Don Babbie of Covina, Califnrniaj for is question:

What is the Planetesimal Hypothesis?

Let's not be scared by those two long words    hypothesis and planetesimal Let’s just pry out their secrets with a little word detecting, find, since we need a starter or working idea to solve any problem, let’s begin from the planet section of these words.

If our working idea is right, then planetesimal must be something to do with planets. And so it is. It can mean either a planet body of infinitesimal size, or something about such a minute body. The word hypothesis we understand already because we just used one. We used the word planet as a working hypothesis to reason out the meaning of the word planetesimal. The planetesimal hypothesis, then must be an idea up for argument concerning planets. Actually, it is one of the several theories set forth to explain the origin of our solar system,

This hypothesis suggests that our planets were formed when a great star once came within pulling distance of our sun. Even far apart two such massive stars would exert terrific gravitational pull upon each other   enough to pull out long streamers of gases into space„

Clouds of such gases it is argued, left the sun in two great arms, One was drawn from the side facing the visiting star. The other, like the backwash from a huge tide, was thrown off from the opposite side. The visitor is said to have come close in a curves swung around the sun and march off into the far distance, If so, streams of gaseous material must have been pulled and thrown out continuously and in several directions.

As it swung around, the passing star is thought to have given a right angle twist to the flowing streamers and sent them spinning around the sun in the same directions never to be drawn back by its powerful gravitation.

Out in spaces the seething gases are said to have cooled into solid particles. The solid particles collided and were held together by their own gravitation as planetesimals circling the sun.

Planetesimals collided and held together to form planets and planets captured smaller bodies as satellites. The bumps and the collisions of this building process tended to round off the orbits of the planets into almost circles,

The theory explains the millions of meteors that strike our air as part of the original planetesimals. It says that though the great drama of the visiting star may have happened millions of years ago the final sweeping up of the pieces is still going on.

Though this great theory suggests many possibilties about the origin of our planets. But it does not explain everything and it certainly is not proven. So far, no one has proved how the planets originated ands until this is done, every working idea must remain a hypothesis,