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Big bang
Nuclear fusion in stars
Supernova nucleosynthesis
Planetary formation
Current Solar System
4. Current Solar System
Current Solar System
• Oort cloud is a hypothetical
spherical cloud. No direct
observations.
• 100 000AU; defines
gravitational boundary of
solar system
• Source of long-period
Comets
Nearest Star (Proxima Centuri)
at 4.2 light year = 1.3 pc = 2.6x105 AU
• Terrestrial (or inner rocky) planets: Mercury, Venus, Earth, Mars
• Asteroid belt: Rocky objects. Some asteroids around the outer
edge may have ice deep inside the bodies.
• Gas Giant Planets: Jupiter, Saturn, Uranus, Neptune
• Trans-Neptunian Objects
– Pluto is no longer defined as a planet.
– Edgeworth-Kuiper Belt Objects: Icy bodies, located beyond the planets
extending from the orbit of Neptune (at 30 AU) to approximately 55 AU
from the Sun
– Scattered Disk: Icy bodies: These objects have eccentric orbits, and
perihelia greater than 30 AU. (e.g. Sedna)
– Oort cloud: nearly spherical swarm of comets, originally formed in outer
solar system.
Terrestrial
planets
Gas
planets
Dwarf
planets
Diameter
Mass
Semi-major
axis
Rotational
period
Number of
satellite
Ring
Atmosp
here
Mercury
0.38
0.06
0.39
59
0
no
No
substantial
Venus
0.95
0.82
0.72
-243
0
no
CO2, N2
Earth
1
1
1
1
1
no
N2, O2
Mars
0.53
0.11
1.52
1.03
2
no
CO2, N2
Jupiter
11.2
318
5.20
0.41
>63
yes
H2, He
Saturn
9.45
95
9.54
0.43
>60
yes
H2, He
Neptune
4.01
14.6
19.22
-0.72
27
yes
H2, He
Uranus
3.88
17.2
30.06
0.67
13
yes
H2, He
Ceres
0.08
0.0002
2.77
0.38
0
no
-
Pluto
0.19
0.002
39.48
-6.39
3
no
No
substantial
Diameter
Mass
Semi-major
axis
Rotational
period
Sun
Terrestrial
planets
Orbital
period
Mass
density
-
Mercury
0.38
0.06
0.39
59
0.24
5.4
Venus
0.95
0.82
0.72
-243
0.62
5.3
Earth
1
1
1
1
1
5.5
Mars
0.53
0.11
1.52
1.03
1.9
3.9
Jupiter
11.2
318
5.20
0.41
12
1.3
Saturn
9.45
95
9.54
0.43
30
0.7
Uranus
4.01
14.6
19.22
-0.72
84
1.2
Neptune
3.88
17.2
30.06
0.67
165
1.7
Ceres
0.08
0.0002
2.77
0.38
4.6
2.1
Pluto
0.19
0.002
39.48
-6.39
248
2.0
Gas planets
Dwarf
planets
Mass densities of Europe and Titan are 3.0 and 1.9 g/cm3.
Why molecular abundance of terrestrial planets are significantly different?
N2 (78 %)
O2 (21 %)
CO2 (96 %)
N2 (3.5 %)
CO2 (95 %)
N2 (2.7 %)
H2 (93 %)
He (7%)
Formation of Earth Atmosphere
• The Earth is too small to retain atmospheric H & He.
H and He are the most abundant elements in the Universe, yet they are very
rare in the Earth's atmosphere, because H and He elements are small and
light, and so moves very fast at a given atmospheric temperature.
• After losing most of original H and He, the primordial atmosphere of the
Earth was built up by outgassing of the crust by volcanoes:
- Mostly H2O and CO2
- Small amounts of N2
• The primordial atmosphere had ~1000 times more CO2 than it does now.
Where did it all go?
- H2O condensed to form the oceans.
- CO2 dissolved into the oceans
and precipitated out as carbonates (limestone, 석회암).
• By contrast, N2 is chemically inactive. It can remain in the atmosphere.
• The second major constituent of the present-day atmosphere is O2. It comes
primarily from photosynthesis in plants.
• Ozone (O3) forms in stratosphere from O2 interacting with solar UV photons.
• It blocks UV photons from reaching the ground. This makes land on the ground
possible to live against the solar UV radiation.
• The presence of O2 and O3 in our atmosphere is a sign of life.
Greenhouse Effect
• The atmosphere is transparent to visible light, but mostly opaque to infrared.
• The Infrared "opacity" comes from absorption bands of H2O, CO2, CH4 and
others molecules.
- Photons are absorbed by the ground, heating it up
- The warm ground radiates infrared photons
• The atmosphere, however, is mostly opaque to infrared photons: Most of the
infrared photons emitted by the warm ground get absorbed by the atmosphere
on their way out, heating the atmosphere.
• The Greenhouse Effect is responsible for making the Earth about 30~40 K
warmer than it would be if there it had no atmosphere.
• Therefore, without the Greenhouse Effect, there would be no liquid water on
the Earth, only ice. Since life as we understand it requires liquid water, if
there was no Greenhouse Effect, the Earth would be inhospitable to life.
Atmospheric Composition (average)
Gas
Mole fraction
Nitrogen (N2)
0.78
Oxygen (O2)
0.21
Water (H2O)
0.04 to < 5x10-3; 4x10-6 -strat
Argon (Ar)
0.0093
Carbon Dioxide (CO2)
370x10-6 (date: 2000)
Neon (Ne)
18.2x10-6
Ozone (O3)
0.02x10-6 to 10x10 –6
Helium (He)
5.2x10-6
Methane (CH4)
1.7x10-6
Krypton (Kr)
1.1x10-6
Hydrogen (H2)
0.55x10-6
Nitrous Oxide (N2O)
0.32x10-6
Carbon Monoxide (CO)
0.03x10-6 to 0.3x10-6
Chlorofluorocarbons
3.0x10-9
Carbonyl Sulfide (COS)
0.1x10-9
Gas giant planets: Jupiter & Saturn
•
•
•
•
Dominant composition: Hydrogen + Helium, like the sun
Surface clouds: ammonia ice, water ice....
Deep in interior: liquid metallic hydrogen
Even deeper: rocky core of ~ 10~15 x (Earth mass)
Jupiter
• 5th planet from the Sun, at least 63 known moons. Largest
planet in the solar system.
• The planet is composed of mostly hydrogen and helium just
like the Sun.
• Colorful bands parallel to the Equator. Lot's of swirls and
spots: storms. One storm, the "Great Red Spot" is 2 times
the size of Earth, and has lasted for at least 300 years
(Galileo saw it in his telescope). It's a gigantic hurricane.
• The planet appears oblate (squashed). This is due to rapid
rotation (once every 10 hours!).
• Jupiter has very thin rings seen for the first time by the Voyager
spacecraft
• The Galilean Satellites: the 4 largest moons of Jupiter
– Ganymede: The largest moon in the Solar System, it has an old, cratered
surface.
– Callisto: Heavily cratered like Ganymede, lots of ice on the surface
– Europa: Smooth surface with narrow, dark stripes running across, few
craters. The surface seems to be fractured ice (water ice). Recent
information from the Galileo spacecraft suggests that there is world-wide
ocean of liquid water beneath the frozen surface. Life?
– Io: Erupting volcanos! The interior is molten, this is due to tidal forces.
• The other known moons are all rather small; many are captured
asteroids or comets. Some have retrograde orbits.
Io
Europa
Ganymede
Callisto
Europe (Moon of Jupiter)
Surface temperature
Surface pressure
Size
50-125 K
0.1 micro Pa
0.245 Earth radius
John, S. 1987
Saturn
• 6th planet. Saturn has a remarkably low density (<1 g/cm3).
• Like Jupiter and the Sun it is mostly composed of Hydrogen
and Helium, with an Earth-like core.
• It's most outstanding feature are its magnificent rings. The
rings are made of chunks of rock and ice. It is material that
failed to coalesce into a moon.
• Saturn has more than 60 moons. The largest of the Moons,
Titan has a thick Nitrogen atmosphere like Earth! It's possible
that there are methane lakes and a rain of organic materials
onto the surface. Life?
Titan (Moon of Saturn)
False color image of the cloud on the pole
Surface temperature
Surface pressure
Atmospheric composition
94 K
147 kPa (Earth 100 kPa)
N2
98.4 %
Titan is
- the largest moon of Saturn
- the only natural satellite known to have a dense atmosphere
- and the only object other than Earth for clear evidence of surface liquid
Based on the density of 1.9 g/cm³, the bulk composition is half water ice and half rocky material.
On January 14, 2005, the Huygens probe
landed on the surface of Titan.
The probe photographed pale hills with dark
"rivers" running down to a dark plain.
Current understanding is that the hills are
composed mainly of water ice.
Dark organic compounds, created in the
upper atmosphere by the ultraviolet radiation
of the Sun, may rain from Titan's atmosphere.
They are washed down the hills with the
methane rain and are deposited on the plains
over geological time scales.
http://saturn.jpl.nasa.gov/multimedia/flash/Titan/index.html
Ice giant planets: Uranus & Neptune
• Dominant composition:
– Water + Ammonia + Methane ices
– Only atmosphere contains H, He (in total only minor)
• Uranus:
– 25% Iron + Silicates
– 60% Methane + Water + Ammonia
– 15% Hydrogen + Helium
• Neptune:
– 20% Iron + Silicates
– 70% Methane + Water + Ammonia
– 10% Hydrogen + Helium
Uranus (Near-Infrared Images by Keck Telescope)
Neptune from Voyager 2
Terrestrial vs. gaseous planets
Surface temperature on equator
So many craters like moon
700K (day), 100K (night)
Surface temperature
Surface pressure
Atmospheric composition
735K
9.3 MPa
CO2
96.5%
N2
3.5%
SO2
0.015%
Surface temperature
Surface pressure
Atmospheric composition
180-330K (average 287K)
100 kPa
N2
78%
O2
21%
H2O
about 1%
Surface temperature
Surface pressure
Atmospheric composition
180-270 K
0.4-0.9 kPa
CO2
95.3%
N2
2.7 %