Mirage Earths - Rodrigo Luger · Mirage Earths Extreme Water Loss and Abiotic O 2 Buildup on...
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Mirage EarthsExtreme Water Loss and Abiotic O2Buildup on Planets Throughout the
Habitable Zones of M Dwarfs
Rodrigo Luger and Rory Barnes
225th AAS — January 8, 2015
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The Big Picture
M dwarfs: the best targets Terrestrial planets are easiest todetect around low-mass stars
Rapid planet formation Both in situ formation and disk-driven migration into the HZoccur in . 10 Myr
Extended pre-MS phase M dwarfs can take up to ∼ 1Gyr to reach the main sequence
Long activity timescales High X-ray/EUV fluxes in theHZ for up to a few Gyr
Scalo et al. (2007), Ricker et al. (2010)
Raymond et al. (2007), Lissauer (2007)
Baraffe et al. (1998), Lissauer (2007)
Scalo et al. (2007), West et al. (2008)
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Pre-Main Sequence Evolution
106 107 108 109 1010
time (years)
0.01
0.10
1.00se
mi-
majo
r axis
(A
U)
Habitable
Too Hot
Earth today
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Pre-Main Sequence Evolution
106 107 108 109 1010
time (years)
0.01
0.10
1.00se
mi-
majo
r axis
(A
U)
Habitable
Too Hot
Earth todayEarth formed
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Pre-Main Sequence Evolution
106 107 108 109 1010
time (years)
0.01
0.10
1.00se
mi-
majo
r axis
(A
U)
1.001.001.001.00
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Pre-Main Sequence Evolution
106 107 108 109 1010
time (years)
0.01
0.10
1.00se
mi-
majo
r axis
(A
U)
1.001.001.001.00
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.15
0.10
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Pre-Main Sequence Evolution
106 107 108 109 1010
time (years)
0.01
0.10
1.00se
mi-
majo
r axis
(A
U)
1.00
0.10
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Pre-Main Sequence Evolution
106 107 108 109 1010
time (years)
0.01
0.10
1.00se
mi-
majo
r axis
(A
U)
Earth today
Exo-Earth today
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Pre-Main Sequence Evolution
106 107 108 109 1010
time (years)
0.01
0.10
1.00se
mi-
majo
r axis
(A
U)
Earth todayEarth formed
Exo-Earth todayExo-Earth formed
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Duration of the Runaway Greenhouse
0.01 0.1 1.0
a (AU)
0.1
0.2
0.3
0.4
0.5
0.6
0.70.80.9
M(M
¯)
1 Myr
10 Myr
100 Myr
1 Gyr
5 Gyr
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Atmospheric Escape Model
XUV power law decline (Ribas et al. 2005)
LXUV
Lbol=
{f0 t ≤ t0
f0(
tt0
)−β
t > t0(1)
XUV-driven energy-limited escape (Erkaev et al. 2007)
FH =εXUVFXUVRp
4GMpKtidemH(2)
Hydrodynamic mass fractionation (Hunten et al. 1987)
FO =XO
XHFH
(mc −mO
mc −mH
)(3)
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Water Loss & O2 Buildup
RV 25% 50% 75% EM
Position in Habitable Zone
0.1
0.2
0.3
0.4
0.5
0.6
0.70.80.9
M(M
¯)
0.1
1
10
∆M
H2O
(TO
)RV 25% 50% 75% EM
Position in Habitable Zone
0.1
0.2
0.3
0.4
0.5
0.6
0.70.80.9
M(M
¯)
1
10
100
1000
5000
PO
2(b
ar)
A 5 M⊕ super-Earth can lose up to a few tens of Earth oceans ofwater and build up several thousands of bars of O2, particularlynear the inner HZ of low-mass M dwarfs.
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O2 Buildup on Known Exoplanets
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Summary & Conclusions
Planets in the HZs of all M dwarfs can lose several Earthoceans of water and build up hundreds to thousands of barsof O2. Both processes threaten the habitability of many ter-restrial planets
Water loss scales with planet mass. Super-Earths lose morewater than Earths because of inhibited oxygen escape
O2 buildup rates also scale with planet mass: ∼ 5 bars/Myron Earths and ∼ 25 bars/Myr on super-Earths. These rates arecontrolled by diffusion
Fast O2 production could overwhelm surface sinks, leading todetectable levels of atmospheric O2. Oxygen may not be areliable biosignature on M dwarf planets
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Thank youarXiv:1411.7412