SOLAR SYSTEM

Detailed explanation-1: -The Accretion theory The Sun passes through a dense interstellar cloud and emerges surrounded by a dusty, gaseous envelope. The problem is that of getting the cloud to form the planets. The terrestrial planets can form in a reasonable time, but the gaseous planets take far too long to form.

Detailed explanation-2: -Accretion is the process of growth or increase of astronomical bodies due to gravity. Typically it occurs by the gradual accumulation of additional layers of matter. See Formation and evolution of the Solar System for a discussion.

Detailed explanation-3: -The prevailing model for planetary accretion, also called fractal assembly, and dating back as far as the 18th century, assumes that the Solar System’s planets grew as small grains colliding chaotically, coalescing into bigger ones, colliding yet more until they formed planetesimals.

Detailed explanation-4: -Definition of planetesimal While the name is always applied to small bodies during the process of planet formation, some scientists also use the term planetesimal as a general term to refer to many small Solar System bodies – such as asteroids and comets – which are left over from the formation process.