Energy-limited escape revisited: A transition from strong planetary - PowerPoint PPT Presentation

Energy-limited escape revisited: A transition from strong planetary winds to stable thermospheres Michael Salz 1 , P. C. Schneider, S. Czesla, J. H. M. M. Schmitt 1Hamburger Sternwarte, Universität Hamburg msalz@hs.uni-hamburg.de OHP 2015 : Twenty years of giant exoplanets - October 8, 2015

Hot gas planets WASP-12 distance < 0.1 AU (Mercury: 0.4 AU) irradiation level: 10 2 - 10 5 times Earth's → hot expanded atmospheres Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

Formation of a planetary wind WASP-12 eff. grav. potential Roche lobe high-energy irrad. causes continuous atmos. expansion → a planetary wind develops → persistent mass-loss Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

Energy-limited mass loss energy conservation: area: A absorbed energy is converted F EUV to gravitational potential energy → mass loss: . A ⨉ F EUV ) ( cm 2 erg/(cm 2 s 1) g = M = ΔΦ G erg/g s R pl R Rl Gravitational potential heating efficiency correction: η . ΔΦ G A ⨉ η ⨉ F EUV = M ΔΦ G (e.g., Erkaev et al. 2007) Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

Observational evidence HD 209458 planet → 1.5 % R = 2.63 Rpl → 10 % • first evidence: ∼ 10% Lyα absorption in HD 209458 b (Vidal-Madjar et al. 2003) • confirmed in 5 more obs. (H, C, O, Si, Mg) • expanded atmospheres: HD 189733 b, WASP-12 b, GJ 436 b (indications in 55 Cnc b) Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

Complex environment stellar wind confinement photoevaporation magnetic confinement stellar wind interaction + radiation pressure → cometary tail → no generally accepted theory Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

Approach 1D HD simulations of spherically symmetric planetary winds new: • all systems in the solar neighborhood • detailed photoionization solver Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

Approach 1D HD simulations of spherically symmetric planetary winds new: • all systems in the solar neighborhood • detailed photoionization solver = TPCI PLUTO + CLOUDY hydrodynamics: photoionization solver: • 1D spherical grid • equilibrium state of medium • gravity under strong irradiation • thermal • absorption and emission conduction Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

Atmosphere of HD 209458 b 10 13 10 13 HD 209458 b HD 209458 b Density (cm -3 ) Density (cm -3 ) 10 10 10 10 10 7 10 7 Temp. (1000 K) Temp. (1000 K) 10 10 6 6 2 2 10 1 10 1 Velocity (km s -1 ) Velocity (km s -1 ) 10 -1 10 -1 10 -3 10 -3 1 1 2 2 3 3 4 4 5 5 Radius (R pl ) Radius (R pl ) Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

HD 209458 b and HD 189733 b 10 13 10 13 HD 209458 b HD 209458 b Density (cm -3 ) Density (cm -3 ) HD 189733 b HD 189733 b 10 10 10 10 10 7 10 7 Temp. (1000 K) Temp. (1000 K) 10 10 6 6 2 2 10 1 10 1 Velocity (km s -1 ) Velocity (km s -1 ) 10 -1 10 -1 10 -3 10 -3 1 1 2 2 3 3 4 4 5 5 Radius (R pl ) Radius (R pl ) Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

HD 209458 b and HD 189733 b HD 189733 b irradiation 16 times higher - Why wind weaker? free-free free-free Ly α Ly α emission emission (heating - cooling)/heating (heating - cooling)/heating 1.0 1.0 0.5 0.5 HD 209458 b HD 209458 b HD 189733 b HD 189733 b 0.0 0.0 1 1 2 2 3 3 4 4 5 5 Radius (R pl ) Radius (R pl ) → strong radiative cooling → η eff different Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

Revised energy-limited escape higher gravity → hotter atmosphere → more rad. cooling → smaller η eff WASP-77 b WASP-77 b WASP-43 b WASP-43 b CoRoT-2 b CoRoT-2 b -1 -1 log 10 ( η eva ) log 10 ( η eva ) -2 -2 HD 209458 b HD 209458 b HD 189733 b HD 189733 b -3 -3 HD 149026b HD 149026b HD 97658 b HD 97658 b HAT-P-11 b HAT-P-11 b WASP-80 b WASP-80 b WASP-12 b WASP-12 b GJ 1214 b GJ 1214 b GJ 3470 b GJ 3470 b 55 Cnc e 55 Cnc e GJ 436 b GJ 436 b -4 -4 stable atmos. -5 -5 12.2 12.2 12.4 12.4 12.6 12.6 12.8 12.8 13 13 13.2 13.2 13.4 13.4 13.6 13.6 log 10 ( Φ G ) (erg g -1 ) log 10 ( Φ G ) (erg g -1 ) → a scaling law: η eff = η eff (Φ G ) . A ⨉ η ⨉ F EUV → estimates for the mass-loss rates: M = ΔΦ G (not only upper limits) valid for mini-Neptunes to massive hot Jupiters Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

Energy-limited escape revisited absorption small planets: strong Lyα absorption versus emission GJ 1214 GJ 1214 (M. Salz) GJ 3470 GJ 3470 HD 97658 HD 97658 55 Cnc e 55 Cnc e 12.5 12.5 GJ 436 GJ 436 HAT-P-11 HAT-P-11 log 10 ( Φ G ) (erg g -1 ) log 10 ( Φ G ) (erg g -1 ) HD 209458 HD 209458 HD 149026 HD 149026 13 13 WASP-80 WASP-80 WASP-12 WASP-12 HD 189733 HD 189733 WASP-77 WASP-77 13.5 13.5 WASP-43 WASP-43 WASP-8 WASP-8 CoRoT-2 CoRoT-2 WASP-10 WASP-10 14 14 HAT-P-2 HAT-P-2 HAT-P-20 HAT-P-20 massive planets: absorption 100 100 10 10 1 1 little OHP – October 8, 2015 Ly α absorption (%) Ly α absorption (%)

Energy-limited escape revisited absorption small planets: strong Lyα absorption versus emission Ly α emission (%) Ly α emission (%) emission 10 -3 10 -3 10 -2 10 -2 little 0.1 0.1 10 10 1 1 → verify the hydrodynamic escape model GJ 1214 GJ 1214 (M. Salz) GJ 3470 GJ 3470 HD 97658 HD 97658 55 Cnc e 55 Cnc e 12.5 12.5 GJ 436 GJ 436 HAT-P-11 HAT-P-11 log 10 ( Φ G ) (erg g -1 ) log 10 ( Φ G ) (erg g -1 ) HD 209458 HD 209458 HD 149026 HD 149026 13 13 WASP-80 WASP-80 WASP-12 WASP-12 HD 189733 HD 189733 WASP-77 WASP-77 13.5 13.5 WASP-43 WASP-43 WASP-8 WASP-8 CoRoT-2 CoRoT-2 WASP-10 WASP-10 14 14 HAT-P-2 HAT-P-2 HAT-P-20 HAT-P-20 massive planets: absorption 100 100 10 10 1 1 little OHP – October 8, 2015 Ly α absorption (%) Ly α absorption (%) emission strong

Summary Simulations of planetary winds in solar neighborhood: • strong radiative cooling in massive planets → new scaling law for heating efficiency → mass-loss estimates for all hot gas planets • Lyα absorption and emission signals → show trend depending on grav. potential → can be tested observationally Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

Outlook Simulations: • include metals in the simulations → compute metal absorption and compare with obs. • simulate molecular outflow in planets further out (55 Cnc b, Venus + Earth + Mars) • simulate full 3D picture with stellar wind and radiation pressure (GJ 436 b) Observations: • X-ray observations to characterize the irradiation • HST snapshots to identify bright host stars • transit spectroscopy of WASP-80 b Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

Motivation: Lack of hot mini-Neptunes M > 10 M E gas planets rocky planets M < 10 M E 2500 Equilibrium temperature (K) close-in 2000 evaporate 1500 1000 further out 500 0 0.1 1 10 Density (g cm -3 ) (exoplanets.org 2015, repro. according Carter et al. 2012) Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

Settling phase Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

Lyα absorption of GJ 436 b Wavelength (Å) 1,215.0 1,215.5 1,216.0 1,216.5 12 2.0 H I Lyα blue wing 10 –2 s –1 Å –1 ) –2 s –1 ) 1.5 8 10 –14 erg cm 10 –14 erg cm 6 1.0 4 Flux (× Flux (× 2 0.5 0 0 –2 –4 –2 0 2 4 29.5 30.5 –200 –100 0 100 200 Velocity (km s –1 ) Time from mid-transit (h) (Ehrenreich et al. 2015) Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

Compute Lyα absorption simulations: real situation: spherically symmetric non-symmetric + interactions host star host star unbound hydrogen h e l h e l c o c o o b o b e e R R atmosphere planet planet → absorption of atmosphere below Roche lobe can be computed → only estimate the absorption strength of unbound hydrogen (no radial velocity) total absorption depth ∼ amount of neutral hydrogen Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

Lyα absorption signals 23% 8% 3% 1% observed: verify trend → 20% 19% 10% 2% by further simulated: observations integrated absorption (± 200 km s -1 ) Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

Lyα absorption signals 23% 8% 3% 1% observed: verify trend → 20% 19% 10% 2% by further simulated: observations integrated absorption (± 200 km s -1 ) Energy-limited escape revisited (M. Salz) OHP – October 8, 2015