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AST 111

AST 111. Exoplanets II. What can we measure?. Orbital period Look at doppler shift or just watch it Orbital distance Kepler’s 3 rd Law with orbital period Orbital shape Look at symmetry of doppler shift or just watch it Mass Need star’s orbital speed (about CM) Size

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AST 111

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  1. AST 111 Exoplanets II

  2. What can we measure? • Orbital period • Look at doppler shift or just watch it • Orbital distance • Kepler’s 3rd Law with orbital period • Orbital shape • Look at symmetry of doppler shift or just watch it • Mass • Need star’s orbital speed (about CM) • Size • Must come from transit • Density • Composition • Must come from transit

  3. The Count • 725 confirmed exoplanets (1-14-12) • 4 of these may be habitable

  4. Several “Super-Earths”have been discovered.These are a few timeslarger than Earth.

  5. Pending Confirmation • 2321 candidate exoplanets • 207 Earth-sized • 1181 Neptune-sized • 203 Jupiter-sized • 55 Larger than Jupiter • 48 are thought to be in the habitable zone • Two Earth-like planets found orbiting a Sun-like star!

  6. Estimates • 5.4% of all stars have Earth-like planets • 17% of all stars have multiple planets

  7. Notable Finds • Earth-sized planet around Proxima Centauri • Inside orbit of Mercury; not habitable • Cannonball Planet • 20x closer to parent star than Mercury is to Sun. Orbits in 0.84 days! • 1.4x larger than Earth and 4.6x more massive • Density similar to iron • 4-Planet system with 8 : 6 : 4 : 3 resonance • One planet orbiting two stars

  8. Extrasolar Planets vs. Solar System • Other solar systems seem to have both terrestrial and Jovian planets • Many observed exoplanets are “Hot Jupiters” • Close to parent stars • H-compounds would boil away • “Clouds of rock dust”

  9. Extrasolar Planets vs. Solar System • Hot Jupiters would actually glow! • The heat “inflates” the atmosphere • Lower density • Hot surface and rapid rotation lead to winds that create bands

  10. ExtrasolarHot Jupitersvs. Our Jupiter

  11. Formation of Other Solar Systems • Planetary migration: • “Hot Jupiters” formed in the outer solar system… • Migrated inward? • Waves can propagate through gaseous disk • Causes matter to bunch • Can pull on planets • Our Solar System: • Solar wind cleared out the gas before waves could happen

  12. Formation of Other Solar Systems • Nebular theory holding up well • Just by virtue of finding exoplanets • Planets should form more easily where there’s rock and ice • More planets found around stars that contain these ingredients • Some stars have “unusual assortment” in outer layers • THEY ATE THE PLANETS!

  13. Formation of Other Solar Systems • Challenges to nebular theory: • Jovian planets should only form past a frost line and have somewhat circular orbits • We see massive extrasolar planets on elliptical orbits close to stars

  14. Formation of Other Solar Systems • Elliptical orbits may be due to: • Close encounter between two large Jovian-like planets • One goes inward, the other goes outward • Orbital resonances

  15. Extrasolar Systems vs. Solar System • The planets in our Solar System more or less “ignore each other” • No orbital resonances • Other planetary systems’ planets interact strongly • Crowding and orbital resonances

  16. Exoplanet Hunters • Dedicated observatories being set up that will observe tens of thousands of star systems • Theoretically capable of spotting Earth-sized planets

  17. Kepler • Kepler • Orbits the Sun • Looks at constellation Cygnus • Will watch 145,000 stars • Can see transits of Earth-sized planets • Can see Mercury-sized planets for dimmer stars

  18. Telescopes in Formation • Interferometry uses multiple smaller telescopes to act like one big one • Astrometry would work: • Resolution of 1 micro-arcsecond • Could find Earth-sized planets around nearest dozen stars • Could find Jupiter-sized planets up to 3000 LY away!

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