The Terrestrial Planets,
Part I
Mercury and Venus
MERCURY
The Winged Messenger
Physical Data
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Diameter: 4,864 km (0.382 Dearth)
Mass: 3.33x1026 g (0.0558 Mearth)
Density: 5.50 g/cm3
Rotation Period: 58.65 days
o
Tilt of Axis: 0
Surface Temperature: 700 K (day side)
100 K (dark side)
.
Physical Data
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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)
o
Orbital Inclination: 7.00
Orbital Eccentricity: 0.206
Surface Gravity: 0.38 Earth gravity
Physical Data
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o
Maximum Elongation: 28 (aphelion)
o
18 (perihelion)
o
23 (average)
Satellites: None
Magnetic Field: 1% strength of Earth’s
.
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Mercury Apparitions
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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
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Once thought to be
synchronous
Mercury rotates 3
times for every two
orbits
One Mercury “day”
lasts two Mercurian
years!
Mercury’s Interior
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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
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1% Earth’s Magnetic Field
SUN
Mercury’s Surface
m
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Mercury appears very
Moon-like
Mercury’s Surface
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Craters
Mercury’s Surface
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Lobate Scarps
Mercury’s Surface
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Caloris Basin - 1300 km diameter crater
Mercury’s Surface
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“Weird” (or Jumbled) Terrain
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Polar caps?
Other Topics:
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Precession of perihelion
Radar measurements of Mercury’s
rotation
VENUS
The Goddess of Love
Physical Data
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Diameter: 12,104 km (0.951 Dearth)
Mass: 4.87x1027 g (0.815 Mearth)
Density: 5.30 g/cm3
Rotation Period: 243 days
o
Tilt of Axis: 177.4 (retrograde)
Suface Temperature: 750 K
Physical Data
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Orbital semi-major axis: 0.723 AU
Orbital period: 224.70 days (0.615 years)
o
Orbital inclination: 3.39
Orbital Eccentricity: 0.007
o
Maximun Elongation: 48
Surface Gravity: 0.90 Earth gravity
Physical Data
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Satellites: None
Magnetic Field: No
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Surface Pressure: 90 times Earth’s!
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Venus Apparitions
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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
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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
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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
105 km
Venus’ Atmosphere
75 km
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Clouds contain
sulfuric acid and water
Cloud tops appear
Altitud
yellow from sulfur e
dust
Temperature reaches a
maximum at the
surface of about 750 K
o
(900 F)
Top of Clouds
Upper Cloud Deck
60 km
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Droplets of Sulfuric Acid & Water
Haze Layer
Lower Cloud Deck
45 km
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Sulfuric Acid& Water and Sulfur Crystals
Clouds T hin Out
30 km
Clear, Hot Atmosphere
15 km
0 km
0K
200 K
400 K
600 K
Temperature
800 K
Why is Venus So Hot?
Venus’ Interior
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Core - 12% total
volume of planet
Venus
CRUST
( silicates)
Molten core?
6052 km
3616 km
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Thin crust, with
continent sized
features.
CORE
( iron-nickel )
MANTLE
( olivine )
Soviet Venera Missions
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First Surface Photographs, 1970
Photo from Venera 13
The Magellan Mission
m
Magellan Surface Imagery
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Suface Features:
Impact Craters
Lava Flows
Volcanic Calderas
Volcanoes
Peculiar to Venus:
Coronae, Pancake
Domes, Ticks, Graph
Paper Regions
.
m
Venus’ Surface
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Graph Paper Regions
Venus’ Surface
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“The Tick”
Venus’ Surface
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Coronae
Venus’ Surface
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Pancake Domes