Earth mass

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Earth mass (M, where ⊕ is the symbol for planet Earth) is the unit of mass equal to that of Earth. 1 M = (5.97219±0.0006)×1024 kg .[1][2] Earth mass is often used to represent masses of rocky terrestrial planets.

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

One Earth mass can be converted to related units:

History of measurement[edit]

Modern methods of determining the mass of the earth involve calculating the gravitational coefficient of the Earth and dividing by the Newtonian constant of gravitation

 M_\oplus =\frac{ GM_\oplus}{ G }.

The GM product is determined using laser ranging data from earth orbiting satellites.[6]

Earlier attempts[when?] to determine Earth's mass involved measuring G directly using the Cavendish experiment, and solving for M from combining the two equations

F = ma and F = G\frac{mM_\oplus}{r^2}

using earth's gravity, g as the acceleration and combining the equations gives

mg = G\frac{mM_\oplus}{r^2}.

Solving for M gives the relationship

M_\oplus = \frac{gr^2}{G}

With this method, the values for Earth's surface gravity, radius, and G were measured empirically.

Even earlier attempts[when?] to "weigh" the earth involved estimating the mean density of the earth and its volume.

 M_\oplus = \rho V

Variation[edit]

Earth's mass is constantly changing due to many contributors. Currently, the mechanisms responsible for the loss of mass exceed the mechanisms associated with mass gain. A number of factors are involved, but can be classified into two categories; net transfer of matter, and mass which is gained or lost through the absorption or release of energy due to the Mass–energy equivalence principle. Several examples are provided:

Net gains[edit]

In-falling material
Cosmic dust, meteors, comets, etc. are the most significant contributor to Earth's increase in mass. The sum of material is estimated to be 37000–78000 tons annually[7][8]
Solar energy conversion (minuscule)
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.[citation needed]
Artificial photosynthesis (minuscule)
Can also theoretically add mass, assumed to be negligible but added for sake of completeness.[citation needed]
Heat conversion (probably minuscule)
Some outbound radiation is absorbed within the atmosphere by photosynthetic bacteria and archaea, including from chlorophyll f, which bind the energy into matter in the form of chemical bonds.[citation needed]

Net losses[edit]

Atmospheric escape of gases.
About 3 kg/s of hydrogen or 95,000 tons per year[9] and 1,600 tons of helium per year[10] are lost through atmospheric escape.
Spacecraft on escape trajectories
Spacecraft that are on an escape trajectories represent an average mass loss of about 1 ton every few years. That mass would be recovered if the spacecraft were to return to the Earth.
Human energy use
Human activities conversely reduce Earth's mass, by liberation of heat that is later radiated into space; solar photovoltaics 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 almost entirely lost to space.[11]
Additional human impact by induced nuclear fission
Nuclear fission, both for civilian and military purposes, greatly speeds up natural process of radiodecay. Some 59,000 tons of uranium was supplied by mines in 2013,.[12] The mass of the uranium is reduced as it is converted to energy during the fission reaction. Also, the growing spent fuel stockpiles and environmental releases continues to produce heat (and therefore mass) largely lost to space.[citation needed]
Earth's dynamo
As Earth despins, it loses energy, some 16 tons of mass per year.[10] 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.[citation needed]
Natural processes
Events including earthquakes and volcanoes can release energy as well as hydrogen, which may be lost as heat or atmospheric escape.[citation needed]
Radiation
From radioisotopes either naturally or through human induced reactions such as nuclear fusion or nuclear fission.[citation needed]
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.[citation needed]
Venting of gases from human spaceflight
Especially methane, hydrogen, and water, from manned satellites. Through the Sabatier reaction, exhaled carbon dioxide on manned missions in space is converted into methane (CH4) and then vented into the thermosphere,[13][14] where energetic solar rays splice that methane into hydrogen and carbon. Given a rough average daily CO2 production of a single astronaut is 1 kg/day[15] and that hydrogen would make up a quarter of the mass of CH4 (4/16),[16] mass amounts on the order of about 1 ton per year could be vented into space with current human occupation. That hydrogen could be lost through the Jeans escape mechanism.

See also[edit]

References[edit]

  1. ^ "Solar System Exploration: Earth: Facts & Figures". NASA. 13 Dec 2012. Retrieved 2012-01-22. 
  2. ^ a b The Astronomical Almanac for the Year 2014. St. Lois, MO 63197: U.S. Government Printing Office. 2014. p. K7. ISBN 978-0-7077-41420. Retrieved 5 February 2016. 
  3. ^ "Solar System Exploration: Neptune: Facts & Figures". NASA. 5 Jan 2009. Retrieved 2009-09-20. 
  4. ^ "Solar System Exploration: Saturn: Facts & Figures". NASA. 28 Jul 2009. Retrieved 2009-09-20. 
  5. ^ Williams, Dr. David R. (2 November 2007). "Jupiter Fact Sheet". NASA. Retrieved 2009-07-16. 
  6. ^ Ries, J.C.; Eanes, R.J.; Shum, C.K.; Watkins, M.M. (20 March 1992). "Progress in the determination of the gravitational coefficient of the Earth". Geophysical Research Letters 19 (6). doi:10.1029/92GL00259. Retrieved 5 February 2016. 
  7. ^ "Spacecraft Measurements of the Cosmic Dust Flux", Herbert A. Zook. doi:10.1007/978-1-4419-8694-8_5
  8. ^ Carter, Lynn. "How many meteorites hit Earth each year?". Ask an Astronomer. The Curious Team, Cornell University. Retrieved 6 February 2016. 
  9. ^ https://www.sfsite.com/fsf/2013/pmpd1301.htm
  10. ^ a b http://scitechdaily.com/earth-loses-50000-tonnes-of-mass-every-year/
  11. ^ http://www.resilience.org/stories/2012-02-16/world-energy-consumption-beyond-500-exajoules
  12. ^ http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Uranium-Resources/Uranium-Markets/
  13. ^ http://science.nasa.gov/science-news/science-at-nasa/2000/ast13nov_1/
  14. ^ http://www.nasa.gov/pdf/146558main_RecyclingEDA(final)%204_10_06.pdf
  15. ^ Sulzman, F.M.; Genin, A.M. (1994). Space, Biology, and Medicine, vol. II: Life Support and Habitability. American Institute of Aeronautics and Astronautics
  16. ^ http://www.convertunits.com/molarmass/CH4