Exoplanets Astrobiology Workshop June 29, 2006 Astrobiology Workshop June 29, 2006

ExoplanetsExoplanets

Astrobiology WorkshopJune 29, 2006

Astrobiology WorkshopJune 29, 2006

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



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 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

Latest VersionLatest VersionLatest VersionLatest Version

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


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 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

Transit SurveysTransit SurveysTransit SurveysTransit Surveys

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

Image of a Planet?Image of a Planet?Image of a Planet?Image of a Planet?

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


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



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


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



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…

Maybe Close-In Gas Giants Have Maybe Close-In Gas Giants Have Earth-Like MoonsEarth-Like Moons

Maybe Close-In Gas Giants Have Maybe Close-In Gas Giants Have Earth-Like MoonsEarth-Like Moons

Documents

Exoplanets Astrobiology Workshop June 29, 2006 Astrobiology Workshop June 29, 2006