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
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)
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
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
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
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
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
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
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
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
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)
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.
O2 Buildup on Known Exoplanets
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
Thank youarXiv:1411.7412