Earth is the only place we know of where liquid water pools on the surface - and the only place we know of with life. It sits in the Sun’s habitable zone: close enough that water doesn’t freeze solid, far enough that it doesn’t boil away.
Open the 3D Solar SystemEarth does two things at once: it spins on its axis once every 24 hours (that’s a day) and it travels around the Sun once every 365¼ days (that’s a year). The leftover quarter-day is why we add a leap day every four years.
| Diameter | 12,756 km |
| Mass | 5.970e+24 kg |
| Surface gravity | 9.8 m/s² |
| Density | 5.51 g/cm³ |
| Rotation period | 23.93 h |
| Axial tilt | 23.4° |
| Mean temperature | 15 °C |
| Temperature range | -89 °C to 57 °C |
| Geometric albedo | 0.43 |
| Known moons | 1 |
| Atmosphere | 78% N₂, 21% O₂ and 1% argon at 1 bar - the only known atmosphere whose free oxygen is continuously made by life. |
| Composition | An iron-nickel core (solid inner, molten outer), a silicate mantle, and a thin crust broken into drifting tectonic plates. |
How we know: Earthquake waves crossing the planet reveal each boundary directly - seismology gives Earth the best-known interior of any world.