Earth, our home, is the third planet from the sun. It’s the only planet known to have an atmosphere containing free oxygen, oceans of water on its surface and, of course, life.
Planet Earth: Facts About Its Orbit, Atmosphere & Size
Earth is the fifth largest of the planets in the solar system. It’s smaller than the four gas giants —Jupiter, Saturn, Uranus and Neptune — but larger than the three other rocky planets, Mercury, Mars and Venus.
Earth has a diameter of roughly 8,000 miles (13,000 kilometers) and is round because gravity pulls matter into a ball. But, it’s not perfectly round. Earth is really an “oblate spheroid,” because its spin causes it to be squashed at its poles and swollen at the equator.
Water covers roughly 71 percent of Earth’s surface, and most of that is in the oceans. About a fifth of Earth’s atmosphere consists of oxygen, produced by plants. While scientists have been studying our planet for centuries, much has been learned in recent decades by studying pictures of Earth from space.
While Earth orbits the sun, the planet is simultaneously spinning on an imaginary line called an axis that runs from the North Pole to the South Pole. It takes Earth 23.934 hours to complete a rotation on its axis and 365.26 days to complete an orbit around the sun.
Earth’s axis of rotation is tilted in relation to the ecliptic plane, an imaginary surface through the planet’s orbit around the sun. This means the Northern and Southern hemispheres will sometimes point toward or away from the sun depending on the time of year, and this changes the amount of light the hemispheres receive, resulting in the seasons.
Earth’s orbit is not a perfect circle, but rather an oval-shaped ellipse, similar to the orbits of all the other planets. Our planet is a bit closer to the sun in early January and farther away in July, although this variation has a much smaller effect than the heating and cooling caused by the tilt of Earth’s axis. Earth happens to lie within the so-called “Goldilocks zone” around the sun, where temperatures are just right to maintain liquid water on our planet’s surface.
Statistics about Earth’s orbit, according to NASA:
- Average distance from the sun: 92,956,050 miles (149,598,262 km)
- Perihelion (closest approach to the sun): 91,402,640 miles (147,098,291 km)
- Aphelion (farthest distance from the sun): 94,509,460 miles (152,098,233 km)
- Length of solar day (single rotation on its axis): 23.934 hours
- Length of year (single revolution around the sun): 365.26 days
- Equatorial inclination to orbit: 23.4393 degrees
Earth’s formation and evolution
Scientists think Earth was formed at roughly the same time as the sun and other planets some 4.6 billion years ago, when the solar system coalesced from a giant, rotating cloud of gas and dust known as the solar nebula. As the nebula collapsed because of its gravity, it spun faster and flattened into a disk. Most of the material was pulled toward the center to form the sun.
Other particles within the disk collided and stuck together to form ever-larger bodies, including Earth. Scientists think Earth started off as a waterless mass of rock.
“It was thought that because of these asteroids and comets flying around colliding with Earth, conditions on early Earth may have been hellish,” Simone Marchi, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, previously told Space.com. But in recent years, new analyses of minerals trapped within ancient microscopic crystals suggests that there was liquid water already present on Earth during its first 500 million years, Marchi said.
Radioactive materials in the rock and increasing pressure deep within the Earth generated enough heat to melt the planet’s interior, causing some chemicals to rise to the surface and form water, while others became the gases of the atmosphere. Recent evidence suggests that Earth’s crust and oceans may have formed within about 200 million years after the planet took shape.
Earth’s core is about 4,400 miles (7,100 km) wide, slightly larger than half the Earth’s diameter and about the same size as Mars’ diameter. The outermost 1,400 miles (2,250 km) of the core are liquid, while the inner core is solid; it’s about four-fifths as big as Earth’s moon, at some 1,600 miles (2,600 km) in diameter. The core is responsible for the planet’s magnetic field, which helps to deflect harmful charged particles shot from the sun.