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Mass Of The EarthEdit

Mass is a fundamental property of any planet, and for Earth it underpins everything from the force that keeps our atmosphere bound to the orbits of the Moon and artificial satellites. The mass of the Earth is a single, large number that scientists derive from the way Earth gravitation shapes the motions of bodies near it. In practice, what is measured most precisely is the gravitational parameter GM_Earth—the product of the gravitational constant G and the Earth’s mass M_Earth—because the motions of satellites and the Moon tell us how strong Earth’s gravity is, while G itself is a separate laboratory constant that is measured with a different set of experiments. The contemporary consensus places M_Earth at about 5.97 × 10^24 kilograms, with GM_Earth known even more precisely. The two quantities are connected by G, which remains the source of the largest uncertainty in the mass value.

Earth’s mass is not fixed at an exactly static value. It changes, albeit very slowly, through the ongoing influx of interplanetary dust and meteoroids that add material, and through the loss of light gases to space. The net change is tiny on human timescales but is a topic of careful accounting in geophysics and planetary science. The distribution of mass inside the planet also matters: a denser core and lighter crust produce different geophysical and gravitational signatures than a perfectly uniform ball.

Definition and context

  • Mass versus weight: Mass is the intrinsic amount of matter in a body, while weight depends on the gravitational field in which the body sits. For Earth, g at the surface is about 9.8 m/s^2 on average, but it varies with altitude and latitude due to the planet’s rotation and internal structure. The mass parameter that governs orbital motion is GM_Earth, not weight at a single surface point. See Gravitation and Earth for broader context.
  • Gravitational parameter: The Earth’s gravitational parameter μ_Earth is GM_Earth, the product of G and M_Earth. This parameter controls the trajectories of satellites, the Moon, and spacecraft. It is known very precisely from orbital dynamics and is a central datum in celestial mechanics. See Gravitational parameter and Lunar orbit for related topics.
  • Interior structure and density: Earth is not a uniform sphere. Its mean density is about 5.5 g/cm^3, and the distribution of density with depth affects the external gravity field. See Earth's interior and Mean density of the Earth for more detail.

Measurement and value

  • What is known: GM_Earth is determined very precisely from observations of how satellites and the Moon move in Earth's gravity field. The value is routinely used in spaceflight calculations and in geodesy. From GM_Earth and a laboratory value of G, scientists infer M_Earth. See Moon and LAGEOS (for examples of satellite tracking) and Gravity Recovery and Climate Experiment for practical measurement methods.
  • The role of G: G is a fundamental constant measured in laboratories on Earth. Its uncertainty is the limiting factor in the precision of M_Earth when GM_Earth is held fixed. Recent work and CODATA summaries discuss the current recommended value and its uncertainty; see CODATA and Gravitational constant for background.
  • Modern values: The contemporary best-known numbers are roughly:
    • M_Earth ≈ 5.97 × 10^24 kg
    • GM_Earth ≈ 3.986 × 10^14 m^3 s^-2 These figures are cross-checked against multiple independent methods, including orbital dynamics of artificial satellites like LAGEOS and the Moon, as well as gravity field mapping from dedicated missions such as Gravity Recovery and Climate Experiment and its follow-ons. See GRACE-FO for the modern continuation of that program.

Methods and tools of precision

  • Satellite dynamics: By tracking the precise motion of satellites in near-Earth space, scientists deduce the strength and shape of Earth’s gravity field, which yields GM_Earth with very high precision. See Lageos and Satellite geodesy for related topics.
  • Lunar laser ranging: The distance to the Moon, measured very precisely with laser pulses, constrains the Earth–Moon gravitational system and helps fix μ_Earth with strong confidence. See Lunar Laser Ranging.
  • Gravity field missions: Dedicated missions map how mass is distributed inside Earth, and how the external gravity field changes over time. The GRACE missions have consistently contributed to updates on GM_Earth and the understanding of mass redistribution due to hydrology, ice, and oceans. See Gravity Recovery and Climate Experiment and Gravity Recovery and Climate Experiment.
  • Laboratory measurements of G: Laboratory experiments determine the value of the gravitational constant G, which in turn converts GM_Earth into M_Earth. Because G is harder to measure with extreme precision than orbital dynamics are, M_Earth inherits some of that uncertainty. See Gravitational constant.

Mass change and processes

  • Accretion of extraterrestrial material: The Earth continually accretes dust and small meteorites from space, adding material at a cumulative, small but nonzero rate. The magnitude is frequently estimated in the tens of thousands of metric tons per year.
  • Loss to space: The Earth also loses some atmospheric gases to space, particularly light species such as hydrogen and helium, at a very slow rate.
  • Net effect: The net change in mass from these processes is small on human time scales, but it is a parameter of interest for long-term geophysical and planetary evolution studies. The exact rate remains an area where ongoing measurements and modelling improve the precision.

Significance in theory and practice

  • Orbital dynamics: The Earth’s mass sets the scale for gravitational interactions in the near-Earth environment, fundamentally shaping the orbits of the Moon and artificial satellites. This is why accurate knowledge of GM_Earth is essential for mission planning and navigation. See Orbital mechanics and Moon for broader context.
  • Atmosphere and hydrosphere: The gravitational binding force, which depends on mass, governs the retention of the atmosphere and the behavior of oceans and weather systems. See Atmosphere and Hydrosphere for related topics.
  • Geophysical interpretation: Understanding mass distribution informs models of the planet’s interior and its evolution. See Earth's interior and Geophysics for background.
  • Historical development: Early scientists inferred Earth’s mass from observed motions and universal gravitation, leading to the modern practice of combining dynamical measurements with laboratory constants. See History of science and Newtonian gravity for historical context.

See also