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Exoplanets

Exoplanets. Astrobiology Workshop June 29, 2006. Exoplanets: Around Solar-Type Stars. Discovery ( since 1995 ) by Doppler shifts in spectral lines of stars Transits of stars by planets Microlensing Maybe imaging Web Sites exoplanet.org exoplanet.eu Solar System Planets Terrestrial

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Exoplanets

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  1. Exoplanets Astrobiology Workshop June 29, 2006

  2. Exoplanets:Around Solar-Type Stars • Discovery (since 1995) by • Doppler shifts in spectral lines of stars • Transits of stars by planets • Microlensing • Maybe imaging • Web Sites • exoplanet.org • exoplanet.eu • Solar System Planets • Terrestrial • Gas Giant • Ice Giant Earth Neptune Jupiter Saturn

  3. Exoplanets:Around Solar-Type Stars • Characteristics • All (or almost all?) are gas or ice giants • Masses from7MEup to > 13MJ (MJ = 320 ME) • Orbits are mostly unlike the Solar System • “Hot Neptunes” & “Hot Jupiters” (a <0.4 AU) are common • Orbits are often very eccentric • Earths cannot be detected yet • Numbers (>180) • Probably at least 10-15% of nearby Sun-like Stars • 18 Planetary Systems (stars with 2 or more planets)

  4. Doppler Shift due to Stellar Wobble

  5. Doppler Shift due to Stellar Wobble

  6. Doppler Shift for a StarOrbited by a Planet

  7. So How Hard Is It? • Difficulty of Doppler Searches • Jupiters • C.O.M. of Jupiter-Sun system (5.2 AU orbit radius) is near the Sun’s surface (M = 1,000 MJ) • Jupiter orbits the C.O.M. at 13 km/s • The Sun’s speed is smaller by the ratio of Jupiter’s mass to the mass of the Sun (10-3) • The Sun’s wobble due to Jupiter is only 13 m/s • The speed of light is 3x108 m/s • For the Doppler effect: / = v/c • So, we have to detect changes in wavelength of spectral lines of less thanone part in 107 to measure this! • Massive, close-in gas giants are much easier to detect

  8. So How Hard Is It? • Difficulty of Doppler Searches • Earth • The Sun’s wobble due to the Earth is only about 10 cm/s ! • Requirements for Any Planet • Very stable reference spectrum • Use of all the spectral lines in the spectrum • Problem: Velocity “noise” from motions in the star’s atmosphere is typically 1 to10 m/s !

  9. Exoplanets from Doppler Shifts:General Picture M M V E J

  10. Latest Version

  11. Extrasolar Planet Discovery Space Right of the blue line, the orbit period is more than the time these systems have been observed. brown dwarfs gas giant planets Below the dashed line, the stellar wobbles are less than 10 m/s.

  12. First Detection of an Exoplanet:51 Pegasi

  13. First Exo-Planetary System:Upsilon Andromedae F8V 4.2 MJ 1.9MJ 0.7MJ

  14. Eccentric Orbit Example: 16 Cygni b 1.7 MJ G5V

  15. S.S. Analog: 47 Ursa Majoris 47 Ursa Majoris 2.5MJ 0.76MJ

  16. 55 Cancri: A Four Planet System Planet Msini = 4.05 MJ a = 5.9 AU (5,360 days) Planet Msini = 0.21 MJ a = 0.24 AU (44.3 days) Planet Msini = 0.84 MJ a = 0.12 AU (14.7 days) Planet Msini = 0.045 MJ (14 ME) a = 0.038 AU (2.81 days) Star Mass = 0.95 M G8V

  17. Gliese 876 System:Gas Giants in 2:1 Resonance

  18. Gliese 876 System:6 to 8 Earth Mass Planet

  19. Gliese 876 System:Three Known Planets Planet Msini = 1.89 MJ a = 0.21 AU (61.0 days) Planet Msini = 0.56 MJ a = 0.13 AU (30.1 days) Planet Msini = 5.9 ME a = 0.021 AU (1.94 days) Star Mass = 0.32 M M4V

  20. Gliese 876 System:The Movie

  21. Systems Where PlanetsTransit the Star

  22. Transiting PlanetHD209458b Planet Mass = 0.69  0.05 MJ Planet Radius = 1.43  0.04 RJ Orbit a = 0.045 AU Orbit Period = 3.52 days Star Mass = 1.05 M (F8V)

  23. Transiting PlanetHD209458b

  24. Transiting Planet HD209458b:Absorption Line of Sodium

  25. Transit Surveys

  26. Transiting Planet HD149026b: A Massive Heavy Core

  27. Transiting Planet HD149026b: A Massive Heavy Core Planet Mass = 0.36 MJ Planet Radius = 0.72  0.025 RJ Orbit a = 0.042 AU Orbit Period = 2.88 days Star Mass = 1.31 M G0IV

  28. Image of a Planet?

  29. Doppler-Shift Exoplanets:Masses, Eccentricities, & Orbits Brown Dwarf Desert

  30. Highest Mass ALL Average Mass 30 m/s 10 m/s NEPTUNES JUPITERS Doppler-Shift Exoplanets:Masses & Orbits

  31. Doppler-Shift Exoplanets:Eccentricities & Orbit Periods

  32. Doppler-Shift Exoplanets:Metallicity of the Host Star Some statistics [Fe/H] is the log10 of Fe/H in the star divided by the Sun’s value.

  33. 1.3 g/cc 0.3 g/cc J S Transiting Exoplanets:Are They Like Jupiter and Saturn?

  34. Issues and Concerns:Planet Formation • Planet Formation • Gas Giant Formation Theories • Solid Core Accretion followed by gas capture • Pro: Mechanism that can work • Con: Slow, expect formation at > few AU, may not be able to make super-Jupiters • Disk Instability due to self-gravity of the protoplanetary disk • Pro: Fast formation • Con: Real protoplanetary disks may not cool fast enough to fragment, may be hard to explain large solid cores • Hybrid:Core Accretion sped up by Disk Instability? • Evidence • Metallicity correlation may favor Core Accretion

  35. Issues and Concerns:Planet Formation • Hot Neptunes & Jupiters? • Formation in Place • Probably not possible • Planet “Migration” • Planets can drift inward due to planet-disk interaction • Eccentricities? • How Are They Attained? • Multi-body interactions • Perturbations by nearby stars • Planet-disk interactions • Migration into orbital resonances • Overall • Incredible Diversity of Planetary Systems!

  36. Formation of the Solar System:The “Solar Nebula” Theory Dense, Cold, Rotating Interstellar Cloud Collapses and Flattens Sun Forms with “Solar Nebula” (Protoplanetary Disk) Solid Planetesimals and Gas Giant Planets Form, Then Gas Dissipates Terrestrial Planets Form by Accretion of Planetesimals 105 yrs 106-107 yrs 107-3x107 yrs

  37. Core AccretionDisk Instability few x106 yrs 102 - 103 yrs Gas Giant Planet Formation:The Two Theories

  38. Issues and Concerns:Life • Why Are Hot Jupiters Bad? • Origin • Probably exist due to inward “migration” during planet formation • Effects • Sweep terrestrial planet material into the star as they migrate • Gas Giants near or inside the habitable zone make stable orbits for terrestrial planets difficult or impossible • Why Are Eccentric Gas Giants Bad? • Effects • Tend to disrupt terrestrial planet formation • Tend to destabilize terrestrial planet orbits and/or force the orbits to be eccentric, producing extreme seasons

  39. Issues and Concerns:Life • Hope? • There ARE Solar System Analogs! • Gas giants at > few AU in nearly circular orbits • Over the next decade, more are likely to be found • Incredible Diversity of Environments! • And…

  40. Maybe Close-In Gas Giants Have Earth-Like Moons

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