Download Properties of Extrasolar Planets

Properties of Extrasolar Planets
ASTR 241
Artist Impression: NASA
Properties of Solar System Planets
Terrestrial Planets
Jovian Planets
General Properties
small size and mass
high density
rock & metal
solid surface
few moons, no rings
close to sun, warm
large size and mass
low density
H, He, H20, CH4, NH3, …
no solid surface
many moons, no rings
far from sun, warm
nearly circular orbits
nearly all angular momenta vectors aligned
“debris” - astroids, Kuiper belt, Oort Cloud
Confirmed Planets - 2013
Transits
RV Microlensing
Imaging
Solar System
Pulsar Timing
Data: exoplanets.org
Exoplanet Detection Methods
(planet = extrasolar planet = exoplanet)
Doppler Method
Transit Method
How Do We Detect Exoplanets?
Method #1: Doppler Method
vradial
=
c
Movie credit: ESO
Mauna Kea Observatories
Photo credit: Richard Wainscoat/Gemini Observatory/AURA/NSF
Jupiter’s Doppler Signal
Away from us
Meters per second
Orbit Period
Toward us
13 meters per second!
Planet Mass
What We Found
Meters per second
4.2 days! 0.45 Jupiter masses
51 Pegasi
Hot Jupiter
1% of Sun-­‐like stars have one
Image: NASA
Determination of Orbital Distance !
from Star to Planet
Period = 4.2 days!
!
Kepler’s 3rd Law: P2 = a3!
!
Units: P in years, a in AU!
!
Solve for a:!
a = 0.05 AU!
!
Proximity: Temp = 1800 C
Determination of Planet’s Mass
Conservation of Momentum: !
momentum of star = momentum of planet!
!
MSTAR VSTAR = Mplanet Vplanet
Solve for Mass of planet:!
Mplanet = MSTAR VSTAR / Vplanet
MSTAR : Star Masses are known !
(most are Sun-like)
VSTAR from Doppler shift (semi-amplitude): !
55 m/s
What is Vplanet ?
Vplanet = 2 π a / P!
You know “a” from Kepler’s 3rd Law: P2 = a3
Can Determine Mplanet
Mercury’s Orbit orbital distance = 0.39 AU!
Temp = 800 degrees
51 Peg b’s Orbit orbital distance = 0.05 AU!
Temp = 1,800 degrees
Semi-major Axes (Orbital Distances)
for Jovian Planets
~20% of Sun-like stars
have a giant planet
orbiting within 10 AU
Orbital Eccentricities of Jovian Planets
e = 0.01
e = 0.06
e = 0.05
e = 0.02
Orbital Eccentricity
Fischer and Valenti (2004)
Giant Planet-Metallicity Correlation
Giant Planets are more common around stars rich in metals!
This is a clue to planet formation!
Systems of Planets
Four-piter
Two-piter
Dinky
Doppler Method of Planet Detection
Measurable quantities
planet mass ( M sin(i) )
orbital period (P) → semi-major axis (a)
orbital eccentricity (e)
orbital inclination (in some cases)
planet multiplicity (# of planets per star)
infer planet temperature
host star properties (temperature, gravity, metal content)
How Do We Detect Exoplanets? Method #2:
Transit Method
Question for Students:
How big is the planet?
π R2planet
π
2
R
star
Transit Method of Planet Detection
Measurable quantities
planet size ( radius )
orbital period → semi-major axis
orbital eccentricity (in exceptional cases)
planet multiplicity
dynamical interactions between planets
infer planet temperature
atmospheric properties
Transit
Example
Kepler: A Mission to Find Earths
Image: NASA
Kepler-10 Light Curve
24
Kepler-10 Light Curve
Period = 45.29 days
25
Kepler-10 Light Curve
Period = 45.29 days
26
Period = 45.29 days
Kepler-10 Light Curve
Period = 45.29 days
Kepler-10 Light Curve
Period = 0.84 days
Transit Depth:
0.00015
Kepler-10b
Radius = 1.4 Rearth
Period = 0.83 days
Batalha et al. (2011)
Kepler-­‐10 Light Curve
Planet Size and Mass Distributions
Small planets are ubiquitous!
Most stars have close-in “super-Earth” Planets!
Why doesn’t the Solar System
have a super-Earth?
Known Planets - Masses and Radii
Howard et al. 2013 (Nature)
Possible Compositions for super-Earth Planets
Different admixtures of H/He, water, rock, iron
Weiss &
Planet Density Distribution
Planets Larger than ~1.5X Earth-size are low density.
Smaller planets are high density.
Kepler-78b - A Planet the Size and Mass of Earth
Howard et al. 2013 (Nature)
Multiple Planets Orbiting the Same Star are Common
Our Solar System
Video: Dan Fabrycky
What about Earth-like Planets
Image: NASA
Kepler-186
Credit: NASA
Image: NASA
Erik Petigura
Exoplanet Atmospheres
Planets have slightly different sizes
when measured at different wavelengths
because of their atmospheres
Properties of Solar System Planets
Terrestrial Planets
Jovian Planets
General Properties
small size and mass
high density
rock & metal
solid surface
few moons, no rings
close to sun, warm
large size and mass
low density
H, He, H20, CH4, NH3, …
no solid surface
many moons, no rings
far from sun, warm
nearly circular orbits
nearly all angular momenta vectors aligned
“debris” - astroids, Kuiper belt, Oort Cloud
Properties of Extrasolar Planets
Terrestrial Planets
Intermediate Planets
Jovian Planets
they exist!
small size and mass
high density
rock & metal (probably)
solid surface (probably)
moons?, rings?
common < 1 AU, maybe > 1AU
low eccentricities
“super-Earths” or “sub-Neptunes”
ubiquitous!
common < 1 AU, maybe > 1AU
low eccentricity orbits
“flat” planetary systems (not-tilted orbits)
large size and mass
low density
H, He, H20, CH4, NH3, …
no solid surface
moons? rings?
all orbital distances
all eccentricities
many in tilted orbits
prefer metal-rich stars
Measurable Properties of Extrasolar Planets
Doppler Method
Transit Method
planet mass ( M sin(i) )
orbital period -> semi-major axis
orbital eccentricity
orbital inclination (in some cases)
planet multiplicity
infer planet temperature
host star properties (Temp, grav., metal content)
planet size ( radius )
orbital period -> semi-major axis
orbital eccentricity (in exceptional cases)
planet multiplicity
dynamical interactions between planets
infer planet temperature
atmospheric properties
Properties of Extrasolar Planets
Terrestrial Planets
Intermediate Planets
Jovian Planets
they exist!
small size and mass
high density
rock & metal (probably)
solid surface (probably)
moons?, rings?
common < 1 AU, maybe > 1AU
low eccentricities
“super-Earths” or “sub-Neptunes”
ubiquitous!
common < 1 AU, maybe > 1AU
low eccentricity orbits
“flat” planetary systems (not-tilted orbits)
large size and mass
low density
H, He, H20, CH4, NH3, …
no solid surface
moons? rings?
all orbital distances
all eccentricities
many in tilted orbits
prefer metal-rich stars
The End