solar system

The solar system comprises 8 planets, approximately 170 natural planetary satellites (moons), and countless asteroids, meteorites, and comets.

There are eight planets in the solar system. The four inner terrestrial planets are Mercury, Venus, Earth, and Mars, all of which consist mainly of rock. The four outer planets are Jupiter, Saturn, Neptune, and Uranus, giant planets that consist mainly of either gases or ice. Pluto was considered the ninth planet until 2006, when the International Astronomical Union voted to classify Pluto as a dwarf planet instead.

The solar system is situated within the Orion-Cygnus Arm of the Milky Way Galaxy. Alpha Centauri, made up of the stars Proxima Centauri, Alpha Centauri A, and Alpha Centauri B, is the closest star system to the solar system.

Scientists have multiple theories that explain how the solar system formed. The favoured theory proposes that the solar system formed from a solar nebula, where the Sun was born out of a concentration of kinetic energy and heat at the centre, while debris rotating the nebula collided to create the planets.

Europa and Enceladus, moons of Jupiter and Saturn respectively, are ice-covered rocky objects that scientists think may harbour life in the water beneath the surface. Some geological evidence points to the possibility of microorganisms on Mars.