Planet

A planet is a large object in space that orbits, or moves around, a star. In our solar-system, the star is the sun, and there are eight planets that travel around it. These planets are, in order from the Sun: mercury, venus, earth, mars, jupiter, saturn, uranus, and neptune. Each planet takes a different amount of time to complete one orbit around the Sun, which is called a year.

To be called a planet, an object must meet three main rules: it must orbit a star, it must be large enough for gravity to make it round, and it must have cleared its path of other objects. These rules were set by the International Astronomical Union (IAU) in 2006. Because of these rules, pluto is no longer called a planet but a dwarf planet, since it shares its orbit with other small objects.

Planets can be divided into two main types: rocky planets and gas giants. The four rocky planets—Mercury, Venus, Earth, and Mars—are smaller, have solid surfaces, and are closer to the Sun. The gas giants—Jupiter, Saturn, Uranus, and Neptune—are much larger and mostly made of gases like hydrogen and helium. These outer planets often have many moons and large systems of rings made of ice, dust, and rock.

Planets form from clouds of gas and dust around young stars. Over millions of years, particles stick together to create larger and larger bodies. gravity pulls them into round shapes, and their orbits become stable. This process is called planet formation and is part of how a solar system develops.

Earth is the only known planet with life, as it has the right balance of temperature, water, and air. However, scientists continue to search for signs of life on other planets or their moons. Telescopes and space probes help us study planets both in our Solar System and far beyond. Planets found around other stars are called exoplanets. Thousands of exoplanets have been discovered, showing that planets are common in the universe.

Planets have been studied for thousands of years. Ancient astronomers could see five of them—Mercury, Venus, Mars, Jupiter, and Saturn—with the naked eye. Today, modern technology allows scientists to learn more about what planets are made of, how they move, and whether some could support life. Understanding planets helps us learn more about the universe and our own place within it.