(4) Meteorites: Remnants of Creation

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Natalie Oliver
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1 (4) Meteorites: Remnants of Creation Meteoroid: small piece of debris in space Meteor: space debris heated by friction as it plunges into the Earth s atmosphere Meteorite: Space debris that has reached the ground

2 Two basic properties of the Solar System Chemical composition. Fractionation: chemical sorting that results, for example, in different planets being composed of different materials All planets have nearly circular orbits that lie roughly in the same plane, and all revolve in the same direction around the sun.

3 Formation and Condensation of the Solar Nebula Stars form out of clouds of molecular gas & dust Collapse occurs when the gas is dense enough to collapse under its own weight Central parts of collapsing cloud become heated, & the shrinking nebulae begin to spin faster Angular Momentum = Mass x Velocity x Radius Example: ice skater pulling in their arms as they spin Results center becomes star spinning disk ultimately gives rise to planets

4 Star-Forming Region in the Orion Constellation

5 Disk Evolution Temperature gradient develops in the disk outer disk cools inner disk is heated by proto-sun Grains, whose composition depends on the local temperature, begin to condense stick together initially, building up planetesimals planetesimals attract each other gravitionally (a process called accretion) Protoplanets form, sweeping up grains in their path As protoplanets grow in size, fragmentation becomes important for the production of meteoroids & asteroids (as well as for heating the interior of the planets)

6 Artist s conception of collapsing stellar disk

7 An example of a disk: β Pictoris

8 Central star has been blocked by a Coronagraph Another Example

9 Circumstellar disks (optical)

10 More Examples

11 Solar System formation time-line

12 (Solar System Formation Video)

13 The Importance of Meteorites Remnants from the formation of the solar system Provide clues to their Parent Bodies Easily accessible

14 Classification 1) Iron: nearly pure metallic (nickel-iron) of high density (7 g / cm 3 ) 2) Stones: like terrestrial rocks (silicates, carbon compounds, water) 3) Stony Irons: mixture of 1) & 2)

15 Classification (cont) Primitive meteorites: meteorites for which little chemical evolution has occurred since the formation of the solar system (stones) Differentiated (or igneous) meteorites: meteorites that have experienced significant chemical chance since their formation (i.e., solidified from molten state; iron/stony irons) Another term commonly used: Breccias: fragmented and recemented rocks.

16 Locating Meteorites Qu: Where is a good place to find meteorites? An: The Antarctic Why? 1) Relatively easy to find in ice 2) The ice protects the meteorite from additional weathering

18 Name of the Meteorite = Location it is found

19 Age-Dating Meteorites Solidification Age: Time since the material became solid Gas Retention Age: A measure of the age of a rock, defined in terms of its ability to retain radioactive argon (which is the daughter product of potassium)

20 Half-Life Half-Life: Given a quantity of material, the half-life is the time which half the material will have decayed into the daughter product Examples - Radioactive Decay U-238 (92p +,146n) Pb-206 (82p +,124n) + (10p +,22n) K-40 (19p +,21n) Ar-40 (18p +,22n) The Decay Rates U billion years K billion years

21 Radioactive decay of Potassium-40 to Argon-40

22 Radioactive Decay Mathematically, this is written as Initial amount of Parent product N = N 0 e Lt Present amount L is a constant that can be derived as follows, N = 0.5 N 0 = N 0 e L t hl I.e, at time = half-life time Age of rock L = t hl ln 2 t hl t = ln ln 2 N N 0 Fraction of Parent product left

23 Summary of Meteorites Age-dating of meteorites puts the solar system formation age at 4.5 billion years ago The parent bodies of meteorites appear to be primarily asteroids (with diameters of a few 100 km), though some clearly come from the moon and Mars. Little chemical processing of primitive meteorites Crystal patterns of differentiated meteorites basalt meteorites from lunar surfaces ( billion years old SNC meteorites which contain material associated with very recent volcanism (1.4 billion years ago i.e., from Mars) Reconstruction of the orbits of a few meteorites indicates that they may have originated in the asteroid belt

Our Planetary System & the Formation of the Solar System

Our Planetary System & the Formation of the Solar System Chapters 7 & 8 Comparative Planetology We learn about the planets by comparing them and assessing their similarities and differences Similarities