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Other “Solar” Systems
Exoplanets
• Planets beyond the Solar System orbiting a star other than the Sun
• First exoplanet discovered in 1992 through a pulsar timing method: PSR B1257+12 B
• First exoplanet discovered using radial velocity was 51 Pegasi b in 1995
• Current count: 424 (as of January 13, 2010 according to the
Extra-solar Planets Encyclopedia)
What are some things that we know about planetary systems that might
help us find exoplanets?• What methods could we use to find
planets around other stars?
Why is it difficult to directly observe an exoplanet?
Methods of Detecting Exoplanets
• Astrometry
• Radial Velocity
• Microlensing
• Timing
• Imaging
• Transit
Astrometry Method
• Precise measurements of how a star’s position in the sky changes over time
• If there is a planet present then gravitational influences will cause the star to move in tiny circular or elliptical orbits
• Using the distance to the star, mass of the star and how much it moves in the sky, the mass and distance to the planet(s) can be calculated
Radial Velocity Method
• (Doppler Method) Astrometry from an edge-on view
• Variations in the radial velocity of a star causes shifts in the star’s spectral lines
• The amount of shift in the spectral lines determines how fast the star is moving
• If we know how fast the star is moving and its period, the mass and distance to the planet(s) can be calculated
• Variations down to 1 m/s can be detected with modern spectrometers
Microlensing
• Gravitational field of a star acts like a lens which causes a background star to appear brighter than it typically is
• A planet’s gravitational field can add to this effect
Direct Imaging
• Image that shows a planet next to a star
• May be possible when the planet is very large, orbits at a great distance and young (emits more infrared radiation)
Transit Method
• If a planet crosses in front of the star’s disk, the amount
of light we receive from the star drops a small amount
• Radius and period of the planet can be determined and
when combined with the radial velocity method, the
mass and density of the planet can be calculated
• By studying the high resolution stellar spectrum,
elements in the planet’s atmosphere can be detected
• Temperature can also be determined using this method
Transit of Venus across the Sun
Methods of Detecting Exoplanets
• Radial Velocity/Astrometry– 401 planetary systems– 475 planets– 47 multiple planet systems
• Microlensing– 10 planetary systems– 11 planets– 1 multiple planet systems
• Imaging-- 11 planetary systems– 14 planets – 1 multiple planet system
• Timing– 6 planetary systems– 10 planets– 3 multiple planet systems
•Transiting •109 planetary systems•111 planets• 7 multiple planet systms
•Current count: 510 (as of December 16, 2010 according to the Extra-solar Planets Encyclopedia) Increase of 87 from one year ago.
Habitability
What is needed for life?
Habitability
NASA has defined principal habitability
criteria as “extended regions of liquid
water, conditions favorable for the
assembly of complex organic molecules,
and energy sources to sustain
metabolism.”
The Habitable Zone
“Goldilocks Zone”
The habitable zone is a theoretical area surrounding a star in which liquid water
could exist on the planet’s surface.
Not too close, not too far, just right.
Exoplanet Encyclopedia:www.exoplanet.eu
NASA’s Kepler Mission:www.kepler.nasa.gov
Habitable Planets activity:www.kepler.nasa.gov/ed/pdf/HabitablePlanets.pdf
