other solar systems (12/16)
DESCRIPTION
TRANSCRIPT
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Other “Solar” Systems
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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)
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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?
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Why is it difficult to directly observe an exoplanet?
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Methods of Detecting Exoplanets
• Astrometry
• Radial Velocity
• Microlensing
• Timing
• Imaging
• Transit
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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
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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
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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
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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)
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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
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Transit of Venus across the Sun
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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.
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Habitability
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What is needed for life?
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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.”
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The Habitable Zone
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“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.
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Exoplanet Encyclopedia:www.exoplanet.eu
NASA’s Kepler Mission:www.kepler.nasa.gov
Habitable Planets activity:www.kepler.nasa.gov/ed/pdf/HabitablePlanets.pdf