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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

AST 111

Exoplanets II

what can we measure
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
the count
The Count
  • 725 confirmed exoplanets (1-14-12)
    • 4 of these may be habitable
pending confirmation
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!
  • 5.4% of all stars have Earth-like planets
  • 17% of all stars have multiple planets
notable finds
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
extrasolar planets vs solar system
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”
extrasolar planets vs solar system1
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
formation of other solar systems
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
formation of other solar systems1
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
formation of other solar systems2
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
formation of other solar systems3
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
extrasolar systems vs solar system
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
exoplanet hunters
Exoplanet Hunters
  • Dedicated observatories being set up that will observe tens of thousands of star systems
  • Theoretically capable of spotting Earth-sized planets
  • 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
telescopes in formation
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!