolution of rocky exoplanets with a graphite outer shell and find that the graphite shell exhibits a thermal shielding effect resulting in a slower cooling of the planet. A priori these graphite-shell exoplanets are likely uninhabitable because of a lack of life-building elements at their surface other than carbon, however thin graphite shells might still allow habitability

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UvA-DARE is a service provided by the library of the University of Amsterdam (https://dare.uva.nl)UvA-DARE (Digital Academic Repository)Diving deep into rocky exoplanetsHakim, K.Publication date2018Document VersionOther versionLicenseOtherLink to publicationCitation for published version (APA):Hakim, K. (2018). Diving deep into rocky exoplanets. [Thesis, fully internal, Universiteit vanAmsterdam].General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s)and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an opencontent license (like Creative Commons).Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, pleaselet the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the materialinaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letterto: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. Youwill be contacted as soon as possible.Download date:09 Mar 2023Propositions belonging to this thesis DIVING DEEP INTO ROCKY EXOPLANETS 1. Laboratory and computational tools from geosciences enable studies of the interior and surface properties of rocky exoplanets for which little astronomical data are available (Chapters 2, 3, 4 and 5). 2. The chemical composition of rocky planets is capable of strongly influencing their interior and surface properties such as the physical structure, mineralogy, and evolution as well as their potential for habitability (Chapters 2, 3, 4 and 5). 3. Extrapolations of the equation of state to pressures beyond the validity range of the equation of state result in significant errors in estimating the interior properties of planets (Chapter 2). 4. Rocky exoplanets containing more than of the order of one percent carbon would contain carbon in the form of graphite. If these planets are fully differentiated, graphite will form an outer shell (Chapter 3). 5. Silicon carbide can be a dominant carbon-bearing mineral in a rocky exoplanet only if a complete reduction of Fe2+ and Fe3+ to Fe0 takes place (Chapter 4). 6. A graphite outer shell produces a thermal shielding effect which delays the cooling of a rocky planet (Chapter 5). 7. A graphite shell might, due to the lack of life-building elements other than carbon, make the planetary surface inhospitable for life (Chapter 3). A thick graphite shell would likely limit the potential for habitability more than a thin graphite shell (Chapter 5). 8. Interdisciplinary research requires more than just the expertise of two disciplines; it also requires the integration of two different scientific approaches. Establishing exogeoscience as a distinct discipline is the need of the hour to take significant strides in exoplanetary science. 9. Exoplanetary science is a rapidly expanding science which is generating a lot of interest among the public as well as funding agencies. With great power comes great responsibility. 10. Scientists and publishers should come together for once and decide to either follow British or American spellings for scientific articles. 11. The human aspect of a scientist’s life should never be disregarded. 12. Astronomy is poetry of science.  Kaustubh Hakim 

Diving deep into rocky exoplanets

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Diving deep into rocky exoplanets

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