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Our solar system consists of our star, the Sun, and everything bound to it by gravity – the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune; dwarf planets such as Pluto; dozens of moons; and millions of asteroids, comets, and meteoroids.
The Sun is a 4.5 billion-year-old yellow dwarf star – a hot glowing ball of hydrogen and helium – at the center of our solar system. It’s about 93 million miles (150 million kilometers) from Earth and it’s our solar system’s only star.
For example, the nearest star system to ours is the triple star system of Alpha Centauri, at about 4.3 light years away. That's a more manageable number than 25 trillion miles, 40 trillion kilometers or 272,000 AU.
Defining the term planet is important, because such definitions reflect our understanding of the origins, architecture, and evolution of our solar system. Over historical time, objects categorized as planets have changed.
While Earth is only the fifth largest planet in the solar system, it is the only world in our solar system with liquid water on the surface. Just slightly larger than nearby Venus, Earth is the biggest of the four planets closest to the Sun, all of which are made of rock and metal.
Our solar system’s small bodies – asteroids, comets, and meteors – pack big surprises. These chunks of rock, ice, and metal are leftovers from the formation of our solar system 4.6 billion years ago.
Stars with two solar masses are about 10 times more common than stars with four solar masses, and so on. The most common type of star turns out to be one with about 0.25 solar
The craters themselves, which have been preserved for billions of years, provide an impact history for the Moon and other bodies in the inner solar system. If you looked in the right places on the Moon, you would find pieces of equipment, American flags, and even a camera left behind by astronauts.
Each successive generation of stars had higher amounts of the heavier chemical elements formed in the previous generation. The composition of newer stars was different from that of older stars. Our star, the sun, belongs to the generation of stars created 4.6 billion years ago.
NASA’s real-time science encyclopedia of deep space exploration. Our scientists and far-ranging robots explore the wild frontiers of our solar system.