3A Objectives Describe the nebular theory in detail. List steps involved and describe physical processes needed Describe jovian and terrestrial planets List planets in each category

Nebular Theory A hypothesis concerning the origin of the solar system according to which a rotating nebula cooled and contracted, throwing off rings of matter that contracted into the planets and their moons, while the great mass of the condensing nebula became the sun.

Before our solar system… Extremely large star supernova Variety of heavy elements are dispersed into space Nebula forms with these heavy elements According to Nebular Theory, the sun and planets form from this nebula creating our solar system as we know it today

Contraction of Nebula Solar system formed about 4.6 billion year ago, when gravity pulled together a low-density cloud of interstellar gas and dust As the collapse proceeded, the rotation speed of the cloud was gradually increasing due to conservation of angular momentum. Ice Skater Spinning

Nebula Collapse into Rotating Disk Gravitational collapse was much more efficient along the spin axis, so the rotating ball collapsed into thin disk Most of the mass concentrated near the center

Protosun As the cloud contracted, its gravitational potential energy was converted into kinetic energy of the individual gas particles Collisions between particles converted this energy into heat

Protosun The solar nebula became hottest near the center where much of the mass was collected to form the protosun The collisions among the atoms were so violent that nuclear reactions began, at which point the Sun was born as a star

Why does the sun not pull apart? The Sun reached a a balance between the gravitational force and the internal pressure, aka as hydrostatic equilibrium

Planets The first solid particles were microscopic in size Gently collisions allowed the flakes to stick together and make larger particles which, in turn, attracted more solid particles This process is called accretion

Planets After a few million years, these clumps were the size of small cities The clumps continued to grow in size until they became considered protoplanets

Planets Near the Sun, where the temperature was higher, only the heaviest compounds condensed forming heavy solid grains, including compounds of aluminum, titanium, iron, nickel, and, at somewhat cooler temperatures, the silicates In the outskirts of the disk the temperature was low enough that hydrogen-rich molecules condensed into lighter ices, including water ice, frozen methane, and frozen ammonia

Terrestrial Planets In the warmer inner solar system, protoplanets formed from rock and metal, materials cooked billions of years ago in cores of massive stars These protoplanets lost most of their light elements due to the immense heat from the sun (little H & He) Mercury, Venus, Earth, and Mars These elements made up only 0.6% of the material in the solar nebula (and the faster collisions among particles close to the Sun were more destructive on average), so the planets could not grow very large and could not exert large pull on hydrogen and helium gas. Even if terrestrial planets had hydrogen and helium, proximity to Sun would heat gases and cause them to escape. Hence, terrestrial planets (Mercury, Venus, Earth, and Mars) are dense small worlds composed mostly from 2% of heavier elements contained in solar nebula

Mercury, Venus, Earth, Mars

Jovian Planets In the outer solar nebula, protoplanets formed from ice flakes in addition to rocky and metal flakes Because of the lack of heat from the sun Since ices were more abundant the protoplanets could grow to much larger sizes Jupiter, Saturn, Uranus, and Neptune

Jovian Planets Because they had so much more mass, they were able to capture large amounts of H & He They became the large, gaseous, low-density worlds rich in hydrogen and helium, with dense solid cores Jupiter

Moons The same process that formed the solar nebula -- contraction, spinning, flattening and heating -- formed similar but smaller disks of material around these planets called satellites or moons

Moons Double planet hypothesis: The planet and its moon assembled independently at same time from the same rocks and dust. Capture hypothesis: The moons formed elsewhere and then were captured by planetary gravity

Our Moon Impact Theory Giant impact of large body with young Earth explains Moon's composition