The Solar System
The Solar System consists of the Sun and the celestial objects gravitationally bound to it, including eight planets, their moons, and countless asteroids and comets.
The Solar System formed roughly 4.6 billion years ago from the gravitational collapse of a giant molecular cloud, with the vast majority of its mass concentrated in the Sun itself.
The eight planets are divided into the smaller, rocky inner planets — Mercury, Venus, Earth, and Mars — and the larger outer gas and ice giants — Jupiter, Saturn, Uranus, and Neptune. Pluto was reclassified as a dwarf planet in 2006.
Ongoing space exploration missions continue to expand understanding of the Solar System, from Mars rovers to probes that have visited every planet and several of its moons and asteroids.