© T Pyle (SSC) / JPL-Caltech / NASA)
This artist's concept depicts a distant hypothetical solar system, similar to the one recently discovered with the Spitzer Space Telescope. A narrow asteroid belt, filled with rocks and dusty debris, orbits a star similar to our own Sun when it was approximately 30 million years old (about the time Earth formed). Within the belt, a hypothetical planet also circles the star.
This artist's concept depicts a distant hypothetical solar system, similar to the one recently discovered with the Spitzer Space Telescope. A narrow asteroid belt, filled with rocks and dusty debris, orbits a star similar to our own Sun when it was approximately 30 million years old (about the time Earth formed). Within the belt, a hypothetical planet also circles the star.
Looking at the planets of the solar system, you could be forgiven for thinking that if they do belong to the same family, it is by adoption rather than kinship. Not so: the story of the solar system's birth reveals that they are blood siblings, all created from the same molecular cloud whose collapse formed the sun. You might also think that these disparate bodies are scattered across the solar system without rhyme or reason. But move any piece of the solar system today, or try to add anything more, and the whole construction would be thrown fatally out of kilter. So how exactly did this delicate architecture come to be?
When our sun formed, it swallowed about 99.8 per cent of the debris cloud around it. According to the generally favoured picture, the lean pickings that remained were sculpted by gravity into a thin disc of gas and dust encircling the newborn star's midriff. As the dust grains of this disc orbited the sun, they collided and progressively coagulated into ever larger bodies. In the disc's innermost region, the ignition and burning of hydrogen in the sun made things very hot, so that only metals and silicate minerals with high melting points were present in solid form. Bodies in that region could only reach a certain size - producing the four small rocky planets of the inner solar system: Mercury, Venus, Earth and Mars.
