ORIGIN OF THE SOLAR SYSTEM Chapter 12

MAJOR PROPERTIES OF THE SOLAR SYSTEM l Each planet is isolated about twice as far from the Sun as its inward neighbour. l The orbit of each planet around the Sun is approximately circular. l The planetary orbits lie nearly in the same plane. l The direction of revolution of the planets around the Sun is the same as the Sun’s rotation. l Most planets spin in the same direction except (V, U? and P). l Most moons revolve in the same direction as the planets rotate. l All of the above facts suggest a single formation event.

MAJOR PROPERTIES OF THE SOLAR SYSTEM l All of the above facts suggest a single formation event for the solar system.

MAJOR PROPERTIES OF THE SOLAR SYSTEM l Chemical ä The terrestrial planets are depleted in light elements such as H and He. ä Lighter elements were not able to condense (form solids) near the Sun. These elements escaped from the inner regions of the Solar System.

MAJOR PROPERTIES OF THE SOLAR SYSTEM l Ages ä Meteorites are 4.5 billion years old.

MAJOR PROPERTIES OF THE SOLAR SYSTEM l Ages ä Parts of the Moon are also 4.5 billion years old.

MAJOR PROPERTIES OF THE SOLAR SYSTEM l Ages ä Earth is at least 3.8 billion years old.

FORMATION of the SOLAR SYSTEM Orion Nebula  The Solar System formed about 4.5 billion years ago from the solar nebula.  New stars are currently forming in the Orion Nebula.

FORMATION of the SOLAR SYSTEM   The Eagle Nebula is also a region of current star formation. Eagle Nebula

FORMATION of the SOLAR SYSTEM ä Gravity pulls gas and dust to the centre of the nebula. ä Material spins faster as nebula shrinks. The formation of a star ä Easier for material to fall into the poles than equator. A disk is formed with most of the material collecting in the central region.

FORMATION of the SOLAR SYSTEM ä Disks are observed around many young stars. Protoplanetary Disks in the Orion Nebula ä When the supply of dust and gas is depleted, the collapse of the nebula ceases and the nebula then begins to cool.

FORMATION of the SOLAR SYSTEM ä As the nebula cools, the gas forms heavier compounds. ä Water is formed far from the centre. Its presence on Earth is unexpected.

FORMATION of the SOLAR SYSTEM ä Grains aggregate together to form planetesimals ( km, some still seen as asteroids and comets) Asteroid IdaComet Hale-Bopp

FORMATION of the SOLAR SYSTEM ä In the inner Solar System, planetesimals accreted to form the terrestrial planets. ä Era of heavy bombardment by planetesimals melted planets and caused differentiation.

FORMATION of the SOLAR SYSTEM Primordial Earth glowed from impact generated heat.

FORMATION of the SOLAR SYSTEM ä In the outer Solar System, lots of gas was available. Protopanetary cores accreted huge amounts of gas. Protoplanetary Cores

FORMATION of the SOLAR SYSTEM ä The collapse of the solar nebula and the formation of the planets occurred in a few million years.

FORMATION of the SOLAR SYSTEM ä The collapse of the solar nebula and the formation of the planets occurred in a few million years. ä Lots of planetesimals left in the inner solar system to cause havoc. Mercury Moon

FORMATION of the SOLAR SYSTEM

ä One or more large planetesimals collided with Venus and reversed its spin direction. Venus

FORMATION of the SOLAR SYSTEM ä One or more planetesimals collided with Earth and pulled out enough material to form the Moon.

FORMATION of the SOLAR SYSTEM ä Initially, the Earth had no water. Icy comets hitting Earth brought water and organic compounds from the outer region. Comet West

SHOEMAKER-LEVI COMET

FORMATION of the SOLAR SYSTEM ä Comets continue to impact the planets. Comet Shoemaker-Levi Impact Sites on Jupiter