The Terrestrial Planets, Part I
Mercury and Venus
MERCURYThe Winged Messenger
Physical Data
Diameter: 4,864 km (0.382 Dearth)
Mass: 3.33x1026 g (0.0558 Mearth) Density: 5.50 g/cm3
Rotation Period: 58.65 days Tilt of Axis: 0o
Surface Temperature: 700 K (day side) . 100 K (dark side)
Physical Data
Orbital Semi-Major Axis: 0.387 AU
Perihelion Distance: 0.308 AU
Aphelion Distance: 0.467 AU Orbital Period : 87.97 days (0.241 years) Orbital Inclination: 7.00o
Orbital Eccentricity: 0.206 Surface Gravity: 0.38 Earth gravity
Physical Data
Maximum Elongation: 28o (aphelion)
18o (perihelion) . 23o (average)
Satellites: None Magnetic Field: 1% strength of Earth’s
Mercury Apparitions At western elongation, Mercury is visible in
the morning before dawn (“morning star”). At eastern elongation, Mercury is visible in
the evening after sunset (“evening star”). Mercury appears to change in size, and has
phases like the Moon.
Mercury’s 3:2 Resonance
Once thought to be synchronous
Mercury rotates 3 times for every two orbits
One Mercury “day” lasts two Mercurian years!
Mercury’s Interior
Mercury is the most iron-rich planet in the solar system.
Of all the planets, Mercury has the largest core relative to its overall volume (42%, 16% for Earth)
Mercury’s Magnetic Field
1% Earth’s Magnetic Field
SUN
Mercury’s Surface
Mercury appears very Moon-like
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Mercury’s Surface
Craters
Mercury’s Surface
Lobate Scarps
Mercury’s Surface
Caloris Basin - 1300 km diameter crater
Mercury’s Surface
“Weird” (or Jumbled) Terrain
Polar caps?
Other Topics:
Precession of perihelion
Radar measurements of Mercury’s rotation
VENUSThe Goddess of Love
Physical Data
Diameter: 12,104 km (0.951 Dearth)
Mass: 4.87x1027 g (0.815 Mearth) Density: 5.30 g/cm3
Rotation Period: 243 days Tilt of Axis: 177.4o (retrograde) Suface Temperature: 750 K
Physical Data
Orbital semi-major axis: 0.723 AU Orbital period: 224.70 days (0.615 years) Orbital inclination: 3.39o
Orbital Eccentricity: 0.007 Maximun Elongation: 48o
Surface Gravity: 0.90 Earth gravity
Physical Data
Satellites: None Magnetic Field: No
Surface Pressure: 90 times Earth’s!
Venus Apparitions At western elongation, Venus is visible in
the morning before dawn (“morning star”). At eastern elongation, Venus is visible in
the evening after sunset (“evening star”). Venus appears to change in size, and has
phases like the Moon
Clouds of Venus
Clouds whiz aroud Venus at 300 km/hr.
At this speed, a cloud can circle Venus in only four days.
Clouds are composed of mostly sulfuric acid and water.
The Atmosphere of Venus
96.5% Carbon Dioxide 3% Nitrogen Traces of Other Gases:
0.019% Sulfur Dioxide
0.01% Water Vapor
0.007% Argon
Hydrochloric acid, Hydroflouric acid Atmospheric Pressure 90x Earth’s
Venus’ Atmosphere
Clouds contain sulfuric acid and water
Cloud tops appear yellow from sulfur dust
Temperature reaches a maximum at the surface of about 750 K (900o F)
15 km
45 km
60 km
75 km
Top of Clouds
30 km
Upper Cloud Deck
Droplets of Sulfuric Acid & Water
Lower Cloud Deck
Sulfuric Acid& Water and Sulfur Crystals
Haze Layer
Clouds T hin Out
Clear, Hot Atmosphere
0 km
Temperature
105 km
200 K 400 K 600 K 800 K0 K
Altitude
Why is Venus So Hot?
Venus’ Interior
Core - 12% total volume of planet
Molten core?
Thin crust, with continent sized features.
CORE( iron-nickel )
MANTLE( olivine )
CRUST( silicates)
6052 km
3616 km
Venus
Soviet Venera Missions
First Surface Photographs, 1970
Photo from Venera 13
The Magellan Mission
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Magellan Surface Imagery
Suface Features:
Impact Craters
Lava Flows
Volcanic Calderas
Volcanoes Peculiar to Venus:
Coronae, Pancake . Domes, Ticks, Graph Paper Regions
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Venus’ Surface
Graph Paper Regions
Venus’ Surface
“The Tick”
Venus’ Surface
Coronae
Venus’ Surface
Pancake Domes