Hi.
We think the Sun and planets were born out of a huge cloud of gas and dust. The cloud was disturbed somehow (maybe by a near by supernova explosion) and started to collapse. Once the collapse started gravity pulled the material in further. Most of it ended up in the center as the Sun, but some of it remained to form the planets, dwarf planets, comets, and such that make up the rest of our solar system.

There were some chaotic times back in the early solar system with all sorts of preformed bits of planets whizzing about and colliding, but things settled down eventually (although there are still occasional collisions, like that of comet Shoemaker-Levy 9 with Jupiter back in 1994)

You can read about this at the Window to the Universe site:
Solar System Formation
http://www.windows.ucar.e...ystem/formation.html

Terry

hello,

in my astronomy class we have debated which planet was formed first after the star. Some say it was jupiter since it wa the most massive, some say it was mercury because it was closest to the dense cloud that created the sun. What is the current expert opinion on which came first?

thanks,

Steve Eisenlord

Hudson, MA