Earth

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Mostly Harmless

Earth (aka Terra) is the third planet orbiting the Sun, an average yellow-dwarf star near the outer rim of the Milky Way galaxy, and is the only known planet that supports life. It has a single, very large natural satellite referred to as "the Moon".

Earth figures prominently as the homeworld of the human species in a great number of science-fiction stories, shows, movies, and books.

Earth in Science Fiction

In Star Trek, Earth is the capital of the United Federation of Planets and the center of most of the Federation's research and manufacturing facilities, especially those related to Starfleet. Despite Earth's importance to the Federation, the system is frequently left virtually undefended.

In Babylon 5, Earth is the capital of the Earth Alliance. The planet has an orbital defense system consisting of satellites armed with missiles and particle beams.

In Stargate, humans from Earth have been transplanted throughout the galaxy by alien races.

In Warhammer 40,000, Earth is known as Holy Terra and is the Capital of the Imperium of Man, with most of it's surface being covered by various cities. The most important structure is the Imperial Palace, home of the Emperor.

Physical Characteristics

In versus debates, the physical characteristics of fictional inhabited planets are usually assumed to be close to those of Earth[1], unless otherwise indicated in the story.

  • Radius (volumetric mean) = 6371.0 km
    • Equatorial = 6378.1 km
    • Polar = 6356.8 km
    • Crust depth = 25 km (varies)
    • Mantle thickness = 2860 km
    • Core = 3480 km
  • Mass = 5.9736E24 kg
    • Atmosphere = 5.1E18 kg
    • Hydrosphere = 1.4E21 kg
    • Crust = 3.4E22 kg
    • Mantle = 4.0E24 kg
    • Core = 1.9E24 kg
  • Distance from the Sun = 1.4960E11 m
  • Distance from the Moon = 3.8440E8 m
  • Escape velocity = 11.186 km/s
  • Bond albedo = 0.306
  • Surface temperature = 288 K
  • Gravitational binding energy = 2.5E32 J
  • Moment of inertia = 8.02E37 kg m²
  • Density = 5514.8 kg/m³
    • Atmosphere (surface) = 1.217 kg/m³
    • Crust = 2700 kg/m³
    • Mantle = 4500 kg/m³
    • Core = 1.1E4 kg/m³

Notes and References

  1. The average parameters of the core, mantle, and crust, as well as the gravitational binding energy, are based on the isotropic PREM model of Dziewonski and Anderson.
  • Dziewonski, A.M. and D.L. Anderson. Preliminary Reference Earth Model (PREM), Phys. Earth Planet. Inter. 25, 297-356, 1981.
  • Williams, David R. "Earth Fact Sheet"
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