Space · Planets
Earth
The only planet with confirmed liquid surface water — and, by extension, the only one known to host life.
Quick facts
Type
Terrestrial
Distance from Sun
1.000 AU
149.6 million km
Diameter
12,756 km
Mass
1 Earth masses
5.97 × 10²⁴ kg
Surface gravity
9.81 m/s²
Day length
23.93 Earth hours
Year length
365.25 Earth days
1 Earth years
Mean surface temperature
−88 to 58 (15 mean) °C
Atmosphere
78% N₂, 21% O₂, 0.9% Ar
Confirmed moons
1
Naming origin
Old English ‘eorþe’ — soil/ground
What's there
Earth is the reference world. Liquid water covers 71% of the surface, an oxygen-rich atmosphere sits at one bar pressure, a magnetic field deflects most of the solar wind, and a single large moon stabilizes the planet's axial tilt — collectively the conditions that allow complex chemistry to persist over geological time. Plate tectonics recycle surface carbon into the mantle and back, a feedback loop that has kept Earth's temperature within habitable bounds for nearly four billion years.
From orbit the planet reads as blue and white — oceans and clouds — with the green and tan continents in between. Earth's day is 23 hours 56 minutes (a sidereal day; the 24-hour civil day accounts for the additional rotation needed to point back at the Sun). The axial tilt of 23.4° produces the seasons. Earth is the only planet on which the surface temperature spans both sides of water's freezing and boiling points simultaneously, allowing the hydrological cycle that shapes geology and life.
Moons
| Name | Diameter | Orbital radius | Discovered | Discoverer |
|---|---|---|---|---|
| Luna | 3475 km | 384,400 km | prehistoric | Known to all of humanity |
Naming etymology
Earth is the only solar-system planet not named for a Greek or Roman deity. The English name derives from Old English 'eorþe' (soil, ground, the world humans walk on) and Germanic 'erþō', meaning the same — a workmanlike word for the substrate underfoot, not a personification. The other languages of the world follow similar patterns: 'Terra' in Latin (and its Romance descendants), 'Gaia' in Greek (after the primordial earth goddess, used scientifically more than colloquially), '地球' (dìqiú, 'earth-globe') in Chinese. The pattern reflects that humans named Earth before recognizing it as a planet — the other planets were named because they moved against the stars, but Earth was just 'the world.'
Methodology & sources
Numerical data drawn from the NASA Planetary Fact Sheets; satellite parameters from JPL Solar System Dynamics — Physical Parameters and the JPL Satellite Discovery Circumstances table. Mission history cross-referenced against NASA's mission catalog and individual mission pages. Naming etymology from the IAU Working Group for Planetary System Nomenclature. Hero rendering is a stylized SVG composed from primary-source visual reference (NASA / JPL imagery) — no photographs are reproduced.