Earth mass (M⊕, where ⊕ is the symbol for planet Earth) is the unit of mass equal to that of Earth. 1 M⊕ = 5.97219 × 1024 kg. Earth mass is often used to describe masses of rocky terrestrial planets.
One Earth mass can be converted to related units:
- 81.3 Lunar mass (ML)
- 9.35 Mars mass (Mars has 0.107 M⊕)
- 0.0583 Neptune mass (Neptune has 17.147 M⊕)
- 0.0105 Saturn mass (Saturn has 95.16 M⊕)
- 0.00315 Jupiter mass (MJ) (Jupiter has 317.83 M⊕)
- 0.000 003 003 Solar mass (M☉) (The Sun has 332946 M⊕)
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 (minuscule) can also theoretically add mass, assumed to be negligible but added for sake of completeness.
- 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.
- Net losses:
- Atmospheric escape of gases. 3 kg/s 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; 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.
- Additional human impact by induced 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, however the growing spent fuel stockpiles and environmental releases of years past continues to produce heat (and therefore mass) largely 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 as well as hydrogen, 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.
- Venting of wastes, 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, 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 and that hydrogen would make up a quarter of the mass of CH4 (4/16), substantial amounts of mass could be vented into space if human occupation is large enough. That hydrogen would almost entirely float away from earth.
- "Solar System Exploration: Earth: Facts & Figures". NASA. 13 Dec 2012. Retrieved 2012-01-22.
- "Solar System Exploration: Neptune: Facts & Figures". NASA. 5 Jan 2009. Retrieved 2009-09-20.
- "Solar System Exploration: Saturn: Facts & Figures". NASA. 28 Jul 2009. Retrieved 2009-09-20.
- Williams, Dr. David R. (2 November 2007). "Jupiter Fact Sheet". NASA. Retrieved 2009-07-16.
- "Spacecraft Measurements of the Cosmic Dust Flux", Herbert A. Zook. doi:10.1007/978-1-4419-8694-8_5
- Sulzman, F.M.; Genin, A.M. (1994). Space, Biology, and Medicine, vol. II: Life Support and Habitability. American Institute of Aeronautics and Astronautics