Solar system creation

According to astronomers' theories an external factor is sometimes required for a nebula (a gaseous cloud, usually consisting mainly of hydrogen) to collapse and give birth to a star. The factor could be a star passing nearby, posing its gravitational disturbance on the cloud, or even a supernova going off in the vicinity. Astronomers aren't completely in agreement of what could have caused the collapse of the solar nebula. More on stellar formation.

Furthermore, many astronomers also believe that once the centre of the solar nebula started to heat up, it simultaneously started to blow away matter close to it. Since hydrogen and helium are light elements, they were blown far away into the solar disc, thus leaving the heavier elements (silicates) relatively closer to the star. This explains why the four innermost planets (called the terrestrial planets, the earthlike planets) are rocky, while the outer planets are gas giants.

Space art 1 is a view towards the protosun, showing venus to the left, and earth at the distant right. Dust, and rocks are numerous. Gradually they will collide and form into larger and larger objects, protoplanets.

The age of the sun is approximately 5 billion years and the age of the planets is likely similar.
The sun was born at another place in the milky way rather than where it is now. Since its current orbit takes it about 250 million years to complete one cycle, it is extremely difficult for us to know where it was born, and what stars were in that neighbourhood.

The sun is said to be a third generation star, meaning that it contains matter that has been present in two previous stars, because the concentration of heavier elements produced in supernovae is relatively high.


For more information on this topic, see Hadean Earth.

Next: The Sun

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Space Art 1: This is a view of the accretion disc that the sun and the planets were created from. At the left is Venus, and in the distant right is the Earth. The image is a wallpaper (1280*960), 160 Kb.