Download Terrestrial Planets

Mercury
Radius:
Mass:
Surf. Gravity:
Density:
Semi-major axis
3.72 m/s2
5.43 g /cm3
59.7 x 106 km
87.97 days
Rotation Period
58.65 days
Composition:
Composition silicates dominate with Fe & Ni core
Magnetic Field:
Field Weak, but detectable
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3.28 x 1023 kg
Orbital Period
Eccentricity
Atmosphere:
Atmosphere MINOR
2440 km
0.206
Geology
Difficult to observe due to proximity to Sun; visible < 2 hrs.
Info comes from Mariner 10 (surface studies) and radar ranging
(orbital properties)
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Geology
Thin mantle surrounds a normal sized Fe/Ni core (D ~ 3500 km)
Crust & upper mantle possibly torn away by
a large impactor.
Weak magnetic field implies a partially molten
interior.
Atmosphere: very thin due to low surface gravity & intense heat
Sources of atmospheric particles: atoms from regolith and solar wind
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Terrain
Cratering:
Cratering similar to Moon in number; shallower
No extensive mare ! original surface
Level plains exist where impacts haven’t occurred
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Terrain
Scarps – extended cliffs along the surface (no plates/atmosphere)
Cause: uneven cooling of interior after surface solidified
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Terrain
Caloris Basin – large (D ~ 1400 km) impact basin
Shockwaves produced: cliff rings around impact
hilly-lineated terrain on opposite side
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Orbital Properties
Mercury experiences a 3:2 orbital resonance with the Sun
(3Prot = 2Porb)
1 Mercurian Day = 176 days
Tday = 550 °C
Tnight = -175 °C
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Orbital Properties
Point of perihelion moves around the Sun 9.5 " per century
Perihelion (20,000 yrs later)
Perihelion
Newton’s Law of Gravity cannot fully explain; Einstein’s theory of
Gravity (General Relativity) explains it fully.
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Venus
Radius:
Mass:
Surf. Gravity:
Density:
Semi-major axis
DVenus = 0.95 DEarth
MVenus = 0.82 MEarth
Closest planet to Earth
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6050 km
4.87 x 1024 kg
8.90 m/s2
5.24 g /cm3
108.2 x 106 km
Orbital Period
224.7 days
Rotation Period
243.02 days
“Earth’s Twin”
Surface Features
Difficult to observe due to thick atmosphere:
- Radar mapping (Arecibo, Mariner, Magellan)
- Surface Landers (Venera; 11 Soviet missions)
65% plains
10% continents
25% lowlands
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Surface Features
Once geologically active, majority of activity ceased 500 Myrs ago
Maat Mons (largest volcano) show lava flows from 10 Myrs ago
Recent volcanism (1970’s) seen in increased sulfur dioxide levels
in atmosphere.
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Surface Features
Cratering: fewer than other terrestrial worlds
- shallower due to lava flooding
Stress fractures along surface
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Atmosphere
Composition
Earth
Venus
N2
78%
3.5%
O2
21%
NONE
0.096%
96%
Water vapor
Sulfuric Acid
CO2
Clouds
Atmospheric pressure depends on:
- surface gravity of planet (same)
- mass of molecules (CO2 > N2)
- number of molecules (Venus has A LOT more)
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Earth = 1 atm
Venus = 90 atm
Atmosphere
At its present distance from the Sun, Venus’ surface temperature
should be 100 °C; Measured to be 480 °C
Runaway Greenhouse Effect
• Visible light (~2%) penetrates atmosphere & heats the surface
• Surface heats up and radiates IR toward space
• Large amounts of CO2 prevents IR from escaping
• IR continually heats up the surface
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Atmosphere
Why are the atmospheres of Earth and Venus so different?
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No water to wash out carbon dioxide
Orbital Properties
One of two planets that has a retrograde rotation
Rotational period is longer than its orbital period (Day > Year)
Slow rotation = weak magnetic field (0.0001 Earth’s mag. field)
Next transits: 2004 & 2012 (next transits are in 2134 & 2146)
Next mission: MErcury Surface, Space ENvironment, GEochemistry,
& Ranging (MESSENGER) spacecraft
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Mars
Radius:
Mass:
Surf. Gravity:
Density:
Semi-major axis
Orbital Period
Rotation Period
3397 km
6.39 x 1023 kg
3.72 m/s2
3.93 g /cm3
227.9 x 106 km
1.881 years
24.623 hours
Two moons: captured
asteroids
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Phobos
Deimos
Missions
NASA has sent 16 various space vehicles to study Mars:
Mariner: 3, 4, 6, 7, 8 & 9
Flyby Missions
Viking: 1 & 2
Mars Observer
Orbiters
Mars Climate Orbiter
Pathfinder
Polar Lander/Deep Space 2
2003 Mars Exploration Rover
Landers/Orbiters
Mars Express
2001 Mars Odyssey
Mars Global Surveyor
NASA Success Rate: 68%
U.S.S.R. & UK success rate: 0 for 16
Future Missions:
Missions Reconnaissance, H2O search, manned mission?
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Atmosphere
CO2 dominates (95%)
Very Thin (0.007 atm)
H2O sublimates
(solid # gas)
TDay = 30 ºC TNight = -175 ºC
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Atmosphere
High speed winds create extensive dust storms and dust devils
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Dust Devil
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Seasons
Ice caps dominated by CO2
(H2O under South Pole cap)
North
South
Mars’ inclined rotational axis (25.2º) makes for Earth-like seasons
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Surface Features
Only planet with surface features visible from Earth.
Red surface due to oxidized metals (rust)
Dust storms make for shallow craters
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Volcanoes
Largest:
Largest OLYMPUS MONS
HEIGHT: 25 km
BASE WIDTH: 600 km
CALDERA: 5400 sq. km
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Terrestrial Comparisons
Mt Everest: 8.8 km, Mauna Kea: 9 km
Length of Washington
Manhattan: 800 sq. km
Canyons
Crust fractures as a result of interior stresses
Grand Canyon
Ius Chasm
Length
365 km
600 km
Width
29 km
150 km
Depth
1.8 km
5 km
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Surface Features
VALLES MARINERIS
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Length
5000 km
Width
600 km
Depth
8 km
Evidence for Liquid Water
Sediment Deposits
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Evidence for Liquid Water
Mud Cracks
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Evidence for Liquid Water
Braided Rivers
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Evidence for Liquid Water
Water Runoff
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Evidence for Liquid Water
Dried Channels*
* 1st observed by Schiaparelli: canali = channels (not canals)
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Evidence for Life?
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Evidence for Life?
Other evidence that a Martian civilization built Earthly structures?
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Evidence for Life?
Viking 1 & 2 biologic experiments found
NO conclusive evidence of Martian life.
Fossilized microbes in meteorite ALH 84001?
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