Planetary System Formation
Our Sun belongs to the generation of stars created 4.6 billion years ago, when
our galaxy was roughly half its present age. A cloud of interstellar gas,
dust, and ices containing several generations of material collapsed to
form the nebula from which the Sun and the rest of our solar system grew.
This collapse may have been triggered by a nearby supernova. Cosmologists
believe that because the material in the nebula was rotating to some degree,
not all of the nebular material fell directly into the central mass that
would become the Sun. Instead, some of the material was confined to a
flat, spinning disk, called a protoplanetary disk, around the young Sun.
As time went on, the grains and ices in the disk bumped into and stuck
to one another. As they grew larger, their gravitational forces increased,
attracting more matter from the disk and gradually building up kilometer-sized
bodies called planetesimals, some of which in turn formed the nuclei of
the planets as we know them today. Other planetesimals became either comets
or asteroids. This protoplanetary disk was thus the transition state between
our stellar ancestors and the planetary objects that evolved from it.
Understanding star and planet formation, detecting other planetary systems, and searching for signs of life on such planets are key objectives of NASA's Origins Program.
The Origins Education Forum is the central node for the education and outreach activities of the Origins Theme of NASA's Office of Space Science. The Origins Education Forum is managed for NASA by the Space Telescope Science Institute.
Reproduced from http://origins.stsci.edu