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ASTR - Chapter 8 Reading Notes

by: Kara Ott

ASTR - Chapter 8 Reading Notes ASTR 11200

Marketplace > Rowan University > ASTR 11200 > ASTR Chapter 8 Reading Notes
Kara Ott
GPA 4.0
Exploration of the Solar system
Andrew Watson

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Exploration of the Solar system
Andrew Watson
Class Notes
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This 17 page Class Notes was uploaded by Kara Ott on Monday October 5, 2015. The Class Notes belongs to ASTR 11200 at Rowan University taught by Andrew Watson in Fall 2015. Since its upload, it has received 17 views.


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Date Created: 10/05/15
Chapter 8 Formation of the Solar System 0 Hypotheses that make sense at one point might be later dismissed because they fail to explain new data 0 Four criteria for success of our SS formation theory 0 MUST explain patterns of motion 0 MUST explain why we have 2 categories of planets o MUST explain existence of huge numbers of asteroids comets o MUST explain why there is room for some exceptions 0 German philosopher Immanuel Kant and French mathematician Pierre Simon Laplace both individually proposed the idea that 88 formed from gravitational collapse of interstellar cloud of gas This became known as the nebular hypothesis and in late 20th century became nebular theory 0 The interstellar cloud of gas mentioned in the nebular theory is called the solar nebula which collapsed under its own gravity 0 That gas was the product of billions of years of galactic recycling that occurred before the sun and planets formed o By studying composition of the sun other stars the same age and interstellar gas clouds we learned that the gas that made up the solar nebula contained about 98 H 85 He and 2 all other elements combined 0 Spectroscopy shows that old stars have smaller proportion of heavy elements than younger ones 0 The collapse of the solar nebula may have been triggered by a cataclysmic event such as the impact of a shock wave from the eXplosion of a nearby star 0 Three processes that altered density temperature and shape as the solar nebula shrank 0 Heating temperature increased gravitational energy gt kinetic energy gt thermal energy the Sun formed in the middle where temp 85 density was highest 0 Spinning increase in rotation rate represents conservation of angular momentum the greater the angular momentum the more spread out it will be 0 Flattening natural consequence of collisions between particles in spinning cloud random motions of original cloud became more orderly as cloud collapsed and changed lumpy original shape into a attened disk 0 Planet formation required the presence of seeds or solid bits of matter from which gravity could build planets 0 General process of solid particles forming in a gas is called condensation 0 Different materials condense at different temperatures 0 Four major categories of solar nebula 0 Hydrogen and helium 98 of solar nebula I These never condense in space 0 Hydrogen compounds 14 of solar nebula I Can solidify into ices when temp is under 1 50 K 0 Rock 04 of solar nebula I Condense into solid bits of mineral between 500 K and 1300 K 0 Metal 02 of solar nebula I Condense into solid form between 1 000 K and 1600 K o H and He gas made up most of solar nebula s mass so it mostly remained gaseous at all times 0 Hydrogen compounds could condense into ices only beyond the frost line distance that it was cold enough to condense which is between Mars and Jupiter aka the asteroid belt 0 Total amount of solid material was far greater beyond the frost line than within it which is why j oVian planets are larger than terrestrial ones 0 Accretion process of small seeds becoming planets o Particles at first were too small to attract each other gravitationally so they stuck together through electrostatic forces or static electricity 0 They eventually grew big enough to be considered planetesimals meaning pieces of planets 0 Only largest planetesimals avoided being shattered and were able to grow into terrestrial planets o Observational evidence comes from meteorites which are rocks that have fallen to Earth from space 0 Because of the large masses of the planetesimals they were able to capture some of the H and He gas of the solar nebula which made their gravity stronger o Moons that accreted from ice rich planetesimals ended up with nearly circular orbits in the same direction as their planet s rotation and lying close to planet s equator o The vast majority of H and He gas was cleared away by combination of intense radiation from young Sun and solar wind which is a stream of charged particles continually coming out from Sun 0 Clearing of gasses made it so that H compounds were not able to eventually condense in the inner 88 which would have changed the nature of the terrestrial planets completely 0 Each full rotation of the sun takes about a month We eXpect that it used to rotate very quickly So we know that angular momentum of the sun must have been transferred to another object because angular momentum cannot just disappear 0 We cannot prove that but evidence comes from observing other stars 0 Many asteroids and comets in our 88 are the leftovers from era of planet formation 0 When impacts occur on solid worlds they leave behind impact craters meaning they have transformed the landscape of the planets 0 Heavy bombardment is when every world in our 88 must have been pelted by impacts and where most crater we see on the moon and other worlds must have come 0 Water and other H compounds were brought to Earth by impact of water bearing planetesimals that formed father from the Sun 0 We think most of the exceptions to the rules came from collisions or close gravitational encounters 0 An object cannot switch from unbound orbit to bound orbit without losing orbital energy 0 Capture process cannot explain our Moon because it s too large to have been captured by small planet like Earth 0 Moon s density is considerably lower than Earth s which tells us that it has very different average composition and could not have been formed simultaneously with the Earth 0 Giant impact hypothesis suggests that Mars sized object hit Earth at speed and angle that blasted Earth s outer layers into space 0 Accretion in this ring of the outer layers oating in space could have formed the Moon 0 Support of this hypothesis comes from the Moon s overall composition being similar to Earth s outer layers and the Moon having a much smaller proportion of easily vaporized ingredients than Earth 0 This hypothesis may also explain other exceptions to general trends ie Mercury s metal core extending to 85 of its radius so maybe the outer layers were blasted off by impact 0 Basically chaotic processes that happened during planet formation including many collisions than surely occurred are expected to have led to a few exceptions o The final stages of accretion and giant impacts in particular are inherently random and probably wouldn t happen again in the same way 0 Planets began to form just over 45 billion years ago a fact that we learned by determining age of oldest rocks in 88 0 Age of rock is time since its atoms became locked together in their present arrangement which in most cases means the time since the rock solidified o Radioactive dating method we use to measure rock s age 0 Example to explain radioactive dating Potassium 4O 19 protons 21 neutrons decays and one of its protons turns into a neutron therefore it now has 18 protons and 22 neutrons and is now Argon 40 0 Any radioactive isotope like Potassium 40 will generally change into its daughter isotope at a steady rate So if you watch this process for a few years at most you can use the rate to calculate the halflife which is the time it would take for half of the isotope to decay into the daughter isotope Many times rocks have multiple isotopes so agreement between the ages found when using radioactive dating tells us that we have dated the rock correctly Meteorites have not melted or vaporized since they first condensed in solar nebula the oldest ones show that they formed about 455 billion years ago which marks beginning of accretion in solar nebula age of 88 is 455 billion years


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