Plánetu

Plánetu is a celestial body that orbits a star and is massive enough for its own gravity to make it round in shape. It is not large enough to cause nuclear fusion, and it has cleared the neighborhood around its orbit. Planets are distinct from stars, which generate their own light through nuclear fusion, and from smaller bodies like asteroids and comets.

The term "planet" is derived from the ancient Greek word planetes, meaning "wanderer," as these celestial bodies appeared to move across the night sky relative to the fixed stars. Our solar system is known to contain eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. These planets are broadly categorized into two groups: the inner, terrestrial planets (Mercury, Venus, Earth, and Mars) which are primarily composed of rock and metal, and the outer, gas giants (Jupiter and Saturn) and ice giants (Uranus and Neptune) which are much larger and composed mostly of gases and ices.

The definition of a planet has evolved over time. The International Astronomical Union (IAU) established the current definition in 2006, which led to the reclassification of Pluto from a planet to a dwarf planet. This definition requires a celestial body to orbit the Sun, be massive enough to be rounded by its own gravity, and have cleared the vicinity of its orbit. The study of planets, both within our solar system and those orbiting other stars (exoplanets), is a major focus of modern astronomy. Understanding planetary formation, composition, and potential for life are key areas of scientific inquiry.