Our Cosmic Neighborhood
The Solar System is the gravitationally bound system of the Sun and the objects that orbit it, a vast cosmic structure that formed approximately 4.6 billion years ago from the collapse of a giant molecular cloud. At the center sits the Sun, a middle-aged yellow dwarf star that contains more than 99.8 percent of the total mass of the Solar System and provides the light and heat that make life possible on Earth. Orbiting the Sun are eight major planets, five officially recognized dwarf planets including Pluto, hundreds of moons, millions of asteroids, billions of comets, and countless smaller bodies of ice and rock that together constitute one of the most extensively studied and yet still deeply mysterious regions of the universe.
The planets of the Solar System divide naturally into two groups based on their composition and location. The four inner planets — Mercury, Venus, Earth, and Mars — are relatively small, rocky worlds with solid surfaces, composed primarily of silicate minerals and metals. These terrestrial planets formed in the warmer inner regions of the protoplanetary disk where only materials with high melting points could remain solid. The four outer planets — Jupiter, Saturn, Uranus, and Neptune — are massive gas and ice giants with thick atmospheres of hydrogen and helium and no well-defined solid surface. They formed in the colder outer regions where volatile compounds like water, ammonia, and methane could condense into ices that provided additional building material for planet formation.
This site explores six of the eight major planets, tracing a journey from the Sun-scorched surface of Mercury outward through the familiar landscapes of Earth, the dusty red deserts of Mars, and on to the magnificent gas giants Jupiter and Saturn. Each planet is a unique world with its own atmosphere, geology, weather systems, and history of exploration by robotic spacecraft and, in the case of Earth, by the humans who call it home. Together these worlds tell the story of how a cloud of gas and dust became the diverse and dynamic planetary system we inhabit today.