Venus_Texbook_Part

10.2 The Geology of Venus

Learning Objectives

• Understand geological similarities and differences between Venus and Earth.

• Study the surface features and geological history of Venus through craters and volcanic activity.

• Analyze the surface conditions that make Venus inhospitable to life.

Overview of Venus

• Size and Composition: Venus is similar in size and composition to Earth, but shows significant differences in geology.

  • No plate tectonics observed on Venus.

  • The surface lacks significant erosion, leading to distinct geological features.

Spacecraft Exploration of Venus

• Almost 50 spacecraft launched to Venus; about half succeeded.

• Key Missions:

  • Mariner 2 (1962) - First successful flyby.

  • Venera 7 (1970) - First lander to operate on the surface for 23 minutes.

  • Magellan - Provided detailed radar mapping of Venus with 100-meter resolution, revealing complex surface features.

Surface Features of Venus

• Radar Mapping: Radar waves penetrate clouds to map surface topography, yielding insights into geological history.

  • 75% of surface consists of lowland lava plains, resembling basaltic ocean basins.

  • Continents: Two primary continents - Aphrodite (largest, equatorial) and Ishtar (northern highland region).

  • Craters: Counting impact craters allows age estimation; indicates surface age of 300 to 600 million years.

Craters and Volcanoes

• Craters:

  • Largest crater, Mead, is 275 km in diameter.

  • Few smaller craters suggest atmosphere protects against smaller projectiles.

• Volcanoes:

  • Volcanoes actively reshaping the surface; flows of lava destroy craters.

  • Sif Mons: Largest volcano, 500 km across, with a caldera of 40 km.

  • Unique pancake domes formed by viscous lava flow.

Tectonic Features

• Tectonic Forces: Convection currents in the mantle create geological features; leads to ridges and rift valleys.

  • Coronae: Circular features indicating subsurface volcanism stressing the surface.

Inhospitable Conditions

• High surface pressure (90 bars) and temperatures hotter than lead-melting point make Venus uninhabitable.

• Surface primarily composed of igneous rock, mainly basalts; landscape appears flat and desolate.

10.3 The Massive Atmosphere of Venus

Learning Objectives

• Discuss the atmospheric composition, structure, and greenhouse effect on Venus.

Atmospheric Composition

• Major Components:

  • Carbon Dioxide (CO2): 96%

  • Nitrogen (N2): 3.5%

  • Very dry atmosphere with little humidity.

• Atmospheric pressure on Venus is significantly higher than on Mars or Earth.

Structure of the Atmosphere

• Troposphere extends up to 50 km, with temperature variations similar to ocean depths.

• Clouds primarily composed of sulfuric acid droplets.

Surface Temperature

• Surface temperature exceeds 700 K due to strong greenhouse effect.

• CO2 traps heat, preventing infrared radiation from escaping.

Evolution of Venus's Atmosphere

• Possible transition from an Earth-like environment to extreme greenhouse conditions:

  • Increased solar output leads to water evaporation and enhanced greenhouse gases.

  • Loss of water is irreversible due to escape of hydrogen, preventing restoration of Earth-like conditions.

• Venus's current state signals potential risks of greenhouse effects on Earth.