Why do planets exist?
WHY? Is NOT a question that science answers very well. HOW? IS a
question science deals with very well. Planets form when the dust rocks and
gases surrounding a star begin to clump together. If there isn't enough dust
rocks and gases to form another star by the heat generated by gravity
pulling the "stuff" together, one of the things that can happen if the
formation of planets. Other things can happen, such as the formation of
comets, belts around the star, to mention only two. This deals with the
"how" question, but not with the "why" question?
The answer to the "why" question depends upon ones philosophical and/or
religious perspective. But those questions, science has little to offer.
We are only truly beginning to understand solar system evolution, but this
is what we our data suggests so far: (1) Interstellar dust (possibly from a
star that went nova) naturally accrete - they bump into each other and due
to a lack of any other forces their electrostatic forces make them come
together and form clumps. (2) These clumps start to exert a gravitational
force causing (a) more dust to collect, and (b) impart a rotational force to
the whole interstellar gas system. (3) a massive center forms and this
becomes a star when enough matter collect on it, (4) The birth of a star
blows out excess matter which will in turn swirl around the gravitational
center of the new star. (5) These excess matter will collect on their own
and form planets. Some of them will become gas giants (like Jupiter, Saturn)
and others will be rocky (Mars, Earth). (6) In turn, these planetary centers
may capture other planetoids and make them moons.
Greg (Roberto Gregorius)
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Update: June 2012