Planetesimal Hypothesis Overview

Planetesimal Hypothesis

• Proposed by Thomas Chamberlin and Forest Moulton in 1895
• This hypothesis suggests that the Solar System's planets formed from a collision between the Sun and another star.
• The passing star's gravity caused material to be ejected from the Sun's surface.
• Material ejected from the Sun's near side was thrown farther out into space, similar to the distance of the outer planets.
• Material ejected from the Sun's far side was ejected less forcefully, similar to the distance of the inner planets, or terrestrial planets.
• This ejected material cooled and condensed into solid particles called planetesimals.
• The planetesimals then gradually grew into planets by accumulating and colliding.
• The cores of the planets originated from the inner material ejected from the collision.
• The outer areas of the planets formed from a massive swarm of particles spread outward in a disc-like structure.
• The majority of planet formation occurred in areas where material was more plentiful.
• Smaller, ejected materials were composed of hot gas, which condensed into liquids then cooled into solid particles.

Objections to the Planetesimal Hypothesis

• This theory couldn't explain the massive passing star's proximity to the Sun.
• The alignment of stars in space made the movement between them improbable.
• The theory couldn't account for only nine planets forming, nor explain the differences in planet sizes.