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A SOLAR SYSTEM IS BORN Chapter 16 – 1 Part 1 The Solar Nebula • Just like clouds in the sky, there are clouds in space. • These clouds are called nebulas. • They are made mostly hydrogen and helium and dust. Gravity Pulls Matter Together • The matter of a nebula is held together by gravity. • There is a lot of empty space between the particles in the nebulas. • So the gravity is very weak. Pressure Pushes Matter Apart • Gravity causes the particles in a nebula to be attracted to each other. • As particles move closer together, collisions cause pressure to increase and particles are pushed apart. • If the inward force of gravity is balanced by outward pressure, the nebula becomes stable. Upsetting the Balance • The balance can be upset if two nebulas collide or if a nearby star explodes. • As the matter collapses inward, the temperature increases and stars begin to form. • This is a solar nebula. • Our sun formed like this. How the Solar System Formed • The solar nebula collapses and begins to spin. • The rotating cloud gets hotter and denser in the middle. • The outer edges of the disk begins to cool. • Dust particles collide and form larger particles. From Planetesimals to Planets • The collision of particles formed bodies called planetesimals. • Their size continues to increase because gravity keeps pulling in material. • All suns, planets and moons are a sphere. • A sphere is that shape because all points on the surface are an equal distance from center. THE END