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GEOL 208 Lecture 1

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GEOL 208 Lecture 1

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  1. 0 Geology 208: The Earth, Moon and Planets • Today • Chap. 15: 388-411 • Next class (May the 12th) • Origin, cont’d, chap. 15: 388-411 • Geology of the Earth: Skinner (TBA) “The Origin of the Solar System”

  2. Aim of the Course To describe, discuss & evaluate the various hypotheses associated with the origin & evolution of the solar system & its constituents: terrestrial planets, gas giants, moons & small bodies • You must be prepared to… • be perplexed & ask questions • have questions answered and remain perplexed • raise follow-up questions for which there are no firm or unambiguous answers • perplex me!

  3. Our Solar System: tidbits 0

  4. Survey of the Solar System 0 Relative planet size Assume, we reduce all bodies in the solar system so that the Earth has a diameter of 0.3 mm. Sun = ~ small plum --------------------------- Mercury, Venus, Earth & Mars = ~ grains of salt ---------------------------------------- Jupiter = ~ apple seed Saturn = ~ slightly smaller than “apple seed” ------------------------------------------------------ Pluto? = ~ speck of pepper

  5. Two Kinds of Planets The planets of our solar system can be divided into 2 very different kinds Terrestrial (earth-like) planets: Mercury, Venus, Earth & Mars Jovian (Jupiter-like) planets: Jupiter, Saturn, Uranus & Neptune 6/3/2014 5

  6. Terrestrial Planets • Four inner planets • relatively small in size and mass (Earth is the largest & most massive) • rocky, scarred surfaces • atmospheres non-existent dense/inpenetrable to visible light • surface temperatures freezing boiling • paradox…- surface environments of • Venus, Earth & Mars • could have been • habitable & watered • early in their geological histories 6/3/2014 6

  7. Gas Giants Much lower average density Mostly gas… no solid surface All have rings (not only Saturn!) 6/3/2014 7

  8. http://shayol.bartol.udel.edu/~rhdt/diploma/lecture_8/io-volcano.gifhttp://shayol.bartol.udel.edu/~rhdt/diploma/lecture_8/io-volcano.gif Moons http://w-uh.com/images/Titan.jpg (a) Europa (b) Titan (d) Io (c) Earth’s Moon • Disparate Environments • buried ocean • surface lakes • frozen desert • (d) rampant volcanism 6/3/2014 8

  9. Our Solar System: tidbits (FYI): H20 density = 999kg/m3 at 100 C

  10. Planetary Movements 0 All planets in almost circular orbits (elliptical) around the sun, in approx. the same plane (ecliptic) Orbits/revolution (counter-clockwise) generally inclined by no more than 3.4o: - except Mercury (7o); Pluto (17.2o) Mercury Venus Mars Rotation counter-clockwise (with exception of Venus, Uranus & Pluto) Jupiter Earth Uranus Saturn Pluto Neptune (Distances and times reproduced to scale)

  11. Astronomical Units (AU) 1 AU (distance from sun to the Earth) = 149,598,000 (1.49 x 108 km) Distance from Earth to nearest star (Alpha Centauri) = 4.42 light years 1 light year = 1013 km = 63,000 AU

  12. Space Debris? 0 In addition to planets, small, irregular rocky bodies orbit the sun - Asteroids - Most asteroids(20,000 identified so far) reside between Mars & Jupiter in the “Asteroid Belt” (2.8 AU) - debris that never accreted into a planet? Since 1992, 1000 small, dark icy “Kuiper belt” objects have been found orbiting beyond Neptune & Pluto… - tip of the iceberg! -

  13. New Planetary Classification • Dwarf Planet • celestial body orbiting sun; not a satellite • massive enough to be rounded by its own gravity • has not cleared neighbouring region of planetessimals

  14. Comets 0 Icy nucleus Highly elliptical orbits Oort Cloud origin? - 100,000 AU from the sun -

  15. http://www.miguelperezsenent.com/Media/Tutorialfiles/tut_meteor/meteor.jpghttp://www.miguelperezsenent.com/Media/Tutorialfiles/tut_meteor/meteor.jpg http://thecrazynews.files.wordpress.com/2007/08/meteorite1.jpg 0 Meteorites - leftovers from solar system formation - Small (mm – mm sized) dust grains throughout solar system (when in space, called “meteoroid”) “meteor” = streak of light in the sky “meteorite”= meteoroid that survives plunge through atmosphere - most weigh less than 1 gram

  16. 0 Impact Craters Moon farside (4 GYA) Mars - lobate crater (age?) Meteor Crater, Arizona (49 KYA) • Craters(like on our Moon’s surface)- common on hard-surfaced bodies in the Solar System - • absent on Jovian planets (gas giants)

  17. Geological Dating (Age) by Crater Counts Elysium Planitia, Mars Moon farside secondary craters, difficult to distinguish from primaries …upsets traditional crater-count/landscape-age hypothesis MOC images showing secondary craters from Zunil. (A) shows part of M02-00581 at 5.9 m/pixel; image is 3 km wide. (B) shows part of the same region as in the bottom of (A) at 1.48 m/pixel from image E04-02119; image is ∼1 km wide. (C) shows large Zunil secondaries (up to 150 m diameter) in a portion of M21-00420 at 5.9 m/pixel; image is 3 km wide. (D) shows tight clusters of craters in part of M16-00228 at 1.47 m/pixel; image is ∼1.1 km wide. Probably only the small craters with bright ejecta in (D) are from Zunil, superimposed on a previously-cratered plain.

  18. 0 Age & Radioactive Dating http://www.astro.virginia.edu/class/skrutskie/images/ssform_artist.jpg • …common ages of Sun, planets, moon, meteorites… (4.6 GY) • - measures of age - • radioactive dating of rocks, oldest Earth rock is 4.3 GY (somewhat accurate) • crater counts on Mercury, Mars & the Moon (less than somewhat accurate)

  19. Age by Radioactive Dating • Formation/solidification of rocks incorporates fixed % of known elements • radioactive elements decay according to fixed schedule • evaluate ageby measuring abundance of radioactive element in a rock • c. ½ life of a radioactive element = time taken for ½ of atoms to decay • i.e. uranium-238, decays into lead isotope (lead-238) • ½ life of uranium-238 is 4.5 GY • d. if a rock contains 50% uranium-238 & 50% lead-238, then the rock must be 4.5 GY

  20. The Origin of the Solar System • Observation & theory: the foundations of science • 2. Science & the power of “1” ? • 3. Cosmology 6/3/2014 20

  21. Solar System Formation: by catastrophy • a. Passing-star hypothesis • origin of planetary material • star passing close to the sun, tears material from the latter …but stars are small compared to distances between them…  collisions probably are infrequent only a few stars should have planets 6/3/2014 21

  22. http://starchild.gsfc.nasa.gov/Images/StarChild/questions/moon_formation.jpghttp://starchild.gsfc.nasa.gov/Images/StarChild/questions/moon_formation.jpg http://www.nightskyinfo.com/sky_highlights/hunters_moon/full_moon_small.jpg Anomoly? The Moon: origin by collision? 6/3/2014 22

  23. http://www.bnsc.gov.uk/assets/channels/education/ae/Uranus_from_Hubble.jpghttp://www.bnsc.gov.uk/assets/channels/education/ae/Uranus_from_Hubble.jpg Anomoly Uranus: rotation/tilted axis by collision 6/3/2014 23

  24. http://www.caffeinenebula.com/nebula04%20(Main)-edit.JPG Solar System Formation: by evolution b. Nebular theory(Laplace 1796) Nebula: clouds of dust & gas in interstellar space - perhaps our solar nebula was 1 light-year in diameter 6/3/2014 24

  25. Solar System Formation: by evolution • these accretion disks (surrounding stars in the process of forming) could be the early stages of planetary formation 6/3/2014 25

  26. Solar System Formation: by evolution Dust disks around some T Tauri stars can be imaged directly (Hubble Space Telescope) 6/3/2014 26

  27. Solar System Formation: by evolution • T Tauri stars are in a highly active phase of their evolution • - have strong solar winds • winds sweep away the gas disk, leave planetesimals and gas giants in its wake 6/3/2014 27

  28. Solar System Formation • Nebular theory (cont’d) • nebular disk grows smaller (over time), spins faster and faster • a () decrease in the size of a rotating mass is balanced by an () increase in its rotational speed… • (to conserve angular momentum)  • () increase in its rotational speed causes nebula’s shape to change • nebula collapses/flattens (in pancake like fashion) to rotation axis 6/3/2014 28

  29. http://www.physics.gla.ac.uk/~kskeldon/PubSci/exhibits/D1/chair.gifhttp://www.physics.gla.ac.uk/~kskeldon/PubSci/exhibits/D1/chair.gif • Angular momentum • the tendancy of a body to keep spinning or moving in a circle • planet’s angular momentum  • (a) mass x (b) velocity (or rotation rate) x (c) distance (or radius2) • So, planets speed up as they approach the sun (conservation of angular momentum) 6/3/2014 29

  30. Conservation of angular momentum… …says that the product of velocity (rotation rate) & distance (radius) must be constant 6/3/2014 30

  31. Nebular contraction • when disk spins as fast as possible, sheds outer edge, leaves ring of matter • as disk contracts further (mass and distance decrease) therefore, velocity increases again, new ring created • - planets form out of ring material -

  32. Nebular contraction • - Consequently, • most stars should have planets • sun should be spinning very rapidly (this is where most of the angular momentum in solar system resides) • planetary orbits should be (relatively) slow (a) not known; (b) and (c) are false 6/3/2014 32

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