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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, Universitt Hamburg msalz@hs.uni-hamburg.de OHP 2015 :

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Energy-limited escape revisited:

A transition from strong planetary winds to stable thermospheres

Michael Salz1, 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

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Hot gas planets

WASP-12

irradiation level: 102 - 105 times Earth's → hot expanded atmospheres

distance < 0.1 AU (Mercury: 0.4 AU)

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

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Formation of a planetary wind

high-energy irrad. causes continuous atmos. expansion → a planetary wind develops → persistent mass-loss

  • eff. grav. potential

Roche lobe WASP-12

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

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Energy-limited mass loss

area: A FEUV

Rpl RRl ΔΦG Gravitational potential

M

.

= A ⨉ FEUV ΔΦG

=

cm2 erg/(cm2s 1) erg/g g s

( ) heating efficiency correction: η M

.

= ΔΦG A ⨉ η ⨉ FEUV energy conservation: absorbed energy is converted to gravitational potential energy → mass loss:

(e.g., Erkaev et al. 2007)

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

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Observational evidence

  • 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)

HD 209458

planet → 1.5 % R = 2.63 Rpl → 10 %

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

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Complex environment

photoevaporation magnetic confinement stellar wind confinement stellar wind interaction + radiation pressure → cometary tail

→ no generally accepted theory

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

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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

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SLIDE 8

Approach

+ CLOUDY photoionization solver:

  • equilibrium state of medium

under strong irradiation

  • absorption and emission

PLUTO hydrodynamics:

  • 1D spherical grid
  • gravity
  • thermal

conduction

= TPCI 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

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Atmosphere of HD 209458 b

Density (cm-3) HD 209458 b 107 1010 1013

  • Temp. (1000 K)

2 6 10 Velocity (km s-1) Radius (Rpl) 10-3 10-1 101 1 2 3 4 5 Density (cm-3) HD 209458 b 107 1010 1013

  • Temp. (1000 K)

2 6 10 Velocity (km s-1) Radius (Rpl) 10-3 10-1 101 1 2 3 4 5

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

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HD 209458 b and HD 189733 b

Density (cm-3) HD 209458 b HD 189733 b 107 1010 1013

  • Temp. (1000 K)

2 6 10 Velocity (km s-1) Radius (Rpl) 10-3 10-1 101 1 2 3 4 5 Density (cm-3) HD 209458 b HD 189733 b 107 1010 1013

  • Temp. (1000 K)

2 6 10 Velocity (km s-1) Radius (Rpl) 10-3 10-1 101 1 2 3 4 5

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

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HD 209458 b and HD 189733 b

HD 189733 b irradiation 16 times higher - Why wind weaker?

free-free emission

Lyα

Radius (Rpl) HD 209458 b HD 189733 b 0.0 0.5 1.0 1 2 3 4 5

(heating - cooling)/heating

→ strong radiative cooling → ηeff different

free-free emission

Lyα

Radius (Rpl) HD 209458 b HD 189733 b 0.0 0.5 1.0 1 2 3 4 5

(heating - cooling)/heating

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

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Revised energy-limited escape

M

.

= ΔΦG A ⨉ η ⨉ FEUV → a scaling law: ηeff = ηeff(ΦG) → estimates for the mass-loss rates:

(not only upper limits)

valid for mini-Neptunes to massive hot Jupiters

stable atmos. higher gravity → hotter atmosphere → more rad. cooling → smaller ηeff

  • 5
  • 4
  • 3
  • 2
  • 1

12.2 12.4 12.6 12.8 13 13.2 13.4 13.6 log10 (ηeva) log10 (ΦG) (erg g-1)

WASP-12 b GJ 3470 b WASP-80 b HD 149026b HAT-P-11 b HD 209458 b 55 Cnc e GJ 1214 b GJ 436 b HD 189733 b HD 97658 b WASP-77 b WASP-43 b CoRoT-2 b

  • 5
  • 4
  • 3
  • 2
  • 1

12.2 12.4 12.6 12.8 13 13.2 13.4 13.6 log10 (ηeva) log10 (ΦG) (erg g-1)

WASP-12 b GJ 3470 b WASP-80 b HD 149026b HAT-P-11 b HD 209458 b 55 Cnc e GJ 1214 b GJ 436 b HD 189733 b HD 97658 b WASP-77 b WASP-43 b CoRoT-2 b Energy-limited escape revisited (M. Salz) OHP – October 8, 2015

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massive planets:

little absorption

small planets: strong absorption

12.5 13 13.5 14 1 10 100 Lyα absorption (%) log10 (ΦG) (erg g-1)

WASP-12 GJ 3470 WASP-80 HD 149026 HAT-P-11 HD 209458 55 Cnc e GJ 1214 GJ 436 HD 189733 HD 97658 WASP-77 WASP-43 CoRoT-2 WASP-10 WASP-8 HAT-P-20 HAT-P-2

12.5 13 13.5 14 1 10 100 Lyα absorption (%) log10 (ΦG) (erg g-1)

WASP-12 GJ 3470 WASP-80 HD 149026 HAT-P-11 HD 209458 55 Cnc e GJ 1214 GJ 436 HD 189733 HD 97658 WASP-77 WASP-43 CoRoT-2 WASP-10 WASP-8 HAT-P-20 HAT-P-2

Lyα absorption versus emission

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

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massive planets:

little absorption

strong emission small planets: strong absorption

little emission

→ verify the hydrodynamic escape model

12.5 13 13.5 14 1 10 100 Lyα absorption (%) log10 (ΦG) (erg g-1)

WASP-12 GJ 3470 WASP-80 HD 149026 HAT-P-11 HD 209458 55 Cnc e GJ 1214 GJ 436 HD 189733 HD 97658 WASP-77 WASP-43 CoRoT-2 WASP-10 WASP-8 HAT-P-20 HAT-P-2

12.5 13 13.5 14 1 10 100 10-3 10-2 0.1 1 10 Lyα emission (%) Lyα absorption (%) log10 (ΦG) (erg g-1)

WASP-12 GJ 3470 WASP-80 HD 149026 HAT-P-11 HD 209458 55 Cnc e GJ 1214 GJ 436 HD 189733 HD 97658 WASP-77 WASP-43 CoRoT-2 WASP-10 WASP-8 HAT-P-20 HAT-P-2

10-3 10-2 0.1 1 10 Lyα emission (%)

Lyα absorption versus emission

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

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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

Summary

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

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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

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Motivation: Lack of hot mini-Neptunes

(exoplanets.org 2015, repro. according Carter et al. 2012)

500 1000 1500 2000 2500 0.1 1 10 Equilibrium temperature (K) Density (g cm-3) M < 10 ME M > 10 ME gas planets rocky planets evaporate close-in further out

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

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Settling phase

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

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Lyα absorption of GJ 436 b

Flux (× 10–14 erg cm

–2 s–1)

2.0 1.5 1.0 0.5 H I Lyα blue wing –4 –2 2 4 29.5 30.5 Time from mid-transit (h) –200 –100 100 200 Velocity (km s–1) 1,215.0 1,215.5 1,216.0 1,216.5 Wavelength (Å) 12 10 8 6 4 2 Flux (× 10–14 erg cm

–2 s–1 Å–1)

–2

(Ehrenreich et al. 2015)

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

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simulations: spherically symmetric

host star

planet

R

  • c

h e l

  • b

e

host star

planet

R

  • c

h e l

  • b

e

atmosphere unbound hydrogen

real situation: non-symmetric + interactions → 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

Compute Lyα absorption

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

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Lyα absorption signals

verify trend by further

  • bservations

→

  • bserved:

23% 8% 3% 1% simulated: 20% 19% 10% 2%

integrated absorption (± 200 km s-1)

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

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Lyα absorption signals

verify trend by further

  • bservations

→

  • bserved:

23% 8% 3% 1% simulated: 20% 19% 10% 2%

integrated absorption (± 200 km s-1)

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