Earth mass

Earth mass (M_E, where ⊕ is the symbol for planet Earth) is the unit of mass equal to that of Earth. 1 M_E = 5.97219 × 10²⁴ kg. Earth mass is often used to describe masses of rocky terrestrial planets.

The three other terrestrial planets of the Solar System—Mercury, Venus, and Mars—have masses of 0.055 M_E, 0.815 M_E, and 0.107 M_E, respectively.

One Earth mass can be converted to related units:

• 81.3 Lunar mass (M_L)
• 9.35 Mars mass (Mars has 0.107 M_E)
• 0.0583 Neptune mass (Neptune has 17.147 M_E)
• 0.0105 Saturn mass (Saturn has 95.16 M_E)
• 0.00315 Jupiter mass (M_J) (Jupiter has 317.83 M_E)
• 0.000 003 003 Solar mass (M_☉) (The Sun has 332946 M_E)

Variation

Earth's mass, like that of all bodies, is constantly changing. Currently, the loss of mass exceeds the gain. A number of factors are involved:

• Net gains:
  • Cosmic dust: meteors, dust, comets, etc. Estimated 40,000 tons annually
  • Solar energy conversion: Solar energy is converted into part of the mass of Earth by Photosynthetic pigments, so effectively the Sun is sending matter to be stored on Earth chemically, with photosynthesizing organisms and energy as the intermediaries. Over millions of years this mass is substantial, though most of it has been reconverted into heat and then lost (re-radiated) through chemical processes, either natural or man-made. Artificial photosynthesis can also add mass but is extremely small scale at present.
  • Heat conversion: Some outbound radiation is absorbed within the atmosphere by photosynthetic bacteria and archaea which bind the energy into matter.
• Net losses:
  • Atmospheric escape of gases. 3 kg/sec of hydrogen or 95,000 tons per year and 1,600 tons of helium per year. Additionally, some electrons are lost because they are even lighter than atoms.
  • Artificial satellites that are on an escape trajectory.
  • Human activities conversely reduce Earth's mass, by liberation of heat that is later radiated into space, in the case of solar photovoltaics, they generally do not add to the mass of Earth because the energy collected is merely transmitted (as electricity or heat) and subsequently radiated, which is generally not converted into chemical means to be stored on Earth. In 2010, the human world consumed 550 EJ of energy, or 6 tons of matter converted into heat, then mostly lost to space.
  • Earth's dynamo: As Earth despins, it loses energy, some 16 tons of mass per year. This loss of energy also weakens the long-term trend of strength of the magnetic field that protects the atmosphere from atmospheric escape.
  • Non photosynthesizing life forms consume energy, and radiate as heat.
  • Natural processes, including earthquakes and volcanoes, can release a massive amount of energy, which may be lost as heat or atmospheric escape.
  • Radiation from radioisotopes, either naturally or through human induced reactions such as nuclear fusion or nuclear fission.
  • As Earth loses net mass, its ability to hold on to the atmosphere is also altered, weaker gravity allows for more atmospheric escape.
  • Molecular heating of Earth, either by human induced processes including fossil fuel consumption or global warming, or by solar radiation or a combination thereof, can increase thermal motion of molecules, also allowing for increased atmospheric escape, but that depends on the exact location they are heated.

See also

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