2003 UB313: The 10th Planet? Extra-Solar or Exoplanets • Planets around stars other than the Sun • Difficult to observe • Hundreds discovered (> 2000 so far) Circa 2013, Courtesy Kepler: Billions!! • Jupiter to Earth sizes • Surprise: Some stars with Jupiter mass planets within 1 AU (revised theory of planet formation ?) • Goldilocks Zone: Habitable Distance out to where water is liquid Extra-solar planets around distant stars First image of an exoplanet Transiting Hot Saturn with a large dense core Astronomers have found a weird new creature: a planet whose core holds 65 Earths' worth of heavy rocky stuff. Saturn-mass planet transiting across its star Discovering Planets with Life Sunlight is reflected off the Earth, hits the Moon and bounces back to Earth Earthshine is seen in the faint glow our world gives to dark areas of the Moon The light carries information about Earth's atmosphere and surface properties Scientists see details in the light that betray different gases, even vegetation The knowledge can be applied to the search for distant worlds Detect the presence of atoms/molecules that make up vegetation or life 7.5 Earth-mass planet Found: 3 'Neptunes' and a 'hot Jupiter' 600 LY’s from the Earth, the planetary system is in the habitable zone with conditions enabling liquid water to exist HD 188753 b - A planet in a triple star system 5.9 Earth mass planet in Gliese 876 system Introduction ● ● ● ● ● What are exoplanets? How do we find them? What can our detection methods tell us about them? How do planets form? What have we found? Exoplanet Detection Methods ● Transits – ● Radial Velocity (RV) – ● Observe Doppler shift as star “wobbles” over planetary orbit Direct Imaging – ● Observe light dip as planet moves in front of a star Exactly what it says on the can Microlensing – Use gravitational lensing to find planets Transits ● ● ● ● Observe light dip as planet moves in front of the star Find orbital period, radius of the planet compared to the star, stellar density Preferentially finds large, short-period planets Most prolific detection method today (Kepler mission) Transit Video http://www.eso.org/public/videos/eso50lighti ntensityexo/ Transit light curve Radial Velocity ● ● ● ● Uses the Doppler Effect Observe shift in spectral lines as planet tugs star to and fro Preferentially finds massive, short-period planets Find mass of planet compared to the star, orbital period directly RV video http://www.eso.org/public/videos/eso1035g/ RV curve Direct Imaging ● ● ● ● ● Just take a picture of the planet VERY hard to do; planets are faint and stars are bright To do from the ground, need large telescopes and adaptive optics Preferentially find large, young planets far from their star Very few planets detected this way HR 8799 Microlensing ● ● ● ● ● Use gravitational lensing to find planets Star with a planet passes in front of a more distant star Lensing star magnifies the light of the background star; planet can affect this Preferentially find massive planets in orbits similar to the Earth's against dense stellar background (galactic bulge) Done at OSU! Microlensing Video http://www.eso.org/public/videos/eso50micr olensingexo/ Microlensing Diagram Planet Detection Demographics Planet Demographics Figure Labels Red = detected by transits Blue = RVs/Doppler shifts Green = microlensing Tan = direct imaging History of Exoplanets ● ● ● RV method the first to be used Followed by transits and microlensing Direct Imaging only possible recently First Exoplanet Discovered! ● ● ● ● ● 1995 51 Pegasi b, using RV method 0.5 Jupiter-mass planet on ~4 day orbit (?!) Enormous surprise; discovering scientists proposed it wasn't a planet at all! Opened the floodgates First Transiting Exoplanet Discovered! ● ● ● ● ● 2000 HD 209458 b Also hot Jupiter; 0.7 Jupiter masses, 3.5 day orbit Discovered “right on time” First planet discovered solely by transits in 2003 Kepler Mission ● ● ● ● ● Designed to stare at one patch of sky for years on end Looking for transiting planets Capable of extremely high photometric precision First Earth-sized planets discovered! Thousands of planet candidates detected Kepler Field All Kepler Planets Discovered So Far Aside: Planetary Formation ● ● Two dominant models: core accretion and gravitational instability Core accretion – – – ● Little rocks collide and stick together to form bigger rocks Eventually gravity holds big rocks together and attracts them to each other Build up each planet bit by bit Gravitational Instability – Have very massive, cold disk which becomes So what have we found? ● ● ● ● ● ● Planets are everywhere! Other solar systems are NOT like our own! Hot Jupiters (how did those get there?) Super-Earths Hot Neptunes Many more questions... Hot Jupiters ● ● Gas giant planets very close to their parent star Problem because of planetary formation models – – Think that giants need to form beyond “snow line” Migration? How? ● ● Three ideas: planet-planet interactions, disks, binary star interactions Rare: Only about 1% of Sun-like stars Hot Jupiter Weather Earth-sized Planets ● ● Very common, even around metal-poor and less massive stars Exist in wide range of environments – – 17% of stars have Earth-sized planet inside the orbit of Mercury ~20% of stars have Earth-sized planets within the habitable zone Where Do We Go From Here? ● ● ● ● Planetary atmospheres Better planetary formation models Protoplanetary disk evolution Life?