The cloud that formed our solar system may have started to collapse after a shockwave from a nearby exploding star.
Planets grew from a spinning disk of gas and dust around the young Sun, as clumps smashed into one another and formed larger and larger objects.
The Sun is at the center of our solar system, and sunlight takes about eight minutes to reach Earth. About 1.3 million Earths could fit inside the Sun, and it holds 99.8 percent of all the mass in our solar system.
Mercury, Venus, Earth and Mars are the four rocky inner planets, and Mercury is the smallest planet and the planet closest to the Sun, while Venus is the second planet from the Sun and Earth is the third planet from the Sun.
There is a belt of asteroids, which are rocky space rocks, between Mars and Jupiter, and more than a million asteroids orbit the Sun in this main belt, while the asteroid belt is made of bits and pieces left over from the early solar system that never came together into a planet.
Jupiter is the largest planet in our solar system, and it is a gas giant, so it does not have a true solid surface. It is more than twice as massive as all the other planets combined. Early in the solar system, the gravity of newly formed Jupiter stopped planet-building in the asteroid belt, so only small rocky bodies were left there.
Astronomers think Neptune migrated early in the solar system's history, and that this shifted Pluto and other Kuiper Belt objects into the orbits they have now.
The Kuiper Belt's inner edge begins at Neptune's orbit, about 30 AU from the Sun, where one astronomical unit (AU) is the distance from the Sun to Earth, about 93 million miles (150 million kilometers).
Pluto's oval-shaped orbit takes it from about 30 AU to about 49 AU away from the Sun, and astronomers estimate that all the material in the Kuiper Belt adds up to far less than Earth, no more than about 10 percent of Earth's mass.
The Sun formed about 4.6 billion years ago from a giant spinning cloud of gas and dust. In the 1950s Clair Patterson at Caltech measured the lead in a piece of the Canyon Diablo iron meteorite and from it determined the age of the Earth: about 4.55 billion years.
Words to know
- meteorite: fallen space rock
- migrated: moved over time
- shockwave: blast of pressure
- asteroids: rocky space rocks
- disk: flat spinning ring
