About Solar System
The Solar System formed about 4.6 billion years ago from a cloud of gas and dust. Today it includes the Sun, eight major planets, dwarf planets, moons, asteroids, comets, rings, dust, and countless smaller objects held together by gravity.
The Sun
The Sun contains almost all of the Solar System's mass.
Learn MoreRocky Planets
Mercury, Venus, Earth, and Mars have solid surfaces.
Learn MoreGiant Planets
Jupiter and Saturn are gas giants, while Uranus and Neptune are ice giants.
Learn MoreDwarf Planets
Pluto is one of several recognized dwarf planets.
Learn MoreAsteroids
Most known asteroids are rocky or metallic bodies smaller than planets.
Learn MoreComets
Comets contain ice, dust, and rocky material from the cold outer Solar System.
Learn MoreOrbits and Gravity
Every planet follows an orbit because gravity continually bends its motion.
Learn MoreThe Heliosphere
The Sun influences a region far beyond the planets.
Learn MoreThe Sun
The Sun is a star made mostly of hydrogen and helium. Its gravity keeps planets and smaller objects in orbit, while energy from nuclear fusion provides the light and heat that reaches Earth. Even though the Sun looks enormous to us, it is only one star among hundreds of billions in the Milky Way.
Rocky Planets
The four inner planets are relatively small and dense. They are made mostly of rock and metal, but each is very different. Mercury is heavily cratered, Venus has a crushing atmosphere, Earth has oceans and life, and Mars preserves evidence of a wetter ancient past.
Giant Planets
The outer planets are much larger than the rocky worlds. Jupiter and Saturn are dominated by hydrogen and helium. Uranus and Neptune contain larger amounts of water, ammonia, and methane compounds deep inside, giving them different internal structures.
Dwarf Planets
A dwarf planet orbits the Sun and is massive enough for gravity to pull it into a nearly round shape, but it has not cleared other objects from its orbital neighborhood. Pluto, Ceres, Eris, Haumea, and Makemake are recognized examples.
Asteroids
Many asteroids orbit in the main belt between Mars and Jupiter, but others travel in different paths around the Sun. Studying them helps scientists learn about material left over from the formation of the planets.
Comets
When a comet approaches the Sun, heat causes frozen material to release gas and dust. This can create a glowing coma and long tails. A comet's tail points generally away from the Sun because of sunlight and the solar wind.
Orbits and Gravity
An orbit is not a place where gravity disappears. Instead, an orbiting object is constantly falling toward the body it circles while also moving sideways fast enough to keep missing it. Planets follow elliptical, or slightly stretched, paths around the Sun.
The Heliosphere
The solar wind carries charged particles outward from the Sun and forms a huge bubble called the heliosphere. Voyager 1 and Voyager 2 have crossed the heliopause, a boundary where the Sun's particle influence gives way to the surrounding interstellar environment.