Download What makes a planet habitable?

What makes a planet habitable?
Helmut Lammer
[ISSI Team evolution and characterization of habitable planets
& research stimulated within Europlanet DWGs & IWF related bilateral projects]
Austrian Academy of Sciences, Space Research Institute (IWF)
Schmiedlstr. 6, A-8042 Graz, Austria
(email: [email protected])
IWF/ÖAW GRAZ
1
A classification for habitats
[Lammer et al., to be submitted to Astron. Astrophys. Rev., 2008]
Water-rich bodies
at the beginning
Class. I
E
M
V
Venus
-like
Icy
moons
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Evolutionary time line
Classical habitable zone
Class. II
Inner and outer edge of the
habitable zone or habitable
zones of low mass stars
Class. III
Beyond the ice-line
Earth-like
Mars
-like
Habitats suitable for the
evolution of higher life
forms on the surface
Microbial life may have
evolved and habitats in
subsurface, ice/H2O, may
have remained
Life forms may have evolved
Europalike
and populate subsurface
H2O oceans
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A classification for habitats
[Lammer et al., to be submitted to Astron. Astrophys. Rev., 2008]
Water-rich bodies
at the beginning
Class. I
E
M
V
Evolutionary time line
Venus
-like
Icy
moons
Classical habitable zone
Class. II
Inner and outer edge of the
habitable zone or habitable
zones of low mass stars
Class. III
Beyond the ice-line
Earth-like
Mars
-like
Habitats suitable for the
evolution of higher life
forms on the surface
Microbial life may have
evolved and habitats in
subsurface, ice/H2O, may
have remained
Life forms may have evolved
Europalike
and populate subsurface
H2O oceans
Migrating “super-Europa’s”,
Class. IV
IWF/ÖAW GRAZ
Ice-rich exoplanets
which migrate inside
a habitable zone or
“hot ice giants”,
“Ocean planets”
Lower or/and higher
life may evolve but
2
Earth: A geodynamic active planet/habitat
IWF/ÖAW GRAZ
3
Geophysical relevance of water:
Convecting mantle
Efficient cooling
Large amount of
⇒ H2O in the mantle is
Regassing
important ! (Oceans)
Volcanism
Dynamo Action
Subduction
Crust
Degassing
Magnetosphere
Shielding
Hydros- + Cryosphere
Biosphere
Atmosphere
From D. Breuer, DLR, Berlin
IWF/ÖAW GRAZ
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The magnetic protection of Earth´s
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5
One plate planets (present Venus and
Convecting mantle
Very hot (dry) or
frozen planets
(inner and outer
Inefficient cooling
boundary of the
Volcanism
Dynamo Action
classical habitable
zone)
Crust
Degassing
Magnetosphere
Shielding
Hydros- + Cryosphere
Atmosphere
Biosphere
?
Space
From D. Breuer, DLR, Berlin
IWF/ÖAW GRAZ
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One plate planets (present Venus and
Convecting mantle
Very hot (dry) or
frozen planets
(inner and outer
Inefficient cooling
boundary of the
Volcanism
Dynamo Action
classical habitable
zone)
Crust
Degassing
Magnetosphere
Shielding
Hydros- + Cryosphere
Atmosphere
Biosphere
?
Space
From D. Breuer, DLR, Berlin
IWF/ÖAW GRAZ
6
One plate planets (present Venus and
Convecting mantle
Very hot (dry) or
frozen planets
(inner and outer
Inefficient cooling
boundary of the
Volcanism
Dynamo Action
classical habitable
zone)
Crust
Degassing
Magnetosphere
Shielding
Hydros- + Cryosphere
Atmosphere
Biosphere
?
Space
From D. Breuer, DLR, Berlin
IWF/ÖAW GRAZ
6
One plate planets (present Venus and
Convecting mantle
Very hot (dry) or
frozen planets
(inner and outer
Inefficient cooling
boundary of the
Volcanism
Dynamo Action
classical habitable
zone)
Crust
Degassing
Magnetosphere
Shielding
Hydros- + Cryosphere
Atmosphere
Biosphere
?
Erosion by solar/stellar plasma flow
Space
From D. Breuer, DLR, Berlin
IWF/ÖAW GRAZ
6
No magnetic atmosphere protection
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Solar/stellar-planetary relations and their
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The young Sun I (G stars): → total luminosity
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[Guinan and Ribas: ASP, 269, 85 – 107, 2002]
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The young Sun/stars II: → solar/stellar winds
[Ribas et al.: ApJ 622, 680 – 694, 2005]
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10
The young Sun/stars II: → solar/stellar winds
→ Maximum expected
→ Average expected
→ Minimum expected
®Sudden cut-off ?
[Ribas et al.: ApJ 622, 680 – 694, 2005]
[Wood et al.: ApJ 574, 412 –425, 2002;
Kulikov et al.: PSS, 54, 1425, 2006]
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10
The young Sun/stars II: → solar/stellar winds
→ Maximum expected
→ Average expected
→ Minimum expected
®Sudden cut-off ?
[Ribas et al.: ApJ 622, 680 – 694, 2005]
[Newkirk, Jr.: Geochi. Cosmochi. Acta Suppl., 13, 293–301;
Kulikov et al.: PSS,
54, 1325,
[Wood
et al.: 2006]
ApJ 574, 412 –425, 2002;
Kulikov et al.: PSS, 54, 1425, 2006]
IWF/ÖAW GRAZ
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The young Sun (G stars) III: → X-ray and EUV
EK Dra
(100 Myr)
p1 UMa
(300 Myr)
k1 Cet
(650 Myr)
Sun
(4.56 Gyr)
[Ribas et al.: ApJ, 622, 680 – 694, 2005]
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The upper atmosphere (Thermosphere,
exosphe
exobase
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Thermospheric heating and cooling processes
 The most important heating and cooling processes in the upper
atmosphere of Earth can be summarized as follows
[e..g., Dickinson, 1972; Chandra and Sinha, 1974; Gordiets et al., 1978; Gordiets et al., 1981;
Gordiets et al., 1982; Dickinson et al., 1987]

heating due to O2, N2, and O photoionization by solar XUV
radiation ( λ ≤ 1027 Å),

heating due to O2 and O3 photodissociation by solar UV radiation
(1250 ≤ λ ≤ 3500 Å),

chemical heating in exothermic binary and 3-body reactions,

neutral gas molecular heat conduction,
IWF/ÖAW GRAZ
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Time evolution of the exobase temperature based
on Earth's present atmospheric composition
?
Hydrostatic equilibrium is assumed
→no hydrodynamic flow and
adiabatic cooling
5000 K (H atoms)
[Kulikov et al., SpSciRev., 2007]

The blow-off temperature for atomic hydrogen of about 5000 K would
be exceded during the first Gyr

For XUV fluxes more than 10 times the present flux (> 3.8 Gyr ago) one
would expect extremely high exospheric temperatures
IWF/ÖAW GRAZ
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Time evolution of the exobase temperature based
on Earth's present atmospheric composition
?
Hydrostatic equilibrium is assumed
→no hydrodynamic flow and
adiabatic cooling
CO ?
2
5000 K (H atoms)
[Kulikov et al., SpSciRev., 2007]

The blow-off temperature for atomic hydrogen of about 5000 K would
be exceded during the first Gyr

For XUV fluxes more than 10 times the present flux (> 3.8 Gyr ago) one
would expect extremely high exospheric temperatures
IWF/ÖAW GRAZ
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Expected scenarios of atmosphere responses
present Earth
composition
(Earth)
[Lammer et al., Space Sci. Rev.,
in press, 2008; Tian et al., JGR,
in press, 2008]
[Kulikov et al., Planet. Space Sci.,
54, 1425 – 1444, 2006]
96 % CO2
atmosphere
(Venus)
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M stars and radiation activity
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X-ray/EUV activity of low mass stars
Early
Venus, Earth, Mars,
Titan, gas giants,
comets
0.1 Gyr
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Exoplanets
0.3 Gyr
1.0 Gyr
[Scalo et al., Astrobiology, 7, 85, 2007]
3.16 Gyr
10 Gyr
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Soft X-ray and EUV induced expansion of the upper
atmospheres can lead to high non-thermal loss rates
present
Venus,
Mars
present Earth
[Lammer et al., Astrobiology, 7, 185, 2007]
IWF/ÖAW GRAZ
Early Earth ?
terrestrial
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Its not so simple! →No analogy for habitable
zones of lower mass stars (K and M-types)
Atmospheric effects and
habitability of Earth-like
exoplanets within close-in
habitable zones
 Enhanced EUV and X-rays
 Neutron fluxes
 Coronal mass ejections
(CMEs)
 Intense solar
proton/electron fluxes
(e.g., SPEs)
Solar – stellar analogy
 Data from Sun + Stars
Space and ground-based data
 Correlated analysis of events
IWF/ÖAW GRAZ
 Establishing an extreme event data-base
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Plasma environment within close-in habitable
zones
0.05 AU
0.1 AU
0.2 AU
1 AU
nmin (d) = 4.88 d/d0
-2.31
nmax(d) = 7.10 d/d0
-2.99
v
mod
CME
= 1 AU
= 450d0km/s
[Khodachenko et al., Astrobiology, 7,167, 2007]

White light [Vourlidas, et al., ESA SP-506, 1, 91, 2002]
 Radio
[Gopalswamy and Kundu, Solar Phys., 143, 327, 1993]

UV [Ciaravella, et al., ApJ., 597, 1118, 2003]
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similar values at 3-5 RSun:
nCME ~106 cm
–3
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Plasma environment within close-in
habitable zones
IWF/ÖAW GRAZ
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Hot and background O atoms as function of
IP
O2 + e → O + O + ΔE
+
*
*
IP
[Kulikov et al., Planet. Space Sci., 54, 1425, 2006]
→Extreme plasma interaction with extended atmosphere
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3D MHD simulation of Venus solar wind
interaction with present & extreme conditions
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3D MHD simulation of Venus solar wind
interaction with present & extreme conditions
IWF/ÖAW GRAZ
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O+ loss rates of present Venus at 0.7 AU
Venus
Express
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O+ loss rates of present Venus at 0.7 AU
Venus
Express
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O+ loss rates of Venus 4.25 Gyr ago; 30 XUV;
nsw=1000 cm-3 (60 × pr.) or M-star Exo-Venus at 0.3 AU
Total O+
ion loss
rate
~ 2 bar
→ 150 Myr
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O+ loss rates of Venus 4.5 Gyr ago 100 XUV;
nsw=1000 cm-3 or (active M-star) Exo-Venus at 0.3
Total O+
ion loss
rate
~ 20 bar
→ 150 Myr
26
3D MHD simulation of a Venus-like planet under
extreme stellar plasma conditions → 0.05 AU (100 XUV)
Total O+
ion loss
rate
~ 500 bar
→ 150 Myr
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Magnetospheres and model input
Rotational Effect on Magnetic Dynamo →Expected Stronger Magnetic Field
3.6 – 4 Gyr ago
[Dehant et al., Space Sci. Rev., 2007]
Plasma parameters
7 EUV: nsw ~ 90 cm-3; vsw ~780 km/s
RMagnetopause ~ 5.2 REarth → Rexo ~ 2.5REarth
RMagnetopause ~ 6.1 REarth → Rexo ~2.5REarth
10 EUV: nsw ~ 200 cm-3; vsw ~ 900 km/s
RMagnetopause ~ 5.2 REarth → Rexo ~ 4.8REarth
20 EUV: nsw ~ 270 cm-3; vsw ~1010 km/s
RMagnetopause ~ 4.7 REarth → Rexo ~ 12.7REarth
IWF/ÖAW GRAZ
Estimated magnetic
moment of early Earth, relative to
its present-day value, as a
function of possible early
planetary rotation periods in
hours. The dotted vertical line
denotes the present-day sidereal
M star planets may have weak
rotation rate of the Earth
magentic moments → slow rotation
Ionization processes in the extended
exosphere(s)
Solar
Solar EUV:
wind hν
charge
+N→
exchange:
N + + ep+ + N → N+ + HENA
Electron impact ionization:
e- + N → N+ + 2e-
Cummings et al. ApJ 578:194, [2002]
NIFS data base:
28
http://dpc.nifs.ac.jp/aladin/
Test-particle model results of N+ pick up ion
7EUV (3.8 Gyr ago)
20EUV (4.13 Gyr
ago)
Exosphere density
above the exobase is
calcuated from
Chamberlain`s theory
Parometric law
modified with particion
functions [Chamberlain,
Test-particle results based on a Spreiter-Stahara model:
1963]
[e.g., Lichtenegger et al. JGR, 2001; Lammer et al., Icarus, 2003; Kulikov et al. Planet. Space Sci., 2006;
Lamme et al., Planet. Space Sci., 2006; Lammer et al. Astrobiology, 2007]
7EUV (3.6 Gyr ago), subsolar obstacle distance 6.0REarth: N+ion pick up loss rate ~ 5 ×1028 s-1
10EUV (3.8 Gyr ago): subsolar obstacle distance 5.0REarth:N+ion pick up loss rate ~5 × 1029 s-1
20EUV (4.13 Gyr ago): subsolar obstacle distance 12.7REarth N+ion pick up loss rate ~2 ×1030 s-1
Total loss of nitrogen would result in an equivalent amount of ≤ 20 bar during ~ 50 Myr
Simulations indicate that the atmosphere should have been protected more efficiently most
likely due to higher carbon-dioxide mixing ratios during the first 500 Myr after the young
Sun IWF/ÖAW
arrived
at the ZAMS
GRAZ
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H O inventories and atmospheres are strongly
2
Class I planets may
evolve to class II habitat
types at M stars
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Expected evolution of Earth’s atmosphere
Lower mass stars
K, M stars
Atmosphere evolution of Earth-like
planets will be different (low mass K
and M stars)
Sun
G stars
Earth
(G star Earth-like
planets, F star
Earth’s?)
IWF/ÖAW GRAZ
and cools the upper atmosphere so that expansion and loss rates should be reduced
31
Where are they?
Star-types and expected preferred habitats
 Class I Earth-like habitable planets may preferably be found in
orbits of Sun-like G-type and some K-type stars, F-type where the
originally defined habitable zone definition is valid → see Earth!
 Class II, III and IV habitats should also populate G-type
and F, K, and M-type stars
 Lower mass stars should have less class I habitable planets but class
II, class III and class IV habitability-types may be common like on
G-stars. Many planets which start in the habitability class I domain at
its origin may evolve to class II-types
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