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Earthsci Review - Ch 12,13

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Earth Sciences
Earth Sciences 1086F/G
Natalie J.Allen

EARTHSCI FINAL EXAM REVIEW UNIT 4 Intro Discovery of Ceres  People started looking for large and small “floating” debris, and in doing so discovered that there was a remarkable space between the planets Mars and Jupiter. According to the mathematical relationship of planet positions in the solar system (see Titius-Bode Law), there really should be another planet in that space  1801: discovery of the first object in that space was made by Giuseppe Piazzi, a monk but also the director of the Palermo Observatory in Sicily. He named that asteroid Ceres which has now been classified as a dwarf planet. Definitions · Asteroid: a natural rocky object in space measuring 100 m to several hundred kilometres in diameter. · Meteoroid: a natural rocky object in space measuring from a few millimetres to 100 m in diameter. · Meteor: the visual streak of light associated with passage of a small meteoroid through Earth`s atmosphere; the heat energy producing the light is a result of friction between the object and molecules of gas in the atmosphere. Remember – a meteor is not the object, only the light phenomenon. · Fireball: the light associated with a large meteoroid or asteroid as it interacts with the atmosphere. · Meteorite: a fragment (any size) of either a meteoroid or asteroid that lands on Earth`s surface. Please remember – it is not called a meteorite until it actually lands on surface. Titius-Bode Law (Rule)  Mathematical sequence to explain relationships between planet orbits  How it works: 1. Take the simple mathematical series 0, 3, 6, 12, 24, etc. Note that each successive number is double the previous one. 2. Add 4 to each of the above, getting: 4, 7, 10, 16, 28, etc. 3. Now divide each of the above numbers by 10 to get: 0.4, 0.7, 1.0, 1.6, 2.8, etc. These are the predicted planet spacings in Astronomical Units. Chapter 12 Main Asteroid Belt – asteroids are found between the gap of Mars and Jupiter  Jupiter’s mass had an enormous effect on the motions of small bodies anywhere close to it because of its gravity.  Gravitational perturbations (i.e., disruptions) caused by Jupiter`s gravity prevented any of those objects from merging into a single planet-sized body.  Gradually, over a long period, each asteroid is influenced by these forces to change its position and swing either out ward or inward from Jupiter, leaving behind a gap (Kirkwood gap - gaps in the belt where no asteroids seemed to exist) where it used to be. Asteroids or meteoroids entering the Kirkwood gaps are booted out by Jupiter’s gravitational disruption forces so great they completely escape the limits of the Asteroid Belt. Classification  First, we can base a classification scheme upon meteorite samples of the asteroids.  Second, we can base our classification upon the characteristics of sunlight (albedo) reflected off the surfaces of asteroids. (albedo = proportion of light reflected from an object; the range is 0 (perfectly black) to 1 (perfectly reflecting))  Third, astronomers and other scientists have constructed pretty sophisticated instruments which break down the reflected light into a whole spectrum, thus collecting rough element analyses of surfaces as well as simple albedo numbers 3 Main Groups of Asteroids:  C-type asteroids – high carbon content or ‘carbonaceous’, 75% of known asteroids; roughly similar composition to Sun, minus the volatile elements. (located on outer asteroid belt)  S-type asteroids – high silicon or ‘silicaceous’, 17% of known asteroids.  M-type asteroids - metallic, most of the remaining asteroids. It’s important to learn whatever we can about asteroids because:  They represent very primitive material left over from formation of the solar system  Much water and organic material came to Earth from them  Sooner or later a large asteroid impact is likely to put an end to many terrestrial  species (including humans) carbonaceous asteroids: with dark carbon minerals on their surfaces. Have the most meaning for us of all the different types of meteorites. How do we get the Composition? 93% of meteorites are composed of minerals called silicates (i.e., silicon plus oxygen plus some other elements) and most of the rest are pure metal (mostly iron with a bit of nickel).  Meteorites will have similar spectral reflectance characteristics of the asteroid they came from  To test this, investigators selected several basic kinds of meteorites and obtained laboratory reflection of spectra of the powders and compare them with those from the asteroid.  When the reflection spectra compared with laboratory spectra of meteorite samples, it must be remembered that the spectrum is not from a single mineral but from several at one time  This tends to "muddy" the resulting spectrum, since it is really composed of several overlapping spectra  But for the moment, identifying the exact mineral composition at the surface of the asteroid is not as important as finding a close spectral match between asteroids Where meteorites come from  Samples of asteroids and cores of “dead” comets  Samples blasted from the surfaces of Moon and Mars Does the distribution of asteroid types match distribution of meteorite types collected on Earth?  The disparity between the carbonaceous chondrites, rare on Earth but plentiful in the asteroid belt, and the ordinary chondrites, common on Earth but relatively rare in the asteroid belt, indicates that chondrites probably came from one or at most a few parent bodies  The large numbers reaching Earth are apparently not indicative of large numbers of S-type asteroids in space. It see
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