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Manuel Güdel ETH Zürich Switzerland With Michael Meyer & Hans Martin Schmid Habitable Planets: Targets and their Environments Pathways, Barcelona, 15 September.

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Presentation on theme: "Manuel Güdel ETH Zürich Switzerland With Michael Meyer & Hans Martin Schmid Habitable Planets: Targets and their Environments Pathways, Barcelona, 15 September."— Presentation transcript:

1 Manuel Güdel ETH Zürich Switzerland With Michael Meyer & Hans Martin Schmid Habitable Planets: Targets and their Environments Pathways, Barcelona, 15 September 2009

2 Not discussed here: Star and planet formation, disks & gaps/migration/zodi light : see M. Meyers talk Galactic population statistics Geophysical issues Outline THE STARS: What role for planetary habitability? (luminosity, age, metallicity, high-energy radiation and particles) Pathways, Barcelona, 15 September 2009

3 Luminosity Toward smaller HZ: less perturbation by Jupiters & companions and: low-mass stars have fewer Jupiters (Endl et al. 03, Butler et al. 07) stable orbits & conditions Spec.Luminosity HZ Type(L )radius (AU) (Unsöld & Baschek) (Kasting & Catling 03) A054 4 F G K M M M G, K (Scalo et al. 2007) (Kasting & Catling 03) Pathways, Barcelona, 15 September 2009 classical definition of HZ log m

4 Metallicity High-[Fe/H] stars more likely to host Jupiter-like planets Not true for Neptunes/Super-Earths (more easily found around low [Fe/H] stars; Sousa et al. 2008, Mayor et al. 2009) However: Earth-like planetary mass in solar system 2M E [Fe/H] -0.3 (Turnbull 08) requirement: stars in young disk population (Fischer & Valenti 2005) Neptunes (Sousa et al. 2008) Pathways, Barcelona, 15 September 2009

5 Age Age can be estimated from position in HRD, from rotation period, or from magnetic activity. Spec.Massmain sequence Type(M ) lifetime (Gyr) A030.39too short for biology F still short… G (>30% evolutionary change in L bol ) K M00.548very slow evolution stable HZ Con-M: Evolution toward MS very slow as well: on MS with stable HZ only after 1 Gyr for 0.1M (Burrows et al. 2001) (Unsöld & Baschek) Pathways, Barcelona, 15 September 2009

6 The Young Sun was a Fainter Star.... (Sackmann & Boothroyd 2003) 30% Deep freeze on young Earth and Mars? Do other wavelength matter here? Pathways, Barcelona, 15 September 2009

7 The "Young Active Sun": Non-Flaring Emission Wavelength-Dependent Evolution (Guinan & Ribas 2002)(Ribas, Guinan, Guedel 2005) age soft X EUV UV soft X EUV UV optical Luminosity decay more rapid over much larger scale in X-rays than in UV (while optical radiation is increasing) Pathways, Barcelona, 15 September 2009

8 M dwarf photospheres L U,V = 3x M dwarf chromosphere Irradiance Normalized to HZ Even active M dwarfs show lower UV in their HZ outside flares (Segura et al. 2005, Scalo et al. 2007) Different photochemistry: Less molecule formation (OH) or destruction (CH 4, N 2 O) Good bioindicator! (Segura et al. 2005) Greenhouse gas! HZ? Pathways, Barcelona, 15 September 2009

9 Continuous Flaring 300Myr (Audard et al. 2003) (Telleschi, Guedel et al. 2005) UV Cet M5.5 G1 Pathways, Barcelona, 15 September 2009

10 EUV flare rate (above erg) L X (Audard, Guedel, et al. 2000) Flares: L UV L X for biologically relevant UV (Mitra-Kraev, Harra, Guedel et al. 2005) Slope 1.17±0.05 ( Å) Pathways, Barcelona, 15 September 2009

11 XUV flare rate above a given threshold decreases with - decreasing mass - increasing age as does the overall emission E ( keV) N (>E) per day (Audard, Guedel, et al. 2000) age mass GK M M G Pathways, Barcelona, 15 September 2009

12 G and M dwarf flares physically/spectrally similar, related to L X But: larger relative modulation in UV domain (Segura et al. 2005, Scalo et al. 2007) : consequence for (non-equilibrium) atmospheric photochemistry or life? Dependent on amplitudes? Sun M Dwarfs (Scalo et al. 2007) 50-70% Hα active (West et al. 04, see also Silvestri et al. 05, Feigelson et al. 04) normalized L X M stars stay at a relatively high (X-ray) activity level for a longer time Pathways, Barcelona, 15 September 2009

13 Evaporation of Planetary Atmospheres < 1700 Å heats thermosphere (by photoioniz./dissociation) mv 2 /2 > GMm/R: particle escapes: up to several bars! Exosphere: mean free path > local scale height dissociation H 2 O 2H + O (+ further reactions) Loss of large amounts of water EUV Thermosphere Exosphere T exo __ Earth Mars 500km 210km 90km 90km blow-off (Kulikov et al. 2007) Mars (eg, Watson 1981, Kasting & Pollack 1983, Chassefiere & Leblanc 2004, Kulikov et al. 2007, Tian et al. 2008)

14 Semi-Empirical Mass-Loss Estimates for the Young Sun Further, Coronal Mass Ejections in active stars act like continuous wind (500 km/s, 10 3 cm -3 ) (Khodachenko et al. 2007, Lammer et al. 2007) (Wood et al. 2005) old youngyoung old age Wind mass loss decreases with age: dM/dt t -2.3 Pathways, Barcelona, 15 September 2009

15 Wind CME UV Dissociative recombination Molecule ionization, recombination fast neutrals Sputtering Ions reimpact atmosphere eject molecules Ion pickup Impact ionization + charge exchange, E and B fields atmospheric loss Interaction atmosphere – environment (solar wind) Nonthermal Escape Pathways, Barcelona, 15 September 2009 (see, e.g., Lammer et al. 2003, Lundin & Barabas 2004, Lundin et al. 2007)

16 M star HZ closer to star planets may rotate synchronously (Grieβmeier et al. 2005) synchronous rotation weaker magnetospheric shielding smaller distance Pathways, Barcelona, 15 September 2009

17 Tidal Locking and Magnetospheres & denser stellar wind weaker magnetic shielding stronger cosmic ray flux more NO x production ozone destruction biological damage? or evolutionary driver? (Grieβmeier et al. 2005) Earth M dwarf planet & high activity & flares continuous CMEs EUV heating atmospheric expansion small magnetospheric standoff distance atmospheric erosion for M dwarf planets, 10s to 100s of bars (Khodachenko et al. 2007, Lammer et al. 2007)

18 Pathways, Barcelona, 15 September 2009 To make a planet habitable.... Watch out for the host stars! optical spectrum and luminosity traditional HZ planetary rotation (locked?) magnetic moment of planet metallicity formation of terrestrial planets age/evolutionary scales usefulness of HZ for life XUV activity heating/ionizing upper atmosphere atmosph. photochemistry atmospheric erosion XUV variability non-equilibrium atmospheres? winds, CMEs, particles ionisation, erosion

19 END


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