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Extra-Solar Planet Populations

Extra-Solar Planet Populations. George Lebo 10 April 2012 AST 2037. 1. Radial Velocity Planet Searches. So … need a speedometer to measure star velocity versus time To a precision of a few meters per second! Across distances of many light years!!!. How? Doppler shift of spectral lines.

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Extra-Solar Planet Populations

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  1. Extra-Solar Planet Populations George Lebo 10 April 2012 AST 2037 1

  2. Radial Velocity Planet Searches • So … need a speedometer to measure star velocity versus time • To a precision of a few meters per second! • Across distances of many light years!!! • How? Doppler shift of spectral lines 2

  3. 51 Pegasi • In 1995, Mayor & Queloz announce the discovery of an orbital signature with amplitude = 50 m/s in a 4.23-day period around star 51 Pegasi • Mass = 0.5 MJUP  First extra-solar planet 3

  4. 51 Pegasi: Hot Jupiter? • At that location, expected temperature is VERY high (about 2000K or higher!) • So … Jupiter-like planet, but closer than Mercury  “Hot Jupiter” • How do you make something like that???? 4

  5. Planet Bonanza • Geoff Marcy & Paul Butler quickly confirmed 51 Pegasi • They had lots of archival data from searches for Jupiter-type planets (periods >10 years, so they were still “in progress”) • No one even thought to look for short-period MASSIVE planets (why would they be easier?) • Found many “Hot Jupiters” – most extra-solar planets known today are Hot Jupters 5

  6. ES-Planet Population • As of November 19, 2012, 851 planets are known to orbit other stars in 670 Planetary Systems(!!) • All of this has happened in about 20 years – someone currently finds a new planet every day • These planets are NOT generally like our Solar System objects – WHY? 6

  7. Planets found so far • Note velocity limits • No Earths so far – why? 7

  8. Upsilon Andromedae • First multiple planet system 13

  9. Upsilon AndromedaeA Four-Planet System as of 11/19/12All Jupiter-Size • First multiple planet system 14

  10. HD 209458 • Another Hot Jupiter, a = 0.045 AU 15

  11. HD 209458 • What is a “transit”? 16

  12. HD 209458 • A transit observed • Note: only ~1% dip 17

  13. HD 209458 - Results • Just at the entry moment into transit, for a brief instant, only the upper atmosphere of the planet absorbs any starlight • With a powerful enough spectrograph, we can look for absorption lines at this instant • Result: COMPOSITION of the planet atmosphere • HD 20948b contains – WATER!! 18

  14. Sun and Gliese 581 (Red Dwarf)

  15. Gliese Planetary System

  16. Gliese 581c • Low-mass planet, with mass  5 Mearth • Orbit semi-major axis 0.07 AU • Low-mass star 21

  17. Planets in Habitable Zones • Several planets are currently known in the Habitable Zone around their parent stars • All of these are gas giants  no solid surface • But … gas giants in our Solar System have lots of moons • What happens to Europa if you move it/Jupiter to a distance of 1 AU? 22

  18. Planets in Habitable Zones • What happens to Europa if you move it/Jupiter to a distance of 1 AU? • Really? • Europa mass is closer to our moon’s mass – why no water there? • So … need giant planets in the HZ with giant moons … 23

  19. Planets in Habitable Zones • We don’t see any Earth-mass planets in the HZ • Does this mean they do not exist? 24

  20. Planets in Habitable Zones • Future experiments will use other techniques than Doppler shifts to search for planets • These will have the sensitivity to look for Earth-mass planets in the HZ • Stay tuned! 25

  21. Terrestrial Planet Finder Cancelled, 2011 • Ultra-high-contrast imager satellite • Capable of finding Earth-mass planets in HZ around nearby stars 26

  22. Kepler 22-b, First Earth-Sized Planet in the Habitable Zone of a Sun-Like Star, May 2012

  23. Summary • We have found hundreds of planets around other stars • Overwhelming majority are massive gas giants, many close to their parent star • This is because they are easiest to find with the Doppler technique • Have found: multiple planet systems (20+); planet atmospheres; some low-mass (probably solid) planets • Eccentricity seems more common than circular orbits; problems for life • So far, only a few gas giants in the HZ; no solid planets; maybe moons could host life (??) • Future searches will be sensitive to Earth-mass planets in the HZ 28

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