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Properties of Extrasolar Planets ASTR 241

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Properties of Extrasolar Planets ASTR 241 Properties of Extrasolar Planets ASTR 241 Artist Impression: NASA Properties of Solar System Planets Terrestrial Planets Jovian Planets General Properties small size and mass large size and mass nearly circular orbits high density low density nearly all angular momenta vectors aligned rock & metal H, He, H20, CH4, NH3, … “debris” - astroids, Kuiper belt, Oort Cloud solid surface no solid surface few moons, no rings many moons, no rings close to sun, warm far from sun, warm 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 v ∆λ How Do We Detect Exoplanets? radial = c λ Method #1: Doppler Method Movie credit: ESO Mauna Kea Observatories Photo credit: Richard Wainscoat/Gemini Observatory/AURA/NSF Jupiter’s Doppler Signal Away from us 13 meters per Orbit Period second! Planet Mass Meters per second Toward us What We Found 4.2 days! 0.45 Jupiter masses Meters per second 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 Giant Planet-Metallicity Correlation Fischer and Valenti (2004) Valenti Fischer and 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? 2 π R planet 2 π 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 Kepler: A Mission to Find EarthsTransit Example 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 Kepler-10 Light Curve Batalha et al. (2011) al. et Batalha Transit Depth: 0.00015 Kepler-10b Radius = 1.4 Rearth Period = 0.83 days 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 Planet Density Distribution Weiss & Weiss 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 large size and mass nearly circular orbits high density low density nearly all angular momenta vectors aligned rock & metal H, He, H20, CH4, NH3, … “debris” - astroids, Kuiper belt, Oort Cloud solid surface no solid surface few moons, no rings many moons, no rings close to sun, warm far from sun, warm Properties of Extrasolar Planets Terrestrial Planets Intermediate Planets Jovian Planets they exist! “super-Earths” or “sub-Neptunes” large size and mass small size and mass ubiquitous! low density high density common < 1 AU, maybe > 1AU H, He, H20, CH4, NH3, … rock & metal (probably) low eccentricity orbits no solid surface solid surface (probably) “flat” planetary systems (not-tilted orbits) moons? rings? moons?, rings? all orbital distances common < 1 AU, maybe > 1AU all eccentricities low eccentricities many in tilted orbits prefer metal-rich stars Measurable Properties of Extrasolar Planets Doppler Method Transit Method planet mass ( M sin(i) ) planet size ( radius ) orbital period -> semi-major axis orbital period -> semi-major axis orbital eccentricity orbital eccentricity (in exceptional cases) orbital inclination (in some cases) planet multiplicity planet multiplicity dynamical interactions between planets infer planet temperature infer planet temperature host star properties (Temp, grav., metal content) atmospheric properties Properties of Extrasolar Planets Terrestrial Planets Intermediate Planets Jovian Planets they exist! “super-Earths” or “sub-Neptunes” large size and mass small size and mass ubiquitous! low density high density common < 1 AU, maybe > 1AU H, He, H20, CH4, NH3, … rock & metal (probably) low eccentricity orbits no solid surface solid surface (probably) “flat” planetary systems (not-tilted orbits) moons? rings? moons?, rings? all orbital distances common < 1 AU, maybe > 1AU all eccentricities low eccentricities many in tilted orbits prefer metal-rich stars The End.
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