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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

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

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

Extrasolar hot jupiters vs our jupiter
ExtrasolarHot Jupitersvs. Our Jupiter

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!