The ocean world that supports life
Earth
Earth is the third planet from the Sun and the only world we know of that supports life. It is the largest of the four rocky planets, and the only one with liquid water lying openly on its surface — oceans cover about 71% of it.
Its combination of liquid water, a protective atmosphere, a magnetic field and a geologically active interior makes Earth unusual among the planets we have explored. The 3D model on this page uses NASA's Blue Marble imagery and GEBCO elevation data.
Key facts
- Diameter
- 12,756 km
- Mass
- 5.97 × 10²⁴ kg
- Gravity
- 9.8 m/s²1.00 g
- Mean distance from Sun
- 1.00 AU≈ 150 million km
- Length of year
- 365.2 dEarth days or years
- Length of day
- 24.0 hSunrise to sunrise
- Mean temperature
- 15°CAt the surface
- Known moons
- 1+
- Axial tilt
- 23.4°
1 astronomical unit (AU) is Earth's average distance from the Sun, about 149.6 million km. Values follow the NASA Planetary Fact Sheet; many are averages and vary with how and where they are measured.
Physical characteristics
Earth's equatorial diameter is 12,756 km. It bulges slightly at the equator because of its rotation, making it about 43 km wider across the equator than from pole to pole.
With an average density of 5,514 kg/m³, Earth is the densest planet in the Solar System. Its surface gravity of 9.8 m/s² is the reference that 'g' is measured against when comparing other worlds.
Atmosphere and climate
The atmosphere is about 78% nitrogen and 21% oxygen, with roughly 0.9% argon and small amounts of carbon dioxide and water vapour. Much of the oxygen was produced by photosynthesising life over billions of years.
A natural greenhouse effect keeps the average surface temperature around 15°C, warm enough for liquid water. High in the stratosphere, the ozone layer absorbs most of the Sun's harmful ultraviolet radiation. Earth's seasons come from its 23.4° axial tilt, not from changes in its distance from the Sun — it is actually closest to the Sun in early January.
Composition: N₂ 78% · O₂ 21% · Ar 0.9%
Surface and interior
Moving plates
Earth's outer shell is broken into tectonic plates that move a few centimetres a year, building mountains, opening oceans and recycling crust into the mantle. Earth is the only planet known to have active plate tectonics today. Use the Deep Time slider in Ember’s Universe to watch continents drift over 540 million years.
Highs and lows
The surface ranges from Mount Everest, about 8,849 m above sea level, to the Challenger Deep in the Mariana Trench, nearly 11 km below it.
Layers within
Beneath the crust lies a hot, slowly flowing mantle of rock, then a liquid outer core of iron and nickel surrounding a solid inner core. Convection in the liquid outer core generates the magnetic field.
A magnetic shield
The magnetic field deflects most of the solar wind, protecting the atmosphere and surface. Where charged particles do get in near the poles, they light up the sky as aurorae.
Moons and rings
Earth has one natural satellite, the Moon. At 3,475 km across, it is unusually large compared with its planet. It raises the ocean tides and helps stabilise Earth's axial tilt, which keeps the climate steadier over long periods.
The Moon orbits at an average of about 384,400 km and is slowly drifting away, by roughly 3.8 cm a year. Earth has no rings.
Orbit and rotation
Earth orbits the Sun at an average of 1 astronomical unit (AU) — about 149.6 million km — a distance sunlight crosses in a little over 8 minutes. It travels at about 29.8 km/s and completes an orbit in 365.25 days, which is why calendars add a leap day every four years.
Earth rotates once relative to the stars every 23 hours 56 minutes; the 24-hour solar day is slightly longer because Earth also moves along its orbit while it spins.
Exploration and missions
We explore Earth from the ground, the oceans and, since 1957, from space. Satellites now monitor weather, climate, ice, oceans and land every day.
- 1957
Sputnik 1 · USSR
The first artificial satellite to orbit Earth.
- 1958
Explorer 1 · USA
Detected the Van Allen radiation belts trapped by Earth's magnetic field.
- 1968
Apollo 8 — 'Earthrise' · NASA
Astronauts photographed Earth rising above the Moon's horizon.
- 1972
Apollo 17 — 'The Blue Marble' · NASA
The crew captured one of the most reproduced images of the whole Earth.
- 1972–
Landsat · NASA / USGS
The longest continuous record of Earth's land surface from space.
- 1990
Voyager 1 — 'Pale Blue Dot' · NASA
Photographed Earth as a tiny speck from about 6 billion km away.
- 2000–
International Space Station · International
Continuously crewed since November 2000, observing Earth from low orbit.
Surprising facts about Earth
- Earth is the densest planet in the Solar System.
- Its days are slowly getting longer as tides drain rotational energy; fossil corals suggest a day lasted about 22 hours roughly 400 million years ago.
- Earth is not a perfect sphere — it is slightly squashed at the poles.
- It is the only planet not named after a figure from Greek or Roman mythology.
- Earth is at its closest to the Sun in January, during the Northern Hemisphere's winter.
Earth compared with its neighbours
| Property | Venus | Earth | Mars |
|---|---|---|---|
| Diameter | 12,104 km | 12,756 km | 6,792 km |
| Mass (Earth = 1) | 0.816 | 1.000 | 0.108 |
| Gravity | 0.91 g | 1.00 g | 0.38 g |
| Day | 116.8 d | 24.0 h | 24.7 h |
| Year | 224.7 d | 365.2 d | 687.0 d |
| Mean temperature | 464°C | 15°C | -65°C |
| Moons | 0 | 1 | 2 |
Keep exploring
- Venus: earth's scorching twin
- Mars: the red planet
- Jupiter: king of the planets
- BepiColombo — two orbiters bound for mercury
- Europa Clipper — searching for a habitable ocean
- Hera — a crash-scene investigator for planetary defence
- JUICE — europe's explorer of jupiter's icy moons
- Juno — peering beneath jupiter's clouds
- James Webb Space Telescope — the largest space telescope ever launched
- Lucy — a tour of jupiter's trojan asteroids
- OSIRIS-APEX — from bennu's sample to apophis
- Psyche — journey to a metal world
- Solar Orbiter — the first views of the sun's poles
- Fly to Earth in the interactive 3D solar system
- Watch Earth's continents drift through 540 million years of deep time
- Earth history: every geological period from the Cambrian to today
- All eight planets of the Solar System