Exoplanets: What, Why, How, Now, and What Next

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Exoplanets What, Why, How, Now, and What Next?

• Tim Morton,
• California Institute of Technology
• Letenka 2009

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What is an Exoplanet?

• Exoplanet is short for Extra-solar planet,
  meaning a planet orbiting a star other than our
  sun.
• First exoplanet (Peg 51) discovered in 1995
• Jupiter-like, 4-day orbit
• Today, 358 known (282 within 200 pc and
  well-characterized)
• Check out exoplanets.org or exoplanets.eu for
  current stats
• One of the most exciting topics in astronomy!

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Why do we care?

• Fundamental motivation Are we alone in the
  Universe?
• Easier question Are there planets around other
  stars that can possibly support life?
• Two ways to approach this question
• Find other planets that can support life (i.e.
  liquid water)
• Ask the question How common are planetary
  systems like our Solar System?

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Habitable Zone
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How are exoplanets found?

• Direct detection (lt10) Look directly for light
  coming to us from exoplanets
• Indirect methods (gt300) see the effects of a
  planets presence by looking at stars
• Wobbles (Radial Velocity, Astrometry)
• Blinks (Transits, Microlensing)
• (Why is direct detection so hard?)

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Direct Detection
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Indirect Detection

• Use wobbles and blinks to try to infer
  characteristics of exoplanets
• Existence!
• Mass (M)
• Distance from host star (a)
• Radius (densityrocky or gas?) (R)
• Atmosphere composition? (Life?)
• Different methods can determine different
  characteristics

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The Wobble
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The Wobble

• Radial Velocity
• Relies on Doppler effect (demonstration)
• Gives Msin(i) (orbit orientation unknown)
• Gives separation
• Most exoplanets so far discovered with this
  method
• Astrometry
• Relies on very accurate position measurements of
  host star
• Gives M,a, independent of inclination!
• Very hard! (But first one just found this year)
• Best chance to find an earth around a nearby
  sun-like star (with a space mission)!

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The Blink

• Transits
• Simple concept (demonstration)
• Gives M, a, radius (density), and maybe much
  more! (exciting follow-up possible)
• 25 exoplanets found this way
• Have to be lucky!
• Microlensing
• More complicated
• Get M, a, but no follow-up possible

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Transits
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The Blink

• Transits
• Simple concept (demonstration)
• Gives M, a, radius (density), and maybe much
  more! (exciting follow-up possible)
• 25 exoplanets found this way
• Have to be lucky!
• Microlensing
• More complicated
• Get M, a, but no follow-up possible

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Microlensing
Gravity bends light (video)
Animations by Scott Gaudi, Ohio State University
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The Blink

• Transits
• Simple concept (demonstration)
• Gives M, a, radius (density), and maybe much
  more! (exciting follow-up possible)
• 25 exoplanets found this way
• Have to be lucky!
• Microlensing
• More complicated
• Get M, a, but no follow-up possible

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Now What have we found?

• Mostly Hot Jupiters
• Recently, more Neptunes and Super-Earths

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Now What have we found?

• Mostly Hot Jupiters
• Recently, more Neptunes and Super-Earths

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Exciting News!
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Major current (and future) projects

• Radial Velocity
• Ongoing long-term ground-based monitoring of
  sun-like stars
• Monitoring of M-dwarfs (like Gliese 581)
• Transits
• HATNet (ground-based small telescope network)
• Kepler (space-based, launched earlier this year!)
• MEarth (ground-based M-dwarf transit search,
  coming online now)
• Targeted follow-up of RV-discovered planets (me!)
• Microlensing
• Ongoing ground-based searches
• Future space-based missions planned
• Direct Imaging
• Continuing search for wide-separation planets
• Astrometry
• Space Interferometry Mission (10 years?)

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HATNet
Automated network of small (10cm) telescopes
around the world looking for transits around
bright stars
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Kepler

• Will stare at the same 100,000 stars
  continuously for 5 years
• Will be able to discover Earths transiting
  stars like our Sun

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Kepler First Light!
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MEarth project Mt. Hopkins, AZ

• Goal monitor large numbers of M-dwarf stars to
  look for transiting planets
• Remember, M-dwarfs have close habitable zones
  (like Gliese 581)

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Space Interferometry Mission
Will measure positions of stars very precisely
will be able to detect wobbles caused by
earth-sized planets around nearby stars!
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Microlensing Planet Finder?
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Different methods find different planets
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What Next? (Future!)

• Surveys will establish good statistics of
  exoplanetary systems
• Many habitable zone planets will be found
• SIM especially will find HZ planets around nearby
  stars
• Targeted follow-up observations will be able to
  characterize exoplanet atmospheres
• Find signatures of life?
• Targeted SETI communication?

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Maybe soon?