Module 5 Notes
Module 5 Notes Geoscience 115
Popular in Science Behind the News- The World Around Us
Popular in Geology
This 6 page Class Notes was uploaded by Hannah James on Sunday September 6, 2015. The Class Notes belongs to Geoscience 115 at University of Wisconsin - Madison taught by Philip Brown in Spring 2014. Since its upload, it has received 41 views. For similar materials see Science Behind the News- The World Around Us in Geology at University of Wisconsin - Madison.
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Date Created: 09/06/15
Geoscience Module 5 Asteroids and Us Coming Soon The Ultimate extinction machines 0 Valentine s Day 2001 The NEAR Shoemaker spacecraft Near Earth Asteroid Rendezvous landed on the asteroid Eros 0 Observed the asteroid s structure composition gravity and magnetic field for over a year before landing 0 February 22nd 2001 New evidence was found indicating a meteorite or comet in the extinction that marks the PermianTriassic boundary 0 Most asteroids orbit in a circular orbit between Mars and Jupiter 0 They often crash into each other and grind each other to bits Puny but Potent 0 The gravitational effects of planets can occasionally cause an asteroid s orbit to become more eggshaped 0 As the orbit becomes elliptical it could lead to a crosscollision with Earth s orbit or Earth itself 0 Small bits of asteroid that experience these effects could become meteors that brighten our night sky Disaster Flick 0 Most asteroids and comets don t come into contact with Earth 0 But they can effect Earthly events because of the kinetic energy from their enormous speeds 0 Kinetic Energy 12 mass velocity 2 I So a large impact could contain more energy than all the nuclear weapons ever produced The Last BIG One 0 65 million years ago Mass extinction marked the end of the Cretaceous Period and the beginning of the Tertiary Period commonly called the KT boundary 0 The direct cause of the extinction is not known but many predict climate change Too Hot in the hot Tub 0 The global warming of the mass extinction was most likely cause by a major volcanic event 0 The release of greenhouse gases C02 etc 0 Scientists looked at rocks from this time period and found rare materials such as iridium 0 It s possible that extraterrestrial materials were deposited by asteroids that crashed to Earth You Going to Prove That 0 One layer of cosmic dust doesn t prove an asteroid caused the extinction but there is other evidence too O The KT boundary contains shocked quartz crystals with microscopic laminations formed by fast highpressure metamorphism of the mineral change in structurecomposition of a rock by heat or pressure I This quartz is only found at two places on Earth ground zero of atomic bomb explosions and meteor impact craters 0 Boundary also contains soot that comes from a large mass of burning trees and plants 0 If there was an asteroid shouldn t there be an impact scar 0 There is in the Caribbean Sea 1 km beneath younger sediments is the Chicxulub crater I Largest of its kind on Earth 180 km in diameter Ready for another Barney joke 0 Evidence now favors a large meteor striking Earth 65 million years ago 0 Impact of a 1015 km meteor would ve cause a hot shockwave to spread all across North America I Heat wave would ve scorched everything in its path and vast clouds of dust afterwards would ve cooled the planet to extreme temperatures Ouch I Some scientists are still not convinced 0 Although a meteor could ve wreaked havoc at this time can it be directly linked to the widespread global extinction 0 There is evidence that a single catastrophic event was not enough to cause the extinction I Many paleontologists believe that a gradual extinction was already taking place 300000 years before the meteor 0 It s possible that volcanoes were emitting greenhouse gases that were increasing temp of Earth and killing off organisms and then the meteor hit and delivered the final blow to speed up the mass extinction of the dinosaurs O This extinction did however allow other more adaptable mammals to thrive with the dinosaurs gone Company Coming 0 The moon gives more evidence for a meteor crash 0 It s obvious the moon has been struck by many types of interplanetary objects I And the leading theory of the moon s formation was that it was ejected from Earth after it was struck from an angle by a piece of debris the size of Mars in the first 50100 million years of its life I Asteroids in the asteroid belt often crash into each other while orbiting so finding one larger than 1 km is rare 0 While asteroids that depart the belt can be dangerous to Earth they are eventually pulled by the sun s gravity into fiery oblivion A Striking Possibility I The odds of an asteroid s collision with Earth are rare 0 Space it too big for these objects to be a common threat 0 However since most asteroids are unknown the assurance against a collision is not ironclad 0 Approx 1500 to 200 asteroids larger than 1 km in diameter are orbiting near Earth most are not identified I This fact has spawned an asteroidsearch industry to find NEOs Near Earth Objects 0 NASA has a budget of 3 million for its asteroid search Searchin Searchin Gotta find a place to hide I Asteroids are hard to see 0 They re ect little light and are always on the move so you have to scan the same patch of sky to look for changing objects against the static background of stars I Some researchers look for light in the visible or infrared bands I Others use radar to bounce radio waves off the asteroids and rea the return signal uses the Doppler Effect to determine its distance from Earth 0 Efforts I LINEAR Lincoln Near Earth Asteroid Rsesearch is a satellite tracking telescope that can see the entire sky in 12 nights I When it began in March 1998 LINEAR saw 13 new near Earth objects 0 However asteroids and comets are constantly coming into view and the telescope still cannot see faint be possible destructive asteroids I The Catalina Project by U of Arizona has worked for the past 12 years to identify unknown asteroids Don t Wanna Live there but a great place to visit 0 Scientists have no visited asteroids 0 The spacecraft Galileo took pictures of asteroids Ida and 951 Gaspra O 27 June 1997 NEAR took pictures of 253 Mathilde a main belt asteroid O 7 planned missions to visit and even return samples from 26 asteroids over the next 13 years A little knowledge Dangerous 0 What could we do if an asteroid did threaten the Earth 0 Smashing a housesized piece of basalt into a 17 km asteroid would do nothing and no one knows how to accelerate an object to asteroidblasting speed 0 We need alternatives A lively alternative I Asteroids are worth studying because they are our best chance at viewing the composition of the primordial solar system 0 85 of meteors that have crash landed to Earth are identical to the makeup of Earth s mantle 15 have the iron and nickel of Earth s core I This is similar to the 8020 volume ratio of mantle to core on Earth I When Earth was first forming asteroids and comets were bombarding the Earth so often that life could never have survived 0 Only after 38 billion years when the bombardment tapered off did the water and organic molecules that make up the building blocks of life appear Friend of Foe 0 The bombardment may have suppressed life for a time but it may also have provided the water and carbon molecules needed for life to begin I Comets and asteroids are still crashing to Earth and they contain around 10 of organic molecules 0 While most burn up and disintegrate or at least become hot enough to kill all the organic molecules the right size meteor could ve made it to Earth with its organic molecules intact Shock Therapy 0 These extraterrestrial objects could ve also provided the energy needed for complex organic molecules to form 0 Earth s atmosphere used to contain large amounts of CH4 N2 and H20 I The organic molecules necessary for life are larger versions of these whose development requires energy in the form of heat I These impacts could ve formed the first organic molecules Spacy Spin Doctor 0 Scientists view asteroids as remnants of the protoplanetary disk which was the disk of gas and dust that formed the sun and planets 46 billion years ago 0 When large objects coalesced some dregs remained These dregs became asteroids and now orbit between Mars and Jupiter 0 The asteroid belt divides the solid planets Mercury Venus Earth Mars and the gas planets Jupiter Saturn etc I The nature of asteroids remains unclear are they solid or agglomerations of rock gas and dust 0 Results from a J PL Jet Propulsion Laboratory team show that one asteroid 1998 KY26 is solid rock 0 Radar data on the asteroid showed it must be monolithic formed of a single type of rock and must have tensile strength ability to resist stretching I The reasoning is that asteroids have very weak gravity and a debris pile would selfdestruct by centrifugal force if it were to rotate faster than every two hours this asteroid rotates in less than 11 minutes All Together Now 0 Proof that asteroids are solid links them to meteorites which are also solid rock and which presumably originated in asteroids 0 Until now there has been no proof that asteroids had the same solid construction as meteorites 0 How did the protoplanetary disk fuse into solid rock 0 Planets have enough radioactive decay and mass to make and retain this fusion I But in the freezing asteroid belt heat for fusion may have come from the rapid decay of radioactive isotopes like aluminum26 during the first billion years of the solar system I It could ve also come from solar wind and planetary magnetism 0 Studies of meteorites found that they came from rocks that cooled at the rate expected for objects at least 100 km in diameter 0 This means that original asteroids were much bigger and their smaller size now is a result of continual collisions in orbit I Several moons in the solar system may be leftover asteroids 0 There is evidence that some asteroids had liquid water near their surfaces early in history 0 Today temperatures of the asteroid belt are 260 degrees Celsius I Because of the heating mechanisms stated above the belt would ve been much hotter earlier in history and was apparently hot enough to melt ice without immediately evaporating water Orbital Oddities 0 Distinctions used to be neat asteroids were rocks comets were dirty snowballs 0 But new data is making the distinctions murky a class of 3 objects that were originally called comets may be asteroids 0 Like all comets these three things have tails I But they each lack a coma I By analyzing the tails it became apparent that the bodies had been blasted by an impact which shook loose some dust which slowly expanded to become the tail 0 So the comets were actually asteroids 0 This data shows that asteroids suffer cataclysmic collisions that form families of smaller asteroids and that collisions that gouge their surfaces stir up dust and debris without necessarily busting them apart I This hints towards major diversity for comets and asteroids Like Chaotic 0 Why are most asteroids stuck in orbit while only a few escape and cross Earth s orbit 0 Some asteroids become pulled by Jupiter s gravity making their orbit more elliptical eggshaped I Eventually they would start crossing Earth s orbit A Temporary Asteroid 0 Asteroids are only temporary once they cross Earth s orbit because the sun s graVity pulls them in 0 But if asteroids are supposed to be temporary then Jupiter s graVity cannot solely explain the number of asteroids that cross Earth s orbit Brother can you spare a planet 0 Original computer simulations of asteroid orbits ignored the pull of the inner planets 0 But adding their pull to the simulations made more asteroids cross Earth s orbit and made the number more similar to actual calculations 0 Mars with only 14 of Jupiter s graVity plays a major role in asteroid orbits O Explanation could be chaos means that small perturbations disturbances can cause large changes in orbits
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