exoplanets astrobiology workshop june 29, 2006 astrobiology workshop june 29, 2006
TRANSCRIPT
Exoplanets:Exoplanets:Around Solar-Type StarsAround Solar-Type Stars
Exoplanets:Exoplanets:Around Solar-Type StarsAround Solar-Type Stars
Discovery (Discovery (since 1995since 1995) by) by Doppler shifts in spectral lines of stars Transits of stars by planets Microlensing Maybe imaging
Web SitesWeb Sites exoplanet.org exoplanet.eu
Solar System PlanetsSolar System Planets Terrestrial Gas Giant Ice Giant
Jupiter
Earth
Saturn
Neptune
Exoplanets:Exoplanets:Around Solar-Type StarsAround Solar-Type Stars
Exoplanets:Exoplanets:Around Solar-Type StarsAround Solar-Type Stars
CharacteristicsCharacteristics All (or almost all??) are gas or ice giants
• Masses from 7M7MEE up to > 13M > 13MJJ (M (MJJ = 320 M = 320 MEE)) Orbits are mostly unlike the Solar System
• “Hot Neptunes” & “Hot Jupiters” (a <a < 0.4 AU0.4 AU) are common
• Orbits are often very eccentric Earths cannot be detected yet
Numbers (Numbers (>180>180)) Probably at least 10-15%10-15% of nearby Sun-like Stars 18 18 Planetary Systems (stars with 2 or more
planets)
Doppler Shift Doppler Shift due to Stellar Wobbledue to Stellar Wobble
Doppler Shift Doppler Shift due to Stellar Wobbledue to Stellar Wobble
Doppler Shift Doppler Shift due to Stellar Wobbledue to Stellar Wobble
Doppler Shift Doppler Shift due to Stellar Wobbledue to Stellar Wobble
Doppler Shift for a StarDoppler Shift for a StarOrbited by a PlanetOrbited by a Planet
Doppler Shift for a StarDoppler Shift for a StarOrbited by a PlanetOrbited by a Planet
So How Hard Is It?So How Hard Is It?So How Hard Is It?So How Hard Is It?
Difficulty of Doppler SearchesDifficulty of Doppler Searches JupitersJupiters
• C.O.M. of Jupiter-Sun system (5.2 AU5.2 AU orbit radius) is near the Sun’s surface (M(M = 1,000 M = 1,000 MJJ))
• Jupiter orbits the C.O.M. at 13 km/s13 km/s• The Sun’s speed is smaller by the ratio of
Jupiter’s mass to the mass of the Sun (1010-3-3) • The Sun’s wobble due to Jupiter is only 13 m/s13 m/s • The speed of light is 3x103x1088 m/s m/s• For the Doppler effect: // = v/c = v/c• So, we have to detect changes in wavelength
of spectral lines of less thanless than one part in 10one part in 1077 to measure this!
• Massive, close-in gas giants are much easier to detect
So How Hard Is It?So How Hard Is It?So How Hard Is It?So How Hard Is It?
Difficulty of Doppler SearchesDifficulty of Doppler Searches
EarthEarth• The Sun’s wobble due to the Earth is only
about 10 cm/s 10 cm/s !!
Requirements for Any PlanetRequirements for Any Planet• Very stable reference spectrum• Use of all the spectral lines in the spectrum• Problem:Problem: Velocity “noise” from motions in the
star’s atmosphere is typically 1 1 to10 m/s 10 m/s !!
Exoplanets from Doppler Shifts:Exoplanets from Doppler Shifts:General PictureGeneral Picture
Exoplanets from Doppler Shifts:Exoplanets from Doppler Shifts:General PictureGeneral Picture
M V E M J
brown dwarfs
gas giant planets
Extrasolar Planet Discovery Space
Right of the blue line,the orbit period is more
than the time thesesystems have been
observed.
Below the dashedline, the stellar wobbles
are less than 10 m/s.
First Detection of an Exoplanet:First Detection of an Exoplanet:51 Pegasi51 Pegasi
First Detection of an Exoplanet:First Detection of an Exoplanet:51 Pegasi51 Pegasi
First Exo-Planetary System:First Exo-Planetary System:Upsilon AndromedaeUpsilon Andromedae
First Exo-Planetary System:First Exo-Planetary System:Upsilon AndromedaeUpsilon Andromedae
4.2 MJ
1.9MJ0.7MJ
F8V
Eccentric Orbit Example: Eccentric Orbit Example: 16 Cygni b16 Cygni b
Eccentric Orbit Example: Eccentric Orbit Example: 16 Cygni b16 Cygni b
1.7 MJ
G5V
S.S. Analog: S.S. Analog: 47 Ursa Majoris47 Ursa Majoris
S.S. Analog: S.S. Analog: 47 Ursa Majoris47 Ursa Majoris
0.76MJ
2.5MJ
47 Ursa Majoris
55 Cancri: 55 Cancri: A Four Planet SystemA Four Planet System
55 Cancri: 55 Cancri: A Four Planet SystemA Four Planet System
Planet Planet Msini = 4.05 MMsini = 4.05 MJJ
a = 5.9 AU (5,360 days)a = 5.9 AU (5,360 days)Planet Planet Msini = 0.21 MMsini = 0.21 MJJ
a = 0.24 AU (44.3 days)a = 0.24 AU (44.3 days)Planet Planet Msini = 0.84 MMsini = 0.84 MJJ
a = 0.12 AU (14.7 days)a = 0.12 AU (14.7 days)Planet Planet Msini = 0.045 MMsini = 0.045 MJJ (14 M (14 MEE))
a = 0.038 AU (2.81 days)a = 0.038 AU (2.81 days)Star Mass = 0.95 MStar Mass = 0.95 M G8V G8V
Gliese 876 System:Gliese 876 System:Gas Giants in 2:1 ResonanceGas Giants in 2:1 Resonance
Gliese 876 System:Gliese 876 System:Gas Giants in 2:1 ResonanceGas Giants in 2:1 Resonance
Gliese 876 System:Gliese 876 System:6 to 8 Earth Mass Planet6 to 8 Earth Mass Planet
Gliese 876 System:Gliese 876 System:6 to 8 Earth Mass Planet6 to 8 Earth Mass Planet
Gliese 876 System:Gliese 876 System:Three Known PlanetsThree Known PlanetsGliese 876 System:Gliese 876 System:
Three Known PlanetsThree Known Planets
Planet Planet Msini = 1.89 MMsini = 1.89 MJJ
a = 0.21 AU (61.0 days)a = 0.21 AU (61.0 days)Planet Planet Msini = 0.56 MMsini = 0.56 MJJ
a = 0.13 AU (30.1 days)a = 0.13 AU (30.1 days)Planet Planet Msini = 5.9 MMsini = 5.9 MEE
a = 0.021 AU (1.94 days)a = 0.021 AU (1.94 days)Star Mass = 0.32 MStar Mass = 0.32 M M4V M4V
Gliese 876 System:Gliese 876 System:The MovieThe Movie
Gliese 876 System:Gliese 876 System:The MovieThe Movie
Systems Where PlanetsSystems Where PlanetsTransit the StarTransit the Star
Systems Where PlanetsSystems Where PlanetsTransit the StarTransit the Star
Transiting PlanetTransiting PlanetHD209458bHD209458b
Transiting PlanetTransiting PlanetHD209458bHD209458b
Planet Mass = 0.69 Planet Mass = 0.69 0.05 M 0.05 MJJ
Planet Radius = 1.43 Planet Radius = 1.43 0.04 R 0.04 RJJ
Orbit a = 0.045 AUOrbit a = 0.045 AUOrbit Period = 3.52 daysOrbit Period = 3.52 daysStar Mass = 1.05 MStar Mass = 1.05 M (F8V) (F8V)
Transiting PlanetTransiting PlanetHD209458bHD209458b
Transiting PlanetTransiting PlanetHD209458bHD209458b
Transiting Planet HD209458b:Transiting Planet HD209458b:Absorption Line of SodiumAbsorption Line of Sodium
Transiting Planet HD209458b:Transiting Planet HD209458b:Absorption Line of SodiumAbsorption Line of Sodium
Transiting Planet HD149026b: Transiting Planet HD149026b: A Massive Heavy CoreA Massive Heavy Core
Transiting Planet HD149026b: Transiting Planet HD149026b: A Massive Heavy CoreA Massive Heavy Core
Transiting Planet HD149026b: Transiting Planet HD149026b: A Massive Heavy CoreA Massive Heavy Core
Transiting Planet HD149026b: Transiting Planet HD149026b: A Massive Heavy CoreA Massive Heavy Core
Planet Mass = 0.36 MPlanet Mass = 0.36 MJJ
Planet Radius = 0.72 Planet Radius = 0.72 0.025 R 0.025 RJJ
Orbit a = 0.042 AUOrbit a = 0.042 AUOrbit Period = 2.88 daysOrbit Period = 2.88 daysStar Mass = 1.31 MStar Mass = 1.31 M G0IV G0IV
Doppler-Shift Exoplanets:Doppler-Shift Exoplanets:Masses, Eccentricities, & OrbitsMasses, Eccentricities, & Orbits
Doppler-Shift Exoplanets:Doppler-Shift Exoplanets:Masses, Eccentricities, & OrbitsMasses, Eccentricities, & Orbits
BrownDwarf Desert
Doppler-Shift Exoplanets:Doppler-Shift Exoplanets:Masses & OrbitsMasses & Orbits
Doppler-Shift Exoplanets:Doppler-Shift Exoplanets:Masses & OrbitsMasses & Orbits
NEPTUNESJUPITERS
ALL
Highest Mass
Average Mass 30 m/s
10 m/s
Doppler-Shift Exoplanets:Doppler-Shift Exoplanets:Eccentricities & Orbit PeriodsEccentricities & Orbit Periods
Doppler-Shift Exoplanets:Doppler-Shift Exoplanets:Eccentricities & Orbit PeriodsEccentricities & Orbit Periods
Doppler-Shift Exoplanets:Doppler-Shift Exoplanets:Metallicity of the Host StarMetallicity of the Host StarDoppler-Shift Exoplanets:Doppler-Shift Exoplanets:
Metallicity of the Host StarMetallicity of the Host Star
Some statistics
[Fe/H] is the log10 of Fe/H in thestar divided by the Sun’s value.
Transiting Exoplanets:Transiting Exoplanets:Are They Like Jupiter and Saturn?Are They Like Jupiter and Saturn?
Transiting Exoplanets:Transiting Exoplanets:Are They Like Jupiter and Saturn?Are They Like Jupiter and Saturn?
J
S
1.3 g/cc
0.3 g/cc
Issues and Concerns:Issues and Concerns:Planet FormationPlanet Formation
Issues and Concerns:Issues and Concerns:Planet FormationPlanet Formation
Planet FormationPlanet Formation Gas Giant Formation TheoriesGas 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:Hybrid: Core Accretion sped up by Disk Instability?
EvidenceEvidence• Metallicity correlation may favor Core Accretion
Issues and Concerns:Issues and Concerns:Planet FormationPlanet Formation
Issues and Concerns:Issues and Concerns:Planet FormationPlanet Formation
Hot Neptunes & Jupiters?Hot Neptunes & Jupiters? Formation in Place Formation in Place
• Probably not possible Planet “Migration”Planet “Migration”
• Planets can drift inward due to planet-disk interaction
Eccentricities?Eccentricities? How Are They Attained?How Are They Attained?
• Multi-body interactions• Perturbations by nearby stars• Planet-disk interactions• Migration into orbital resonances
OverallOverall Incredible Diversity of Planetary Systems!Incredible Diversity of Planetary Systems!
Formation of the Solar System:Formation of the Solar System:The “Solar Nebula” TheoryThe “Solar Nebula” Theory
Formation of the Solar System:Formation of the Solar System:The “Solar Nebula” TheoryThe “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
Gas Giant Planet Formation:Gas Giant Planet Formation:The Two TheoriesThe Two Theories
Gas Giant Planet Formation:Gas Giant Planet Formation:The Two TheoriesThe Two Theories
Core Accretion Disk Instability
few x106 yrs 102 - 103 yrs
Issues and Concerns:Issues and Concerns:LifeLife
Issues and Concerns:Issues and Concerns:LifeLife
Why Are Hot Jupiters Bad?Why Are Hot Jupiters Bad? OriginOrigin
• Probably exist due to inward “migration” during planet formation
EffectsEffects• 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?Why Are Eccentric Gas Giants Bad? EffectsEffects
• Tend to disrupt terrestrial planet formation• Tend to destabilize terrestrial planet orbits and/or force
the orbits to be eccentric, producing extreme seasons
Issues and Concerns:Issues and Concerns:LifeLife
Issues and Concerns:Issues and Concerns:LifeLife
Hope?Hope? There ARE Solar System Analogs! 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!Incredible Diversity of Environments! And…And…