Properties of Venus

Global Properties:

  • Radius: 95% radius of Earth
  • Mass: 82% mass of Earth
  • Average density: 95% of Earth
  • Rotation rate: 243 Earth days
  • No natural satellites
  • Noplanetary magnetic field

Orbital & Rotational Properties:

  • Third-brightest object in our sky, due to its proximity to Earth and the planet’s high reflectivity
  • As an inferior planet, Venus shows distinct phases to an Earth-bound observer.
  • Colloquially known as the “morning” or “evening” star.
  • Venus never exceeds a 47 separation from the Sun on the sky.
  • Average distance from the Sun = 108 million km = 0.72 AU
  • Comes closer to Earth than any other planet, minimum separation = 40 x 106 km
  • Orbital period = 224 Earth days
  • Venus rotates once every 243 Earth days; its axis is tilted 177 compared to Earth's 23.5.
  • Its slow and retrograde rotation is difficult to explain - possibly due to a massive collision early in Venusian history.

Atmosphere:

  • Distinctly not like Earth: 96.5%carbon dioxide, 3.5%nitrogen.
  • 90 times more massive than Earth's, very low speed surface winds, < 5 km/hr
  • Cloud layer is located 50-70 km above the surface
  • Clouds are composed of sulfuric acid droplets, NOT water vapor.
  • Measurements have been made in situ by the Soviet Venera and US Pioneer Venus spacecraft.
  • Venus has experienced a runaway-greenhouse effect - carbon dioxide traps surface infrared radiation, heating the planet several hundred degrees.

Surface Features and Geology:

  • Mean surface temperature is about 730 K (!), due to carbon dioxide greenhouse effect.
  • The surface is NOT visible from above the clouds.
  • Topography investigated using radar and soft-landing spacecraft.
  • The surface is rocky, no oceans, no bodies of water.
  • Most of the surface is classified as rolling plains (65%), and lowlands (27%); “continents” comprise just 8%.
  • No topographic evidence for plate tectonics.
  • We see many structures which appear volcanic in origin, e.g., lava domes, shield volcanoes, lava flows, and the odd-shaped coronae
  • The Soviet Venera landers photographed the surface around the spacecraft. They found that surface rocks were predominately basalt, produced by flowing lava.
  • Analysis of the radar data suggests that the Venusian surface is probably less than 1 billion years old, and has been resurfaced by extensive volcanic activity. Erosion by wind and water does not occur.

Interior:

  • No observed magnetic field, a likely consequence of Venus' slow rotation.
  • Little current data exists to constrain the interior. Probably a (partially ?) molten iron core exists, by analogy to Earth’s interior.

Exploration:

Much of our knowledge about Venus has been derived from spacecraft.

  • Mariner 2 (1962 USA) – 1st flyby of another planet, confirmed surface temperature, did not detect a planetary magnetic field
  • Venera 7 (1970 USSR) – 1st spacecraft to land on another planet
  • Venera 9 (1975 USSR) – 1st photographs of surface
  • Pioneer Venus (1978 USA) - radar-mapping orbiter, 5 atmospheric probes.
  • Magellan (1989 USA) - high-resolution radar mapping mission; has provided the best images to date.