Earth mass

Earth mass
19th-century illustration of Archimedes' quip of "give me a lever long enough and a fulcrum on which to place it, and I will move the earth"[1]
General information
Unit systemastronomy
Unit ofmass
SymbolM🜨
Conversions
M🜨 in ...... is equal to ...
   SI base unit   (5.9722±0.0006)×1024 kg
   U.S. customary   1.3166×1025 pounds

An Earth mass (denoted as M🜨, M or ME, where 🜨 and are the astronomical symbols for Earth), is a unit of mass equal to the mass of the planet Earth. The current best estimate for the mass of Earth is M🜨 = 5.9722×1024 kg, with a relative uncertainty of 10−4.[2] It is equivalent to an average density of 5515 kg/m3. Using the nearest metric prefix, the Earth mass is approximately six ronnagrams, or 6.0 Rg.[3]

The Earth mass is a standard unit of mass in astronomy that is used to indicate the masses of other planets, including rocky terrestrial planets and exoplanets. One Solar mass is close to 333000 Earth masses. The Earth mass excludes the mass of the Moon. The mass of the Moon is about 1.2% of that of the Earth, so that the mass of the Earth–Moon system is close to 6.0457×1024 kg.

Most of the mass is accounted for by iron and oxygen (c. 32% each), magnesium and silicon (c. 15% each), calcium, aluminium and nickel (c. 1.5% each).

Precise measurement of the Earth mass is difficult, as it is equivalent to measuring the gravitational constant, which is the fundamental physical constant known with least accuracy, due to the relative weakness of the gravitational force. The mass of the Earth was first measured with any accuracy (within about 20% of the correct value) in the Schiehallion experiment in the 1770s, and within 1% of the modern value in the Cavendish experiment of 1798.

  1. ^ Attributed by Pappus of Alexandria (Synagoge [Συναγωγή] VIII, 4th century), as « Δός μοί ποῦ στῶ, καὶ κινῶ τὴν Γῆν ». Engraving from Mechanic's Magazine (cover of bound Volume II, Knight & Lacey, London, 1824).
  2. ^ The cited value is the recommended value published by the International Astronomical Union in 2009 (see 2016 "Selected Astronomical Constants" Archived 15 February 2016 at the Wayback Machine in "The Astronomical Almanac Online" (PDF). USNO/UKHO. Archived from the original on 24 December 2016. Retrieved 8 February 2016.).
  3. ^ Lawler, Daniel. "Earth now weighs six ronnagrams: New metric prefixes voted in". phys.org. Retrieved 21 November 2022.