Extrasolar Planets
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  • 1. Extrasolar Planets
  • 2. Discovery of other planets In 1995 Michel Mayor and Didier Queloz of the Geneva Observatory discovered a planet orbiting the star 51 Pegasi, 50 ly away. Their results were confirmed by Geoff Marcy and Paul Butler using California’s Lick Observatory. They used the radial velocity method to detect the planet.
  • 3. Methods of detection Ways of detecting extrasolar planets: 1 Astrometric method 2 Radial velocity method 3 Transit method
  • 4. Astrometric method As a planet orbits a star it pulls on the star making it wobble. The astrometric method involves making very precise measurements (accuracy of at least 0.001”) of a star’s position in the sky relative to other stars. If they have an orbiting planet their position changes in a periodic way. The Hubble Space Telescope used astrometry to discover a planet around star Gliese 876 in 2002.
  • 5. Radial velocity method Based on the Doppler effect; a star wobbling due to an orbiting planet will periodically move towards and away from the Earth. Absorption lines in it’s spectrum will shift to the blue and the red in a cyclic fashion. These shifts are very small as the star’s motion around it’s orbit is very slow, so high resolution instruments are needed to detect this. Velocity variations down to 1 m s-1 can be detected with spectrometers such as HARPS (High Accuracy Radial Velocity Planet Searcher) at the ESO La Silla Observatory in Chile, or HIRES at the Keck Observatory in Hawaii.
  • 6. Transit method This method looks for a drop in stellar brightness as a planet crosses in front (transits). The extent of the drop depends on the relative sizes of the star and the planet. For this method to work the orientation of the planet’s orbit has to be aligned with our line-of- sight for us to see a transit. Also results often have to be confirmed by radial velocity measurements. The Spitzer Space Telescope was used to study variations in brightness of the star HD 209458 which dims by up to 1.7%.
  • 7. Searching for extrasolar planets Hubble survey called the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS) took place in Feb 2004. Looked at 180 000 stars in the nuclear bulge 26 000 ly away. ESA COROT launched Dec 27 2006: using transit method, able to detect planets a few times to several times larger than the Earth. NASA Kepler mission launched March 7 2009: using transit method to scan 100 000 stars in the constellation of Cygnus. It is sensitive enough to detect planets smaller than Earth. NASA Space Interferometry Mission scheduled for 2014 will use astrometry. ESA Darwin probe scheduled for 2013 will image planets directly. NASA New Worlds Mission will use an occulter to block the star’s light so we are able to observe the planets.
  • 8. Searching for extrasolar planets http://www.nasa.gov/mission_pages/hubble/science/exoplanet_transit.html http://www.kepler.nasa.gov http://www.esa.int/science/darwin
  • 9. Planets detected 327
  • 10. Vulpecula α
  • 11. Artist’s impression HD 189733b Spectral Type: K1 - K2V (orange dwarf star) Distance: 63 ly An extrasolar planet was discovered orbiting HD 189733b; observers in France saw the planet transiting across the face of the star. It has an orbital radius of ~ 0.031 AU and a period of 2.219 days. The planet has a mass of 1.15 x mass Jupiter.
  • 12. Pegasus β α
  • 13. Artist’s impression 51 Pegasi Spectral Type: G2.5IVa or G4-5Va (yellow dwarf star) Apparent magnitude: 5.49 Distance: 50.1 ly Luminosity: 1.3LS Mass: 1.06MS Radius: 1.4RS Temperature: 5665 K 51 Pegasi is a star similar to the Sun that has an orbiting planet (discovered in 1995). The planet has a mass of 0.5 x Jupiter and orbits close to the star at a distance of 0.051 AU with a period of only 4.2 days.
  • 14. http://radmila-topalovic.blogspot.com