Summerschool on Geophysics of Terrestrial Planets July 21, 2014, Alpbach, Austria Geophysics of Extrasolar Planets Hauke Hussmann, (including material from F. Sohl, F. Wagner, H. Rauer) DLR Institute of Planetary Research Berlin, Germany Overview Module Introduction to Extrasolar Systems Exoplanet Hunting Geophysics of Extrasolar Planets Specific Applications Major Open Questions Future Exploration Overview Module Introduction to Extrasolar Systems Exoplanet Hunting Geophysics of Extrasolar Planets Specific Applications Major Open Questions Future Exploration Discoveries Module Status (as of July 2014): 1810 planets 1125 planetary systems 466 multiple planet systems First important facts: (1) A large variety of planets, planetary orbits, and host stars have been detected. (2) We can set the solar system into context to many other planetary systems. However: We have to consider a substantial observational bias. Some regions of the possible parameter space for planetary detections are not yet accessible. Detection Methods I: Radial Velocity Method Module Left: The Doppler shift can be used to determine the star’s motion around the barycenter. Because of the unknown orientation of the system the mass is constrained by M sin i by the RV method, with i being the orbital inclination of the planet. Right: Variations of the radial velocity of TW Hydrae as observed in early 2007. The data can best be described as an oscillation with a period of 3.6 days, caused by a giant planet orbiting around the star. Picture: Max Planck Institute for Astronomy Detection Methods II: Planetary Transits ModuleLight-curves are measured during revolution of the planet. The planet’s transit causes a drop in the stellar light curve. A secondary drop, especially in the thermal infrared can be observed by the occultation of the star (secondary eclipse). Below: Examples of detections by the Kepler Mission Detection Methods III: Micro-Lensing Module Example of a micro-lensing detection: A micro-lensing light curve In this case, only a very low mass planetary produced by the relative movement companion to the lensing body (an M-dwarf) could of a star-planet system with respect explain the observations. to a background source. The planet has a mass of 5.5 times the mass of the Image Credit: Dave Bennett (Notre Earth Dame) The companion was named OGLE-2005-BLG-390Lb (L=lens, b=lens component) It is a "cool" planet (estimated surface temperature - 220 degrees Celsius) at a distance of about 2.6 AU. Detection Methods IV: Direct Imaging Module HR8799 direct imaging planet detections Credit: Marois et al (2010) - A technique that is sensitive to massive planets at large orbital distances— more distant than Neptune. - It provides a completely new and complementary set of parameters such as luminosity, as well as detailed spectroscopic information. It provides clues to the planets’ atmospheric chemistry, perhaps even to non-equilibrium chemistry associated with these objects. - The method characterizes planetary systems, especially at young ages where the radial velocity methods are hampered by the intrinsic stellar “jitter” of the stars. - Important data for various planet formation models. - Major obstacle is the overwhelming brightness of the host star. Detection Methods V: Timing Module Pulsar planets Pulsars (supernova remnants of massive stars) can spin with a rotation period of just a couple of milliseconds (so-called millisecond pulsars). The accuracy of the pulsed beams coming from these stars can rival that of atomic clocks on the Earth. Because the pulsars are so steady in their timing, periodic deviations could signify the presence of an unseen body in orbit. The very first planets ever discovered were found in orbit around a pulsar. In 1992, astronomer using the Arecibo Radio Telescope in Puerto Rico discovered just such a periodic variation in the timing of the pulsar PSR B1257+12, a millisecond pulsar 980 light-years away. Analysis of the variations indicated that not one, but two planets were in orbit around the pulsar! Further study eventually revealed a third world in this exotic system. Detection Methods Compared Module Timing: Pulsar Planets only, very exotic systems, unclear how planets form or survive, Sensitive to very low masses Micro-lensing: Very sensitive to low-mass planets (Mars-sized objects); opportunity for detection only once because of special geometrical condition; no confirmation or follow- up observations possible; distant and low-mass planets can be detected. Direct Imaging: Only distant planets can be detected; direct measurements of luminosity and spectroscopic features. Transit: Only planets in line-of sight with the star (specific viewing angles); radius can be determined from measurement Doppler velocity: Mass (i.e.M sin i) can be constrained; works best for close massive planets (strong observational bias); eccentricity can be measured directly Best characterization (mass and radius) by combined transit and radial velocity measurements. => Importance of follow-up measurements for transit detections. Detection Methods: Statistics Module planets systems mult. plan. sys. Radial Velocity 574 430 102 Planetary Transits: 1140 620 352 Micro-lensing 30 28 2 Imaging 50 46 2 Timing 15 12 2 Status: as of July 2014; Source: http://exoplanet.eu/catalog/ Green: Transits Blue: Radial Velocity Red: Imaging Brown: Micro-lensing Yellow: Timing Orbits of Extrasolar Systems Module Many massive planets have orbits very close to their host stars. Observational bias: detection methods favor the detection of massive planets orbiting close to their host stars. Orbits of Extrasolar Systems Module Extremely short orbital periods are observed for many exoplanets: Many Jupiter-size and larger objects with periods of a few days. Orbits of Extrasolar Systems Module Many planets are on highly eccentric orbits close to their host stars. Eccentricities can be much higher compared to solar-system planets. Possible Types of Exoplanets Module Masses of planets set into context with their thermal environments. Status: Oct 2013. The Habitable Zone Module Habitable zone is shifted corresponding to the star’s luminosity. Example: Gliese 581 Exoplanet Survey: Super-Earths Module Copyright: DLR - H. Rauer Currently known (as of early 2014) super-Earth exoplanets (1 < m ≤ 10 MEarth or rplanet ≤ 3 REarth) for different host star masses in comparison to the position of the habitable zone (green). PLATO will be able to detect and characterise hundreds of super-Earths in the habitable zone up to ~1 AU. The planets of our Solar System are shown for reference. Overview Module Introduction to Extrasolar Systems Exoplanet Hunting Geophysics of Extrasolar Planets Specific Applications Major Open Questions Future Exploration Ground-based Campaigns and Missions Ground-based Campaigns Module AAPS, APF, CORALIE, EAPSNet, ELODIE, EPICS, ESPRESSO, FINDS Exo- Earths, Geneva (HARPS, HARPS-N), GPI, HATNet, HEK, HiCIAO, HIRES, KELT, LCES, Magellan, MARVELS, Mearth, MicroFUN, MOA, N2K, NESSI, OGLE, OPSP, PlanetPol, PlanetQuest, Project 1640, PARAS, SEEDS, SETI, SOPHIE, SuperWASP, Systemic, TrES, XO Telescope, ZIMPOL/CHEOPS Space missions (past and current) MOST (2003–present); Canadian Mission, follow-up observations, e.g. 55 Cnc e SWEEPS (2006) (HST Campaign), COROT (2006–2013), CNES/ESA EPOCh (2008–2013) former Deep Impact Vehicle Kepler (2009–present), Gaia (2013–present) Space Missions (planned) CHEOPS (2017), TESS (2017), James Webb Space Telescope (2018) · PLATO (2024) Missions Module NASA Roadmap Missions: COROT Module COROT: COnvection, ROtation et Transits planétaires CNES, ESA Launch: 2006 Life-time: 7 years Detection Method: Transit Astro-seismology and search for exoplanets. COROT has detected 14 exoplanets. The planet COROT 7b has a mass of only 4.8 Earth masses. It is a terrestrial planet with an orbital period of about 11 hours. Missions: Kepler Module NASA Launch: March 2009 Life-time: over 5 years (as of July 2014) Detection Method: Transit 95 cm telescope Search for habitable planets. Kepler has detected more than 420 planets (as of July 2014) and several thousand planet candidates that have not yet been confirmed by follow-up observations. Overview Module Introduction to Extrasolar Systems Exoplanet Hunting Geophysics of Extrasolar Planets Specific Applications Major Open Questions Future Exploration Geophysical Aspects Module Mass-Radius Relationship Equations of state and interior structure models Thermal state and internal dynamics Rotation states and tidal heating However: (a) Data sets are very limited (mainly mass and radius) (b) A broad parameter space has to be investigated to derive robust solutions from modeling. (c) Classical geophysical methods (e.g., gravity field determination, seismology) are not applicable. (d) Stellar environments can be very different from the solar system environment. Mass-Radius Relations Module … impose constraints on planet atmosphere and interior models. … can be used to infer bulk compositions and volatile contents. … help characterize diversity of super-Earths. Knowledge of mass, radius and orbital period are prerequisites to better understand planet formation, interior evolution, orbit migration, orbital resonances and tidal heating. Available mass and radius measurements for more than 100 exoplanets with continuously growing data-sets. Observational data base is rapidly growing by ongoing and future space telescope surveys such as Kepler and PLATO. Transit method Doppler spectroscopy (CoRoT, Kepler, PLATO) (HARPS,ESPRESSO)