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Download Goal: To understand how Saturn formed and what its core is like
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Goal: To understand how our solar system formed and what it like today Objectives: 1) Formation of stars 2) Solar Nebula 3) Terrestrial Planets 4) Gas Giants 5) Other debris 6) Orbital motions In the beginning • All you have is a large cloud of dust and gas. • This cloud is very large and very cold. • They are called Giant Molecular Clouds. • Somehow the cloud collapses. The initial cloud • Is made of mostly Hydrogen (~90% by weight). • Most of the rest is Helium (9%) • 1-2% are everything else (in Astronomy we call the everything else “metals” including Oxygen). • The cloud has some spin. What will that do? Spin city • The small amount of spin acts like a merry-go-round. • Much like on a merry-go-round, this spinning motion pushes things outward. • However, nothing stops the collapse in the vertical direction, so the cloud collapses to a disk. • The gas in the disk is literally in orbit around the center of the gas cloud. Disc • The cloud which will form the sun quickly collapses to a spinning disc. • The particles that can get into orbit around the forming star in the middle (called a protostar) survive. • The rest get gobbled up when they fall to the center. Waves • Density waves form in the cloud. • These waves will lead to the formation of the planets. Terrestrial Planets • The inner part of the disk is hot. • The only materials that can be solid in this heat are rocky materials such as iron and silicon. Tar Line • At some distance carbon compounds can become solid and form tarry substances. • This distance is called the tar line. • There is a lot more carbon than there is iron and silicon in the cloud forming the sun. • So, even though there is less material overall to form a planet at this distance a much larger percentage of it becomes solid. • This allows you to build much larger planets! Ice Line • Similar to the tar line but is the point where materials such as water, ammonia, and methane can freeze. • Since there is a lot more of this than carbon even it allows you to build large planets. Gas Giants – rocky stage • During this stage you start out with small “dirty snowballs”. • These snowballs are half rock and half ice. • In time they fuse with other snowballs to make larger snowballs. • In a few million years they will form the core of a gas giant which is about the size of the earth but ten times the mass of the earth. Run Away Accretion • Once the core of a gas giant becomes 10 earth masses it can capture and hold onto gas. • Most of the gas is Hydrogen and Helium, so this is pretty tough to do. • There is a LOT of gas. • There is far more gas than everything else. • So, at this point it grows very quickly. And they are off to the races! • Since Jupiter was outside the tar line (carbon line) but inside the water line at this time Saturn might have hit the runaway phase first. • Once it did, it was a race against time to gobble up material before the sun is officially born and blasts all the remaining gas out of the solar system. Formation of Major Moons • While gas giants are in their runaway accretion phase they form an accretion disk of dust and gas and ice (similar to the accretion disk around the sun). • Much like planets form around the sun so too would the major moons form around gas giants. Minor Moons • The minor moons would have been captured either during this earliest era where there was a lot of debris and Neptune and Jupiter tossing stuff around. • Others could have been captured comets later. • All orbit the planet backwards (retrograde). Additional debris - asteroids • There are regions of space that do not form planets. • One is our asteroid belt. • In this region gravity from Jupiter would have made rocks that hit each other break each other apart instead of make bigger rocks. Additional debris - TNOs • In the outer solar system just beyond the orbit of Neptune there are objects known as Trans-Neptunian Objects (TNOs). • These did not have enough time to form into a planet. Additional debris – Oort Cloud • Some objects were tossed into enormously large orbits by the gas giants (cough – Jupiter – cough). • These orbits can go out as far as a light year. • This is the source of long period comets. Orbits of Planets • In our solar system all of the planets orbit in the same direction and in the same plane. • The planets are held into place by gravity. Gravity • As you move further from an object the gravity it exerts on you decreases by the distance to its center squared. • So, planets that orbit further from the sun have less gravity exerted on them (in terms of acceleration) Conclusion • We have explored the formation of our solar system and how that affects the composition and distribution of its planets. • We have also explored the basics of our solar system.