Abundances of elements in solar system. Clue comes from Meteorites (p.15-21) and spectroscopic study on the Sun

Transcription

1 Abundances of elements in solar system Clue comes from Meteorites (p.15-21) and spectroscopic study on the Sun 1

2 Why Study Meteorites? State of early solar system Age of solar system Planetary formation procedure Chemical evolution in solar system Samples of other members (planets, asteroids, comets etc) of solar system Chemical distribution of elements in solar system Information on the internal Earth Hazard for human and other species on Earth 2

3 How often do meteorites come to Earth? 3

4 Where do meteorites come from? Asteroids Comets Mars Moon 4

5 Types of Meteorites [Interplanetary Dust Particles (IDPs)?] Stony Consist of silicate minerals Lunar and Martian meteorites Iron Mostly metallic iron with up to 20% nickel Stony-iron Mixture of silicate and iron 5

6 1. Interplanetary Dust Particles (IDPs) irregularly-shaped IDP collected in the atmosphere Spherical IDP collected on the ocean floor (300 μm across) 6

7 Chondrites 2. Stony Meteorites composed of silicate minerals contain chondrules: solidified droplets of solar nebula unchanged since formation of solar system Achondrites Differentiated chondrites Igneous rocks include Martian meteorites (SNCO) Lunar meteorites 7

8 3. Iron Meteorites Probably represent cores of asteroids Most commonly found meteorites Widmanstätten patterns 8

9 Hoba Iron meteorite, Namibia (largest known) 60 tons 9

10 4. Stony-Iron Meteorites Mesosiderites-breccia of iron-nickel and mantle rock formed by impact Pallasites-represent core-mantle boundary of asteroid 10

11 5. Lunar meteorites (lunaites) 21 lunar meteorites are known. Youngest is 3.1Ga (youngest known phase of flood volcanism on Moon). They are mostly basalt lavas and anorthosite breccias They are very important because they may be samples from different areas than sampled by the Apollo astronauts and the Soviet Luna robots Calcalong Creek meteorite, Australia Lunar basalt. Note large plagioclase feldspar crystals 11

12 6. Martian meteorites (SNCO) S N C O SNCO Meteorites 12

13 Analysis of gases (particularly noble gases) in fluid inclusions in minerals is similar to Martian atmosphere, and suggests that SNC meteorites are derived from Mars 13

14 A bit more on Chondrites The most abundant meteorite falls (~86 %) Very important in understanding early solar system environment Contain Chondrules 14

15 Ordinary Chondrites The Marlow, Oaklahoma, L4 chondrite exhibits sharply defined densely packed chondrules. The chondrules vary greatly in size and shape, many being more ellipsoidal than spherical. They are far from a close packed geometrical arrangement, rather the arrangement here is chance packing. (horizontal view = 15 mm) 15

16 The Baszkowka L5 chondrite frompoland has 20% porosity. Note the large voids in the interior. This meteorite lacks the compaction of most chondrites. This specimen measures about 8 cm in the longest dimension Bjurbole L/LL4 hand specimen. Its extreme friability makes it subject to crumbling. The chondrules frequently fall out of the matrix leaving obvious cavities. The specimen is 5.3 cm in the largest dimension. 16

17 Building of Chondritic Parent Body Experienced Igneous (melting of chondritic precursor followed by crystallization) Sedimentary (accretion of chondrules and matrix material onto a growing homogeneous body) Metamorphic processes (thermal metamorphism occur creating heterogeneous, layered structure) 17

18 Carbonaceous Chondrites The Allende meteorite (one of carbonaceous chondrites) is named for the town in Mexico where it fell on February 8, One of the largest meteorites (total mass = 2 tons). It consists of large, irregularly shaped white inclusions (CAIs) and rounded chondrules in a dark matrix. The inclusions are composed of minerals believed to have condensed at high temperatures from a gas having the composition of the Sun, and their time of formation is older than that of any other known solar system material. 18

19 Carbonaceous Chondrites are believed to be primitive! 19

20 Calcium-Aluminum rich Inclusions (CAIs) A 13.9 g slab of the Axtell CV3.0 chondrite showing a large (9 mm long) CAI in the center. A large (5.5 mm long) fine-grained CAI from an Allende CV3 specimen. Composed of mainly Ca and Al (minerals are highly refractory -> formed under high T -> during early stage in solar system history) Allende contains abundant CAIs (5-10 vol %) The most primitive Solar System material! 20

21 Chronology of Early Solar Events 21

22 Abundances of Elements in Solar system Isotopes (2005) Faure and Mensing 22

23 Key Observations extreme abundance of H and He (more than 99% of all atoms) general decrease in abundance with increasing Z relatively low abundance of some elements (Li, Be, B, Sc) and relatively high of others (Fe, Ni, Pb) greater abundance of even Z elements compared to odd Z elements How can we explain these features? Geochemistry (1996) Brownlow 23

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