Earth

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, modern Earth is the homeworld of humans, who have been spread through the galaxy by alien races.

Physical Characteristics

In versus debates, the physical characteristics of fictional inhabited planets are usually assumed to be close to those of Earth, 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

• 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"