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