Earth (Planet) — Facts, Moons, Atmosphere, and Exploration
Earth is the third planet from the Sun and the only known world with widespread liquid water and life. Its active geology, atmosphere, and magnetic field together create a stable environment for ecosystems.
Quick Facts
| Planet type | Terrestrial (rocky) |
|---|---|
| Mean radius | 6,371 km |
| Mass | 5.97 × 10^24 kg |
| Gravity | 9.8 m/s² |
| Average temperature | 15°C |
| Length of day | 24 hours |
| Length of year | 365 days |
| Number of moons | 1 |
| Rings | No |
| Distance from Sun (AU) | 1.00 |
What Makes Earth Unique
Earth combines moderate temperatures, stable liquid water, and complex chemistry at the surface. Plate tectonics recycles crust and helps regulate carbon over geological timescales, while a strong magnetic field reduces charged-particle impacts from the solar wind.
From a planetary science perspective, Earth is a reference point for comparing habitability elsewhere.
Atmosphere and Weather
Earth's atmosphere is mostly nitrogen and oxygen, with trace gases that influence climate. Water vapor, clouds, and ocean circulation create diverse weather patterns, from tropical storms to polar cold fronts.
Long-term climate change reflects interactions among sunlight, greenhouse gases, land surfaces, and ocean systems.
Moons and Rings
Earth has one large moon that stabilizes axial tilt and drives strong ocean tides. Earth has no planetary ring system.
Exploration Highlights
Human spaceflight began in Earth orbit, and Earth-observing satellites now track weather, climate, forests, oceans, and natural hazards. Missions to the Moon and planets are launched from Earth and return data that helps us understand both other worlds and our own.
If You Like Earth
Compare with Venus for greenhouse contrast, Mars for an ancient potentially wetter world, and Jupiter to see how giant planets differ from rocky worlds.
Is Earth an Inner or Outer Planet?
Earth is an inner planet. It is one of the four planets that orbit closest to the Sun, along with Mercury, Venus, and Mars. For a bigger comparison, see the inner vs outer planets guide.
What Type of Planet Is Earth?
Earth is a terrestrial planet, also called a rocky planet. It has a solid surface, a metal core, and a crust made mostly of silicate rock, which places it in the same broad group as Mercury, Venus, and Mars.
Earth is also the benchmark for habitability. For a practical comparison of why humans live here naturally but would need technology elsewhere, read Can Humans Live on Other Planets?.
FAQ
Is Earth exactly in the center of the habitable zone?
Not exactly. The habitable zone is a range, and Earth sits within it under current solar and atmospheric conditions.
Why does Earth have seasons?
Seasons come mainly from Earth's axial tilt, not from major distance changes from the Sun during one orbit.
Could Earth ever have rings?
A temporary ring is theoretically possible after a large impact, but Earth does not have a stable ring system today.
Is Earth an inner planet?
Yes. Earth is one of the four inner planets in the Solar System.
What type of planet is Earth?
Earth is a terrestrial planet, meaning it is a rocky world with a solid surface.
Is Earth a terrestrial planet?
Yes. Earth belongs to the terrestrial planet group together with Mercury, Venus, and Mars.