Solar System & Planetary Science

The Solar System formed approximately 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud, centered around the Sun (a G-type main-sequence star). In 2006, the International Astronomical Union (IAU) formally defined a planet as a celestial body that orbits the Sun, has sufficient mass for hydrostatic equilibrium, and has cleared the neighborhood around its orbit, reclassifying Pluto as a dwarf planet alongside Eris, Haumea, Makemake, and Ceres. The terrestrial inner planets (Mercury, Venus, Earth, Mars) are separated from the outer gas and ice giants (Jupiter, Saturn, Uranus, Neptune) by the main Asteroid Belt. Beyond Neptune lies the Kuiper Belt and the distant spherical Oort Cloud.