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Astrophysical Impacts on Habitable Planetary Systems Kokaia, Giorgi Astrophysical impacts on habitable planetary systems Kokaia, Giorgi 2020 Link to publication Citation for published version (APA): Kokaia, G. (2020). Astrophysical impacts on habitable planetary systems. Lund University, Faculty of Science. 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LUND UNIVERSITY PO Box 117 221 00 Lund +46 46-222 00 00 Astrophysical impacts on habitable planetary systems Astrophysical impacts on habitable planetary systems Giorgi Kokaia Thesis for the degree of Doctor of Philosophy Thesis advisors: Prof. Melvyn B. Davies, Dr. Alexander J. Mustill Faculty opponent: Dr. Alessandro Sozzetti To be presented, with the permission of the Faculty of Science of Lund University, for public criticism in the Lundmark lecture hall (Lundmarksalen) at the Department of Astronomy and Theoretical Physics on Friday, 4th of December 2020 at 13:00. Document name LUND UNIVERSITY DOCTORAL DISSERTATION Dept. of Astronomy & Theoretical Physics Date of issue Lund Observatory Box 4 04 December 2020 !"#$$% &&' Lund' !(eden Author(s) Sponsoring organization Giorgi Kokaia Title and subtitle Astrophysical impacts on habitable planetary systems Abstract )indin* life on a planet other than the "arth (ould easily be one of the *reatest discoveries of all time' particularly so if it is found outside our !olar !ystem. To do so' (e must understand the conditions re+uired for life to emer*e and develop. ,hilst an enormous amount of research has *one into understandin* the re+uirements for life on "arth to have spontaneously arisen and then evolved' much less focus has been put on ho( factors outside the "arth and even outside the !olar !ystem may a-ect the so#called habitability of the "arth. This thesis summari.es three papers in (hich / have studied di-erent astrophysical e-ects that can impact the habitability of planets. /n Paper /' / investi*ate ho( the habitability of planets is a-ected by the 0alactic orbit of their host star by considerin* ho( often they encounter *iant molecular clouds. Paper / sho(s that for the !un these encounters and potential extinction events due to core#collapse supernovae happen rou*hly once per billion years. /n Paper //' / consider ho( planet#planet scatterin* bet(een *as *iants follo(in* an orbital instability can (ipe out habitable planets in a system. Paper // sho(s that in any exoplanet system (here there is an observed close#in eccentric *iant' it (ill be very unli1ely to 2nd any habitable planet. /n Paper ///' / examine ho( a system can be made uninhabitable if the host star pic1s up an additional planet durin* a close encounter (ith another star in its birth cluster. Paper /// sho(s that this can happen either by the ne( planet endin* up on an orbit that destabili.es the existin* planets in the system' or more interestin*ly' by si*ni2cantly increasin* the impact rate of lar*e asteroids for billions of years. Key words astrobiology; Sun: general; planetary systems; planets and satellites: dynamical evolution and stability Classification system and/or index terms (if any) Supplementary bibliographical information Language English ISSN and key title ISBN 345#3%#4536#73&#7 8print9 345#3%#4536#73%# 8pdf9 Recipient’s notes Number of pages Price 145 Security classification Distribution by Giorgi Kokaia, Dept. of Astronomy and Theoretical Physics, Box 43, SE-221 00, Lund Sweden. I, the undersigned, being the copyright owner of the abstract of the above-mentioned dissertation, hereby grant to all reference sources permission to publish and disseminate the abstract of the above-mentioned dissertation. Signature Date 2020-10-23 Astrophysical impacts on habitable planetary systems Giorgi Kokaia Faculty Opponent Dr. Alessandro Sozzetti University of Turin Turin, Italy Evaluation Committee Prof. Anja Andersen University of Copenhagen Copenhagen, Denmark Prof. Markus Janson Stockholm University Stockholm, Sweden Dr. Grant Kennedy University of Warwick Coventry, United Kingdom Cover – Image of NGC1333: a molecular cloud part of the Perseus complex, within it are embedded several young star clusters. Taken with a QSI 660wsg-8 camera mounted on a Takahashi FSQ106EDXIII refractor telescope from Abastumani, Georgia. Image credit: Reproduced with permission of David Dvali https://www.facebook.com/geoastro.net/ © Giorgi Kokaia 2020 Faculty of Science, Department of Astronomy and Theoretical Physics ISBN: 978-91-7895-690-6 (print) ISBN: 978-91-7895-691-3 (pdf) Printed in Sweden by Media-Tryck, Lund University, Lund 2020 Dedicated to my wife, Noemi Schaffer For being supportive and caring every evening and weekend I spent finishing this thesis Contents List of publications iii Popular summary v Populärvetenskaplig sammanfattning vii Acknowledgements ix I Research context 1 1 Planetary systems 5 1.1 Habitability . 5 1.2 Exoplanet observations . 7 1.3 Planetary dynamics . 10 2 Paper II 19 2.1 Introduction . 19 2.2 Sample used in Paper II . 20 2.3 Initial testing . 21 2.4 Numerical Experiment . 23 2.5 The History . 26 2.6 Selected systems . 28 3 Paper III 31 3.1 Introduction . 31 3.2 The SEjC system . 32 3.3 Generalizing farther . 36 ii CONTENTS 3.4 Effect on habitability . 39 4 Paper I 41 4.1 Introduction . 41 4.2 GMCs in the Galaxy . 44 4.3 Stellar orbits . 50 4.4 GMC encounter rates . 54 4.5 Consequences of GMC encounters . 55 4.6 Implications for the Sun . 59 II Research Papers 69 Paper I: Stellar encounters with Giant Molecular Clouds . 71 Paper II:Resilient habitability of nearby exoplanet systems . 91 Paper III: Effects of capturing a wide-orbit planet on planetary systems: system stability and Habitable Zone bombardment rates . 111 List of publications The following papers have been published as a result of my PhDwork: I Stellar encounters with Giant Molecular Clouds G. Kokaia, M.B. Davies (2019) Monthly Notices of the Royal Astronomical Society, Volume 498, Issue 1, p.5165-5180 II Resilient habitability of nearby exoplanet systems G. Kokaia, M.B. Davies, A.J. Mustill (2020) Monthly Notices of the Royal Astronomical Society, Volume 492, Issue 1, p. 352-368 III Effects of capturing a wide-orbit planet on planetary systems: system stability and Habitable Zone bombardment rates G. Kokaia, M.B. Davies, A.J. Mustill (2020) Submitted to Monthly Notices of the Royal Astronomical Society Not included in thesis: IV Oumuamuas passing through molecular clouds S. Pfalzner, M.B. Davies, G. Kokaia, M. Bannister (2020) Accepted, arXiv:2009.08773 iii Popular summary In this thesis the science in three of my published papers is presented. Each of the papers touches upon how astrophysical different phenomena can affect life on habitable planets in the Galaxy, where each paper addresses the question at a different scale. Going from largest to smallest, the work can be summarized as follows: On a Galactic scale, I investigated how often stars on different orbits cross through the spiral arms of the Galaxy where they can encounter large and dense gas clouds and supernovae. I found that its a very sensitive function of how old the star is and where in the Galaxy the star is located. With a star like the Sun encountering these things roughly once per billion years whereas younger stars located closer to the center of the Galaxy can have encounter rates more than 100 times larger. On the scale of stellar clusters, I examined the effects on habitable planets in a sys- tem whose host star picks up an additional planet during a close encounter with another star in its birth cluster. I found that in 60% of cases it will have a signif- icantly negative effect on the habitable planet, either by completely destroying it through dynamical interactions or by significantly enhancing the impact rate of large bodies on the planet. On the scale of a planetary system, I examined systems known to host gas giants and considered how dynamical instabilities and scattering between the observed giant planet and hitherto undetected / previously ejected gas giants in the systems’ past would have affected a planet in the habitable zone. I found that in most known systems a potential instability in the past would have wiped out a large fraction of planets in the habitable zone; in a small subset of systems this is not the case and they are presented as good candidates for future observations in the paper. v Populärvetenskaplig sammanfattning I den här avhandlingen är forskningen utförd i tre av mina publicerade artiklar beskriven. Var och en av artiklarna berör hur olika astrofysiska fenomen kan påverka liv på beboliga planeter i Galaxen. Tre olika problem, på tre olika skalor behandlas i respektive artikel. Från störst till minst skala kan arbetet summeras så här: På Galaktisk skala undersökte jag hur ofta stjärnors omloppsbanor tar dem genom Galaxens spiralarmar där de kan stöta på stora, tjocka gasmoln samt supernovor. Hur ofta detta sker visade jag vara en väldigt känslig funktion av stjärnans plats i Galaxen samt dess ålder.
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