Formation of Our Solar System

Part of Hall of the Universe.

Formation and evolution of the solar system_HERO AMNH/D. Finnin

The Sun and the planets formed together, 4.6 billion years ago, from a cloud of gas and dust called the solar nebula. A shock wave from a nearby supernova explosion probably initiated the collapse of the solar nebula. The Sun formed in the center, and the planets formed in a thin disk orbiting around it. In a similar manner, moons formed orbiting the gas giant planets. Comets condensed in the outer solar system, and many of them were thrown out to great distances by close gravitational encounters with the giant planets. After the Sun ignited, a strong solar wind cleared the system of gas and dust. The asteroids represent the rocky debris that remained.

Size and Time Scales of the Solar System

The Earth revolves around the Sun at a distance of 150 million kilometers (93 million miles).

The orbits of the planets are nearly circular, and measure from one-third to 30 times the size of Earth's orbit.

Mercury, the innermost planet, orbits the Sun in about three months, while Neptune takes 165 years.

The Sun contains about 99.9 percent of all the mass of the solar system.

processes image 1 - collapse and rotation
The slowly rotating solar nebula collapsed under its own gravity to form a rapidly rotating disk, with the Sun at the center. Collisions of gas and dust within the disk concentrated the material into a thin plane.
processes image 2 - condensation
The inner region of the solar nebula was hot, allowing only rocky material to condense. The rocky terrestrial planets formed there. Gases and ice could condense in the cooler outer regions, where the gas giant planets and their icy moons formed.
processes image 3 - accretion
Small bodies collided and stuck together to slowly build up the terrestrial planets. Such accretion also built the cores of the gas giants until they were massive enough for their gravity to capture the abundant gases.
processes image 4 differentiation
The terrestrial planets, as well as the larger moons and asteroids, have spherical layers that were created by melting and differentiation. Heavier elements sank to the center, forming iron-rich cores. Lighter materials were buoyed upward to form the outer rocky layers.