Dr. Matt Burleigh 3677: Life in the Universe DEPARTMENT OF PHYSICS AND ASTRONOMY 3677 Life in the Universe Extra-solar planets: Revision Dr. Matt Burleigh

Dr. Matt Burleigh 3677: Life in the Universe Course outline Lecture 1Lecture 1 –Definition of a planet –A little history –Pulsar planets –Doppler “wobble” (radial velocity) technique Lecture 2Lecture 2 –Transiting planets –Transit search projects –Detecting the atmospheres of transiting planets

Dr. Matt Burleigh 3677: Life in the Universe Course outline Lecture 3Lecture 3 –Microlensing –Direct Imaging –Planets around evolved stars Lecture 4Lecture 4 –Statistics: mass and orbital distributions, incidence of solar systems, etc. –Hot Jupiters –Super-Earths –Planetary formation –The host stars

Dr. Matt Burleigh 3677: Life in the Universe Course outline Lecture 5Lecture 5 –The quest for an Earth-like planet –Results from the Kepler mission –Habitable zones –Biomarkers –Future telescopes and space missions

Dr. Matt Burleigh 3677: Life in the UniverseKepler Searching for Earths by transit methodSearching for Earths by transit method Launched 2009 by NASALaunched 2009 by NASA 0.95m schmidt telescope, FOV ~ 105 square deg.0.95m schmidt telescope, FOV ~ 105 square deg. 150,000 MS stars, with V=10 - >14 mag150,000 MS stars, with V=10 - >14 mag Aim: find an Earth around a Sun-like star in a one year orbitAim: find an Earth around a Sun-like star in a one year orbit Need three transitsNeed three transits So mission lasts at least three years…So mission lasts at least three years… Jupiter Earth

Dr. Matt Burleigh 3677: Life in the Universe Kepler results Petigura et al. 2013: 11±4% of sun-like stars have an Earth- sized planet receiving 1 to 4 times the stellar intensity that Earth receives define “Earth-sized” as 1-2R Earth 5.7% (+1.7% - 2.2%) of Sun-like stars have an Earth-sized planet with orbital periods between 200 & 400 days 22% of Sun-like stars have Earth-sized planets orbiting within their habitable zones (generous definition of HZ includes Venus & Mars!) If the Kepler field of view is taken to be representative of the local neighbourhood then this suggests that the nearest such planet could be within 12 light years

Dr. Matt Burleigh 3677: Life in the Universe Kepler’s limitations Kepler observes probable transit eventsKepler observes probable transit events “Validates” these“Validates” these –with 3 transits –tries to rule out background binaries/triple star systems –Statistical likelihood planet is “real”

Dr. Matt Burleigh 3677: Life in the Universe Planet Hunting: The Radial Velocity Technique (“Doppler Wobble”) (“Doppler Wobble”) (“Doppler Wobble”) Star + planet orbit common centre of gravity Star + planet orbit common centre of gravity As star moves towards observer, wavelength of light shortens (blue- shifted) As star moves towards observer, wavelength of light shortens (blue- shifted) Light red-shifted as star moves away Light red-shifted as star moves away 873 planets detected by Doppler Wobble inc. 142 multiple systems

Dr. Matt Burleigh 3677: Life in the Universe Measuring Stellar Doppler shifts Method:Method: –Observe star’s spectrum through a cell of iodine gas –Iodine superimposes many lines on star’s spectrum –Measure wavelength (or velocity) of star’s lines relative to the iodine Measure:Measure: –  e = (   e ) / e = v r / c   observed wavelength, e =emitted wavelength

Dr. Matt Burleigh 3677: Life in the Universe M * from spectral type

Dr. Matt Burleigh 3677: Life in the Universe Doppler Wobble Method Since measure K (= v * sin i), not v * directly, only know mass in terms of the orbital inclination iSince measure K (= v * sin i), not v * directly, only know mass in terms of the orbital inclination i Therefore only know the planet’s minimum mass, M sin iTherefore only know the planet’s minimum mass, M sin i –If i=90 o (eclipsing or transiting) then know mass exactly i=90 0 Orbital plane i0i0i0i0

Dr. Matt Burleigh 3677: Life in the Universe Transits Probability of transit (for random orbit)Probability of transit (for random orbit) –For Earth (a=1AU), P transit =0.5% –But for close, “hot” Jupiters, P transit =10% –Of course, relative probability of detecting Earths is lower since would have to observe continuously for up to 1 year (See Kepler mission)(See Kepler mission)

Dr. Matt Burleigh 3677: Life in the Universe Transits For an edge-on orbit, transit duration is given by:For an edge-on orbit, transit duration is given by: Where P=period, a=semi-major axis of orbitWhere P=period, a=semi-major axis of orbit Example: HD209458bExample: HD209458b –P= days = s –R * =1.15R Sun = 1.15x6.955x10 8 m –a= AU=7.1x10 9 m –Δt=10920s=3.03hours –Note for Earth (a=1AU) Δt=46668s=12.96hours