Origin of the Solar System Planetary geophysics 2017

The Solar System

Evolution of the material in the Universe

Protoplanetary disk

Protoplanetary disk evolution

Crystalization sequence of solids

Planetesimals and protoplanets Planetesimals are small objects (up to 100 m in diameter) which are formed by dust aggregation and collisions. Protoplanets are larger objects formed by collisions of planetesimals. Thermal metamorphism and differentiation can occur in protoplanets.

Solar element abundances

Evolution of protoplanets Frequent impacts and collisions Growth vs. fragmentation Heating and melting Internal Short-lived radionuclides (60Fe T1/2 = 1.5 Myr, 26Al T1/2 = 0.7 Myr) Crystallization heat Gravitational heat Objects larger that approx. 300 km could have molten interiors External Impacts (in early Solar System evolution maybe more significant than internal sources) Thermal metamorphism Differentiation

Planetesimals and protoplanets

Chronology of the Solar System

Asteroids Asteroids are minor, rocky bodies of our Solar System Size comparison of asteroid Vesta (525 km) and Ceres (950 km) to our Moon (3400 km) Asteroids are minor, rocky bodies of our Solar System Their diameter varies from several meters to hundreds of kilometers (950 km for Ceres) Most of rocky asteroids are orbiting between Mars and Jupiter, forming the main asteroid belt, or in jovian Lagrangian points (Trojan asteroids) Recently, large population of icy bodies was discovered beyond orbit of Neptun (TNO’s) Some of the asteroids have moon or are binary objects Some are orbiting on trajectories approaching or crossing orbit of the Earth (Near Earth Asteroids, NEA) Asteroid Ida (35 km) and its moon Dactyl

Planetary migration – Nice model

Asteroid belt

Asteroid belt

Asteroid belt

Asteroid belt Snow line ~ 150 K

Asteroid belt

How to sample an asteroid Meteorites are fragments of asteroids, moons and planets sent on Earth-crossing trajectories The orbit of most of them originates in the main asteroid belt

Cosmic ray exposure ages in meteorites

History of meteorites Meteorites were long time thought to be of terrestrial (volcanic) or supernatural in origin The oldest observed and recorded fall is the Nogata meteorite (L6 chondrite) that fell in Japan in the year 861 1492 – fall of Ensisheim meteorite was depicted in woodcut (second oldest documented meteorite fall The first book describing meteorites as extraterrestrial rocks is by Ernst Chladni (1794, Über den Ursprung der von Pallas gefundenen und anderer ihr ähnlicher Eisenmassen, und über einige damit in Verbindung stehende Naturerscheinungen)

Basic classification of meteorites Stony meteorites Chondrites Ordinary chondrites Carbonaceous chondrites Enstatite chondrites Achondrites Primitive Differentiated Iron meteorites Stony-iron meteorites

Classification of meteorites

Chondrites Contain chondrules FeO/Fe ratio indicates oxidation conditions C-chondrites are most oxidized (rich in volatiles, hydrothermal alteration on parent bodies), origin in cold environment E-chondrites are most reduced, origin in hot environment

Chondrules Chondrules are 1-3 mm sized spherical objects Bonded together by matrix (like sediment) Rapidly crystalized droplets Origin of chondrules by flash-heating (1000°C) caused by pressure waves in solar nebula Glassy or crystalline (porphyritic, radial, barred, cryptocrystalline, granular)

Chondrites - classification Chondrite group and petrographic type   1 2 3 4 5 6 < 200°C 400°C Aqueous alteration 600°C 700°C > 750°C Thermal metamorphism Chondrules Absent Sparse Abundant, distinct Increasingly indistinct Carbonaceous chondrites CI CM CR CO CV CK R chondrites R Ordinary chondrites LL L H Enstatite chondrites EL EH

Shock scale Stöffler et al. 1991

Shock scale Stöffler et al. 1991

Ordinary chondrites Composed of silicates (olivine, orthopyroxene), metal, sulfides LL most oxidized, E most reduced Various shock level, Common presence of impact melt veins or impact breccias

Carbonaceous chondrites Composed of silicates (olivine, serpentine), oxides, sulfides) Presence of organics, water CAIs CI most primitive (most close to solar element abundances) Some contain abundant FeNi metal (CH, CB) Allende CV

Evolution of meteorite parent bodies

Not that simple… Several contradicting theories exist: External (impact) vs. internal (radioisotope, crystallization, gravity) heating – thus, the onion shell structure may be reversed (more metamorphosed on top)! Hydrothermal alteration of carbonaceos chondrites – individual or heterogeneous layered (even on partly differentiated) parent bodies

Allan Hills 81005 lunar meteorite Achondrites Similar to basaltic, plutonic, or mantle cumulate rocks Primitive – chondritic composition, fine-grained whole-rock melt (Acapulconites, Lodranites, Winonaites) Differentiated – mantial or crustal material of differentiated bodies Breccias often present Origin: asteroids (Angrites, Aubrites, Ureilites, Brachinites), Moon, Mars (SNC), Vesta (HED) Allan Hills 81005 lunar meteorite

Iron and stony-iron meteorites Most likely cores of early protoplanets Structural classification (hexahedrites, octahedrites, ataxites) Chemical classification (groups I-IV) based on Ga, Ge, and IR content Made of FeNi kamacite (low Ni, α-pahse, bcc) and taenite (hign Ni, -phase, fcc) Some show Widmanstätten pattern (exsolution of kamacite and taenite) Stony irons –mixtures of olivine and metal Pallasites are mixtures of iron and olivine (core-mantle boundary) Mesosiderites are breccias with metal clasts

Meteorite chronology

Magnetic susceptibility of meteorites

Stardust and comet Wild 2

Stardust and comet Wild 2 The recovered grains include organic rich compounds as well as high temperature phases. Early Solar System material mixing.

Presolar grains

Oxygen isotopes

Meteoritres and asteroids the scale difference Itokawa asteroid Hayabusa space probe B 550 m Detail of the surface Bjurböle meteorite C D 1 m 5 cm

What to remember Protoplanetary disk and crystallization sequence of solids Planetary migration Asteroids are remains of old planetesimals and protoplanets Collisions and impacts Mixing of material within Solar System Snow line Meteorites bring samples from various regions of asteroid belt Meteorite classification, mineralogy, chemistry