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The Search for Habitable Worlds

Explore the likelihood of finding habitable planets in our galaxy by analyzing the formation of stars and planets, evidence from HST, habitability zones, and the presence of water and carbon biomolecules. Discuss the relevance of factors such as planet size, atmospheric loss processes, greenhouse effect, and sources of energy for habitability.

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The Search for Habitable Worlds

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  1. The Search for Habitable Worlds A discussion of Bennett et al. Chapter 10 w/Prof. Geller

  2. Chapter Overview • Are Habitable Planets Common • Distant Stars • habitability zones • Extrasolar Planets • detection methodology • Signatures of Habitability and Life • Are Earth-like planets rare or common

  3. Are Habitable Planets Common? • Review formation of stars and planets • evidence from HST

  4. Habitability Zone Around Other Stars in Our Galaxy • Use the range from our solar system as a basis for analysis • In our solar system, 4 rocky planets that orbit the Sun from 0.4 to 1.4 AU and spaced 0.4 AU apart • If typical, likelihood of other solar systems having continuous habitability zone is just width of the zone divided by the typical spacing • 0.2/0.4 = 0.5 • Probability of 50% • Discuss this probability

  5. Habitability Zone in Our Galaxy • Other factors also relevant • Several stars in our galaxy with planets the size of Jupiter within terrestrial zone from their sun • Mass of star • Larger mass, greater luminosity, shorter life • Most abundant stars in galaxy are least luminous and longest-lived (red dwarfs)

  6. Habitability Zones Elsewhere in the Galaxy

  7. Another View of Habitability

  8. How to Find an Extrasolar Planet • Think about how a planet effects the star around which it orbits • light seen from star • gravitational effects • translate into visual effects • spectroscopic effects • translate into observed spectroscopic observations • remember Doppler Effect

  9. Four Ways to Find an Extrasolar Planet • Photometrically • light from star blocked by planet decreasing light seen from star in concert with orbit • Astrometrically • change in position caused by “dance with planet” • Spectroscopically • Doppler Effect on spectral lines due to “dance with planet” • Gravitational Microlensing • large gravitational force effecting light path

  10. Casting a Tiny Shadow

  11. Change in position of Sun due to Jupiter as seen from 10 parsecs distant

  12. Remember Doppler

  13. Applying Doppler

  14. Applying Einstein

  15. Extrasolar Planets Capability

  16. Considerations for Habitability • Distance from sun • Luminosity of sun • Planet size • Atmospheric loss processes • Greenhouse effect and gases in the atmosphere • Source of energy (internal/external) • Presence of water • Presence of carbon biomolecules • Biota

  17. Phases of Water and CO2

  18. Planetary Spectra

  19. Planet Size Questions • Tectonics: why important • Magnetosphere and solar winds • Gravity and tectonics

  20. Atmospheric Loss Processes to Consider • Solar winds of charged particles • Sweeps away atmosphere in episodic wind events • Planet’s magnetic field (magnetosphere) • Deflect solar winds • Earth and Mercury have magnetospheres • Mars and Venus do not have magnetospheres • Atmospheric loss processes • Escape velocity of gases

  21. Greenhouse Gases • Why is this relevant to habitability? Sources of Energy Why is this relevant to habitability? What are the sources of energy?

  22. Presence of Water • Is this relevant to the topic of habitability and if so what are the factors that are important? Presence of Carbon Biomolecules • Is this relevant to the topic of habitability and if so what are the factors that are important?

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