Earth Content from the guide to life, the universe and everything


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The Solar System | Mercury | Venus | Earth | Mars | Ceres | Jupiter
Saturn | Chiron | Uranus | Neptune | Pluto
The Kuiper Belt and the Oort Cloud | Quaoar | Eris | Sedna


Earth is the third planet from the Sun, and, as far as we know, where all humans live.

The Facts1

  • Mass: 5.9736×1024kg
  • Equatorial Radius: 6378.1km
  • Mean Density: 5515kg/m3
  • Length of Day: 24.0000 hours
  • Period of Revolution about Sun: 365.256 days
  • Acceleration due to Gravity: 9.81m/s2
  • Mean Orbital Velocity: 29.78km/s
  • Inclination of Axis: 23.45°
  • Mean Distance from the Sun: 1 AU

Earth's atmosphere is mainly made up of Nitrogen (78%). The other major atmospheric gas is Oxygen (21%) with very small amounts of Argon, Carbon Dioxide, Neon, Helium, Krypton and Hydrogen. Earth's weather is relatively calm by solar system standards - wind speeds vary from 0 to 100m/s (compared with Neptune's 560m/s wind speed).

As far as we know, Earth is the only planet in the solar system that supports life, although it is believed there are other candidates, such as Europa. Earth is suitable for living things2 because of its molten core, which causes a magnetic field around the Earth that protects the surface from harmful radiation and particles coming from the Sun, and because of its abundant water.

Earth is in possession of a rather large satellite, called the Moon.

See? It's Mostly Harmless.

The h2g2 Tour of the Solar System

Take the h2g2 Shuttle for your whistle-stop tour of the Solar System.

1For further information on Earth, see the rest of the Guide.2That is, living things which bear resemblance to us; there may be other types of life out there for which earth would be eminently unsuitable.

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