1. Extra-Solar Planet Populations Stephen Eikenberry 4 November 2010 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!!! 2 How? Doppler shift of spectral lines

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 M JUP  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 on 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 this morning, 228 861 planets are now known to orbit other stars (!!) All of this has happened in about 15 years – someone currently finds a new planet every couple of days or less These planets are NOT generally like our Solar System objects – WHY? 6

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10. Upsilon Andromedae First multiple planet system 10

11. Upsilon Andromedae First multiple planet system 11

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13. HD 209458 Another Hot Jupiter 13

14. HD 209458 What is a “transit”? 14

15. HD 209458 A transit observed Note: only ~1% dip 15

16. 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!! 16

17. Gliese 581c Low-mass planet, with mass  5 M earth Orbit semi-major axis 0.07 AU Low-mass star 17

18. Gliese 581c Just inside Habitable Zone Gliese 581d just outside HZ 18

19. Eccentricity 19

20. 20 Circumbinary Planets

21. 21 Transiting Planets in the HZ Image Credits: NASABorucki et al. 2012Orosz et al. 2012

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23. Planets in Habitable Zones Many planets are currently known in the Habitable Zone around their parent stars Most 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? 23

24. 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 … 24

25. 25 Our Solar System is Not Typical Sun is an unusually massive star Our solar system has no planets with orbital periods less than Mercury Our inner solar system does not have a super-Earth-size to Neptune-size planet Most planetary systems don’t have a Jupiter analog → Planet formation theories should typically produce planetary systems unlike our own Borucki+ 2011; Batalha+ 2012; Howard+ 2012; Fressin+ 2013; Burke+ in prep

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

27. 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; but Kepler mission (transits) is changing that 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; first possibly-solid planets; maybe moons could host life (??) Future searches will be sensitive to Earth-mass planets in the HZ 27

28. Exoplanet Zoo: Examples We have found hundreds of planets around other stars 28

29. Exoplanet Zoo: Examples Multiple-planet systems 29

30. Exoplanet Zoo: Examples OGLE-2005-BLG-390Lb – 5.5 Earth-mass, far from star (T=-360 ˚F) COROT-7b: 4.8 Earth-mass, density = Earth-density (!); close to star (T ~1300K) Gliese 581g: 3-4 Earth-mass; T ~- 25 ˚F to +160 ˚F; in the Habitable Zone (!), but tidally locked 30