Solar System The solar system is the gravitationally bound system comprising the sun and the objects that orbit it.

Formation of the Solar System The solar system formed 4.6 billion years ago Gravitational collapse of a giant interstellar molecular cloud. Vast majority of the system’s mass (99.86%) is in the sun, with most of the remaining mass contained in Jupiter.

Four inner planets “terrestrial” planets Mercury, Venus, Earth and Mars Composed of rock and metal

Four outer planets Giant planets Much more massive than the terrestrial Jupiter and Saturn are gas giants, mostly hydrogen and helium Uranus and Neptune are ice giants, mostly water, ammonia and methane

Orbits Elliptical, but nearly circular Flat Within a flat disc called “ecliptic”

Smaller Objects Asteroid belt between Mars and Jupiter Kuiper belt beyond Neptune (ices) Dwart planets (Pluto, Chiron, Ceres, Eris) Solar wind. A stream of charged particles flowing outward from the sun. Oort cloud. Source for comets. Reservoir of ices.

Sun 99.86% of mass of solar system (332,900 times the mass of the earth) Mostly hydrogen and helium Fusion of hydrogen into helium. Main sequence star on Russell Hertzsprung Surface temperature 5500 – 5700 K Radiates yellow and yellow-green light

Inner Solar System Four terrestrial or inner planets have dense, rocky compositions, few or no moons and no ring systems. Venus, earth and Mars have atmospheres that generate weather Impact craters, mountains, valleys and volcanoes

Asteroid belt Between Mars and Jupiter Rock and metallic minerals with some ice Remnants from solar system formation that failed to coalesce because of the gravity of Jupiter Tens of thousands, perhaps millions, of objects over one kilometer in diameter.

Outer solar system Four outer planets or giant planets All four giant planets have rings Jupiter and Saturn are hydrogen and helium gaseous Uranus and Neptune are ices of water, ammonia and methane

Kuiper belt Mostly ice Dwarf planets 100,000 objects with diameter greater than 50 kilometer Pluto, Chiron (moon of Pluto)

Oort Cloud Trillion icy objects Source for comets Move very slowly

Solar System in Milky Way Milky Way is a spiral galaxy with a diameter of 100,000 light years containing about 100 billion stars (10^(11)) The sun is on one of the outer spiral arms between 25,000 and 28,000 light years from the center of the Milky Way. Speed is 220 km/s, so it completes one revolution every 225-250 million years.