The Physics of Exoplanets

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1 The Physics of Exoplanets Heike Rauer Institut für Planetenforschung, DLR, Berlin-Adlershof, Zentrum für Astronomie und Astrophysik, TU Berlin

2 Formation in protoplanetary disk, migration Loss of primary, atmosphere Stellar radiation, wind and magnetic field Cooling, differentiation Cooling, differentiation life Secondary atmosphere (plate)- tectonics H. Rauer

3 Characterizing the physical parameters of a planet Characterizing exoplanets: needs characterization of stars: Mass, radius, mean density Stellar mass, radius (gaseous, rocky, composition, interior) (constrain planet parameters) Orbital distance, atmosphere Stellar type and activity (habitability) (define stellar insolation) Age Stellar age (planet and planet system evolution) (defines planet age)

4 Planet detection: status Small planets are more numerous than gas giants New types of planets, e.g.: Hot Jupiters Mini-Neptunes Super-Earths Fressin et al. 2013

5 Kepler 90: A system with 7 planets Solar System Kepler 90 5 small inner planets, 2 giants Architecture shows some similarity to the Solar System Cabrera et al., 2013; Schmitt et al a [AU] radius (R earth ) Super-Earths Mini-Neptunes Gas giants

6 Do we know potentially habitable exoplanets?? The development of life needs liquid surface water: Surface Moderate temperatures

7 super-earths

8 super-earths

9 Mass-radius of planets in the super- Earth regime Light/small planets found which indicate extended (hydrogen) atmospheres Gaseous exoplanets can be as small or light as rocky planets. Typical planet classes as found in the Solar System are not the general rule.

10 Status: detected super-earths

11 Super-Earths with known radius and mass No secured rocky planets known in the habitable zone today!

12 How to separate mini-neptunes from rocky planets? Measure mass and radius: mean density! Also need accurate stellar parameters!

13 Planet formation and evolution Not all density-mass combinations are realized. One order-of-magnitude diversity in mean density found for a given mass. Indicates critical core mass around 9-10 M earth Need to verify supermassive rocky planets First indications for low-mass planets with extended hydrogen atmospheres, as predicted by planet synthsis models

14 Gas giants Gas giants contract with age A population of gas giants with heavy cores has been found CoRoT-13b 140 M earth Inflated planets 300 M earth Cabrera et al. 2010

15 Planets at intermediate distances All known planets with measured mean densities. Exolanets with measured mean densities and P 50 days hot temperate Planets at intermediate distances: are less affected by stellar radiation and winds (e.g. heating, atmospheric losses, ) allow for temperate climate, hence habitable conditions. are less affected by tidal forces (e.g. dynamical evolution) Probe different formation regions

16 The next steps towards habitable planets CHEOPS TESS Mercury K2

17 The PLATO Mission Mission proposal for ESA M3 launch selection The instrument: 32 «normal» cameras : cadence 25 sec 2 «fast» cameras : cadence 2.5 sec, 2 colours pupil: 120 mm dynamical range: 4 m V 13(16) The methods Example: Kepler-10b Characterize planets around solar-like stars: radius up to 2% mass up to 10% age known to 10%

18 Observation strategy and sky coverage 1. two long pointings : 3 years or 2 years 2. «step&stare» phase (1 or 2 years) : N fields 2-5 months each Kepler PLATO long pointing CoRoT CoRoT PLATO step&stare PLATO long pointing >50% of the sky

19 ~ stars with asteroseismology ~ accurate lightcurves Complement Gaia Detection and characterization performance for Earth-like planets ~ super-earths transits in the HZ of solar-like to cool dwarfs Thousands of mini-neptunes and gas giants. Moons, rings, exocomets Ages of planetary systems Planets around sub-giants, giants, post RGB stars, circumbinaries, AU AU Habitable zone of solar-like stars Stellar science: Stellar structure and evolution Red giants, clusters, classical pulsators, activity and flaring,

20 The next steps towards habitable planets

21 Summary The diversity of planets and planetary systems is large, and the Solar System planets do not serve as a general analogue Identifying potentially habitable planets needs secure identification of planet nature (rocky versus mini-neptune ) Need to understand planet diversity to understand planet formation Requires well charcterized stars Space missions launched until ~2020 will cover close-in planets. Going beyond needs PLATO 2.0 > putting the Solar System into context.

22 More to come