Accretion
Planetesimals. Within the solar nebula, dust and ice particles embedded in the gas moved, occasionally colliding and merging. Through this process, called accretion, these microscopic particles formed larger bodies that eventually became planetesimals with sizes up to a few kilometers across. In the inner, hotter part of the solar nebula, planetesimals were composed mostly of silicates and metals. Formation of planetesimals. Introduction. Terrestrial planets are thought to be built up through the collisions of many smaller objects. Our story begins in the remains of the stellar accretion disk which, for a sun-like star, is 99% gaseous hydrogen and helium by mass. In the outer parts of the disk, gas and dust formed small astroid-like and comet-like bodies called PLANETESIMALS. These formed the building blocks of the planets. A planetesimal is an object formed from dust, rock, and other materials. The word has its roots in the concept infinitesimal, which indicates an object too small to see or measure. Planetesimals can be anywhere in size from several meters to hundreds of kilometers. Planetesimals. Planetesimals. Planetesimals are small bodies of rock and/or ice that form by accretion in the protoplanetary disk s of protostellar systems. These small objects continue to accrete and merge until finally a planetary system is formed.
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planetesimals are formed by a process called?