Download planets suitable for life

행성 체에
생명이 서식할 조건 : II
S.S.Hong
SNU, 05-09-18
Revised on 06-09-28
REFERENCES :
Gilmour, I. 2004, in An Introduction to ASTROBIOLOGY,
Chap 2 Habitable World, pp. 43-84.
Ulmschneider, P. 2003, in INTELLIGENT LIFE IN THE UNIVERSE,
Chap 4 Planets Suitable for Life, pp. 51-78.
Kasting, J.F., Whitmire, D.P., and Reynolds, R.T. 1993, Habitable
Zones around Main Sequence Stars, Icarus 101, 108.
S.S.Hong ; SNU 05-09-18
PLANETS SUITABLE FOR LIFE
1. HABITABLE ZONES
Solar Habitable Zone ; Habitable Zones around Other Stars
2. PLANETARY MASS, RADIUS AND TEMPERATURE
Evaporation of the Atmosphere
3. MAIN SEQUENCE LIFE TIME
4. TIDAL EFFECTS ON PLANETS
5. CONTINUOUSLY HABITABLE ZONES
6. INSTABILITIES OF THE PLANETARY ATMOSPHERE
Greenhouse; Carbon Silicate Cycle ; Irreversible Glaciation
7. AXIS VARIATIONS OF THE PLANETS
8. BIOGENIC EFFECTS ON PLANETARY ATMOSPHERE
9. THE NUMBER OF HABITABLE PLANETS
The Drake Formula ; NHP
10. DISCUSSION
S.S.Hong ; SNU 05-09-18
6. INSTABILITIES OF PLANETARY ATMOSPHERE
1) GREENHOUSE EFFECT
COMETS & VOLCANIC OUTGASSING OF UPPER MANTLE  N2, CO2, CH4, H2O
THE GREENHOUSE GAS REDUCES COOLING RATE OF THE ATMOSPHERE BY
TRAPPING IR RADIATION, WHICH IN TURN RAISES THE TEMPERATURE INSIDE.
The 100 m should be changed to 10 m .
S.S.Hong ; SNU 05-09-18
2) THE CARBON-SILCATE CYCLE
CO2 gas dissolves into H2O water to form carbonic acid H2CO3 .
H2CO3 weathers silicate rocks CaSiO3 and form calcium carbonate CaCO3 (chalk),
which in turn precipitates onto ocean floor as a solid.
IN THIS WAY CO2 CAN BE REMOVED FROM THE ATMOSPHERE IN 4 X 108 YRS .
CO2 GETS RE-SUPPLIED TO THE ATMOSPHERE BY VOLCANIC ACTIVITY.
AN IMPORTANCE OF THE PLATE TECTONICS !
+ BIOLOGICAL CYCLE
Photo-synthesis removes
CO2 gas from atmosphere;
while respiration and
burning return the gas
back to the atmosphere.
A large amount of CO2
gas is locked up within
clams, oysters, and shells
too.
S.S.Hong ; SNU 05-09-18
The CARBON-SILCATE cycle = Thermostat
Together with the BIOLOGICAL cycle the CARBON-SILICATE one regulates the
amount of atmospheric CO2 and thus determines magnitude of greenhouse effect.
The cycle depends on TEMPERATURE, since WEATHERING becomes inefficient at
low temperature.
A long SPELL of COLD increases ice coverage on Earth. Lack of liquid water on
Earth tends to stop weathering, hence it would increase atmospheric CO2 , which in
turn raises up the temperature.
 THE CARBON-SILICATE CYCLE ACTS LIKE A THERMOSTAT !
3) THE MOIST GREENHOUSE EFFECT
The CARBON-SILICATE cycle rests on the AVAILABILITY of LIQUID water.
OUTGASSING under MOIST EVIRONMENTS :
Injection of CO2 gas into atmosphere
 warming of the atmosphere via greenhouse
 acceleration of H2O evaporation
 cut off the carbonate formation process

RUNAWAY HEATING OF ATMOSPHERE !
S.S.Hong ; SNU 05-09-18
Venus had water early in the solar system history : MOIST GREENHOUSE.
Subsequent UV PHOTOLYSIS splits H2O into O and H2 ; the lightest H2 gas quickly
evaporates from the atmosphere.
Moist Greenhouse starts at 340K (67OC), which corresponds to 0.95 AU for the
present solar luminosity.
REVISION OF THE CONTINUOUSLY HABITABLE ZONE 0.95 ~ 1.13 AU
Mankind has only another billion years before the Earth becomes uninhabitable.
4) IRREVERSIBLE GLACIATION
albedo
ocean 0.04
rocks
0.15
cloud
0.52
ice
0.70
White Catastrophe !
S.S.Hong ; SNU 05-09-18
Irreversible Glaciation imposes another constraint upon the outer boundary of
the Habitable Zone.
Actual point of the irreversible glaciation depends on the roles of many
warming agents: warming by carbon-silicate cycle reaches a limit when CO2
cloud forms, since it has high albedo.
This places position of the Irreversible Glaciation at 1.67AU today. But, the
plate tectonics has an ultimate power.
PLATE TECTONICS  INTERNAL HEAT CONTENT  PLANET MASS
‘Giant Impact’
SSH ADDS GIANT IMPACT TO THE CHAIN, BECAUSE VENUS LACKS ACTIVITIES OF THE PLATE TECTONICS.
Mars is a victim of the White Catastrophe.
• small mass, low heat content, quick cooling, early death of volcanism,
no further supply of CO2 , set-in of the glaciation.
• Where is then the ice gone? Small mass, evaporation, UV photolysis, H2 lost
to space, O in oxidizing undifferentiated Fe to Fe2O3, the remaining ice buried
in the permafrost layer.
S.S.Hong ; SNU 05-09-18
7. AXIS VARIATIONS OF THE PLANETS
SPIN – ORBIT RESONANCE
rotational bulge of Earth  Sun  spin - precession
Earth orbit  planets + Moon
 orbit - precession
Spin-Orbit Resonance changes inclination angle up to 60o for Mars; 85o for Earth
without Moon. Nearby Moon actually stabilizes the spin-orbit resonance.
Consequences of the Equatorial glaciation and very warm pole may not be fatal for
the development of life. But frequent change in climate should be fatal.
S.S.Hong ; SNU 05-09-18
S.S.Hong ; SNU 05-09-18
8. BIOGENIC EVOLUTION OF ATMOSPHERES
LIFE AFFECTS LATER HABITABLITY OF
A PLANET.
Photosynthetic-bacteria generated O2 is
used up in the first 2 billion years in
oxidizing the iron in the sea water, and
later enriched the atmosphere and then
destroyed CH4 , which is a greenhouse
gas.
L(t) for Sun, volcanism, greenhouse,
carbon-silicate cycle, gas reactions,
H2O photolysis, and subsequent escape
of H2
Quenching of greenhouse action at -2
x109 yrs  Huronia Glaciation at about
the same time, 2.3 billion yrs ago.
Continuing increase in T  L(t)
Hart, H.M. 1978, Icarus 33, 23
The Evolution of the Atmosphere of the Earth
S.S.Hong ; SNU 05-09-18
Banded Iron Formations BIFS in Western Australia
Mt. Tom Price iron ore mine,
Hamersley Ranges
300 km in diameter
finely banded dark brown, ironrich layers alternating with
lighter iron-poor layers
the layers range in thickness
less than a mm to about a cm
Iron-rich bands contain the
highly insoluable iron oxides:
hematite Fe2O3, limonite Fe2O3·
3H2O, magnetite Fe3O4.
Chert, a precipitated silica,
occupies the iron-poor bands.
 appearance of free oxygen
 oxidation state of the Earth’s
ocean and atmosphere in the
Archaean Era
S.S.Hong ; SNU 05-09-18
Iron was actually consumed by bacteria flourished near thermal vents. Bacteria drifted away in
vast colonies into shallow water where they died, depositing organic-rich material. After a
while the organic material would have been recycled, leaving iron behind in highly in-soluable
oxide form.
IN SUMMARY
Habitable Zone
Glaciation
Major Cause and Epoch______
0.71 ~ 1.42 AU
1.67 AU
present solar luminosity
0.56 ~ 1.13 AU
1.35 AU
onset of H-ignition, CO2 build-up
0.95 ~ 1.13 AU
Moist Greenhouse
0.95 ~ 1.01 AU
Snowball Earth / precession
 Quenching of GH Gas
The CHZ extends over 0.06 AU from 0.95 to 1.01 AU.
The expectancy period of the Earth life is less than one billion years !
How many planets can we expect to have in such a narrow CHZ
around the right kind of central star ?
S.S.Hong ; SNU 05-09-18
9. NUMBER OF HABITABLE PLANETS
1) DRAKE’s FORMULA
N = NHP fL fI fC L/LS, where NHP = NS fP nE
N
= number of communicating extraterrestrial civilizations
NHP = number of habitable planets in the Galaxy
NS -- number of stars in the Galaxy that are suitable for life
fP
-- fraction of such stars that have planets
nE -- number of Earth-like planets orbiting in HZ for each star
fL fI fC = fraction of planets on which life develops, evolves into
intelligent being, and engages in radio communication
L
= life time of communicating societies
LS
= time-span over which Earth-like planets and their parent stars
have formed in the Galaxy
L/LS = probability of detecting a communicating society
S.S.Hong ; SNU 05-09-18
2) BEHIND THE DRAKE’s FORMULA
Project OZMA by Frank Drake (1960)
1950s G. Cocconi, P. Morrison, I.S. Shklovskii
possibility of interstellar radio communication
1960
Green Bank 25m Telescope
6 hours/ day monitoring of 2 G stars,  Ceti &  Eri
1961
Green Bank Conference organized by F. Drake
Parameterize one’s own ignorance into factors !
N = NHP fL fI fC L / LS
NHP = NS fP nE  astronomy
fL fI fC L  biochemistry, evolution, engineering, civilization
LS  astronomy
S.S.Hong ; SNU 05-09-18
3) ESTIMATES OF THE NUMBER, NHP
Total number of stars in the Galaxy
6.4 x 1010 M_sun / 0.4 M_sun  1.6 x1011 stars
G type  0.1 ; Metal Rich Pop I  0.6 ; Exclusion of Multi Sys  0.3
1.6 x1011 stars x 0.1 x 0.6 x 0.3  2.9 x 109 stars
An Adequate Supply of Water and Carbon
limit to the inner part of cluster  0.5 ; hence, NS  1.4 x 109 stars
Accretion Disks Around the Ns Stars  Solar Nebula ; fP  1.0
nE = [ 0.06 AU / 5.2 AU ] x 4 terrestrial planets x 0.06 = 0.003
migration-safe factor 
NHP = 4 x 106 stars in the Galaxy, i.e.
one in every 40,000 stars !
Trilling, D.E. et al. 1998, ApJ 500, 428 : Orbital Evolution and Migration of Giant Planets: Modeling Exrasolar Planets
Del Popolo, A., Gambera, M., Ercan, N. 2001, MNRAS 325, 1402 : Migration of Giant Planets in Planetesimal Discs
S.S.Hong ; SNU 05-09-18
4) COMPARISON OF THE NHP ESTIMATES
A wide range of uncertainty suggests a tremendous difficulty
involved in making an estimation of NHP.
The number 4 x 106 still seems to be an optimistic estimate, if giant
Moon is necessary to make Earth suitable for life.
The same number could well be a pessimistic estimate, if migration
of Jovian planets is not so common a phenomenon in reality.
Recent progress in theory of planet formation and discovery of exoplanets has refined fuzzy parameters sharper and sharper.
S.S.Hong ; SNU 05-09-18
10. DISCUSSION
Better understanding is required on the long range evolution
of planet atmosphere, gas dynamics and thermodynamics of
accretion disk, and migration of proto-Jovian planets.
Being biased with terrestrial life, we are in a danger of
blindly exercising human chauvinism.
Even so, Earth-like planets turn out to be very rare, one in
every 40,000.
As human beings, we are an extremely lucky product of the
cosmic evolution over the last 14 billion years.
The TPF Project of NASA is expected to pin-down some of
the major uncertainties involved in the NHP estimation.
Mother Earth is a Beautiful Place!
In recent years we are witnessing enormous progress in IT, whose
‘muscle’ may be combined with that of brain science. If transhumans are populous in exo-planetary systems, Drake’s formula
may lose its predicting power.
S.S.Hong ; SNU 05-09-18
SNU, 05-06-01
PLANETS SUITABLE FOR LIFE
SNU, 05-06-01
THE CONCLUSION
Mother Earth is a Beautiful Place !
Underneath the beauty resides turmoil of the plate tectonics, which
turns out to be the motor driving the evolution of life.
As long as competing factors of the turmoil find a balance, our mother
Earth reaches another vantage point towards the OMEGA.
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