How did the Solar System form? 3. What are the broad general characteristics or physical features of our Solar System and how do they illuminate Solar System formation?
How did the Solar System form? 4. How did the terrestrial planets form and why is the Solar System differentiated?
How did the Solar System form: Differentiation? • The Solar System is differentiated. This means that it is broken up into different parts, these parts are two types of planets (and ice-rocky bodies). We need a theory to account for this fact. • Terrestrial-like or Inner Planets • Jovian-like or Gas Giants • Pluto-like bodies. • What Solar System feature separates these objects?
How did the Solar System form: Asteroids? • Asteroid = a rocky body that likely originated from the asteroid belt and is < 1000 km (although most are ~1 km) in diameter. They are minor planets. • They are the remains of the formation of Earth-like planets.
How did the Solar System form: Asteroids? • On January 1st 1801, Giuseppe Piazzi discovered an object which he thought was a new comet. • Its orbit, however, was more like a small planet. • He named the object Ceres, after the Sicilian goddess of grain. • Thus the first asteroid was discovered.
How did the Solar System form: Asteroid Location? • The asteroid belt is located between Mars and Jupiter. • It is approximately 2-3 AU from our star, known as the Sun.
How did the Solar System form: Meteorites? • Meteorites are pieces of asteroids that travel through our solar system and land on Earth. • Before they land they are termed meteors. • They are rocks from space!
How did …: Differentiated Meteorites? • Iron meteorites - • These are the cores of minor planets. • They are mainly composed of Fe and Ni. • They comprise 7% of all the meteorites found on Earth.
How did …: Differentiated Meteorites? • Stony-iron meteorites. • These are the core-mantle boundaries of minor planets. • Such rocks are composed of Fe-Ni metal and silicates, usually the minerals olivine or pyroxene. • They compose 1% of all the meteorites found on this planet.
How did …: Differentiated Meteorites? • Achondrites (a type of Stony meteorite). • Such rocks are similar to magma and lava on Earth. They may have come from mantle and crust areas of minor planets. • They may also be from other planets such as Mars or from the Moon. • They compose 8% of all the meteorites found on this planet.
How did …: Differentiated Bodies? • This is the process of becoming different. A differentiated body (planet, moon, asteroid, etc.) is one that was heated internally and melted. Upon heating material then separates due to differences in the density. • The Earth, Venus, Mars, Mercury, Vesta, and the Moon are examples of differentiated bodies. • Thus, differentiated meteorites have been through a planetary-type melting process.
How did the Solar System Form: Undifferentiated Meteorites? • Chondrites (another type of Stony meteorite). • No rocks on Earth are in any way like these rocks. • They have not been through a differentiation process. They are undifferentiated. • They compose 84% of all the meteorites found on this planet. • They are fossils or the physical remains of the formation of Terrestrial planets.
How did… : What are the components of chondrites? • Chondrules • Calcium-rich, aluminum-rich inclusions • Circumstellar grains • Matrix
How did…: Why should you care about chondrites? • They are 4.556 billion years old. • They are the oldest rocks in our collection. • Tell the story of the earliest time of our solar system’s formation. They should not exist by accepted astrophysical models for solar system formation. • Are what the Earth-like planets were made from. • Contain mineral grains from other stars.
How did… : Chondrules • Chondrules are the most abundant component of chondrites. • Chondros, = grain or seed (Rose, 1864) • Chondrules are mm to cm-size spherical igneous rocks composed mainly of olivine, pyroxene, and glass. They are igneous rocks, rocks that have been melted in our nebula. • They are the building blocks of Earth-like planets.
How did… : Chondrules and Their Formation. • Because chondrules are igneous, they were melted. • Because they are not predicted to exist, it is critical to determine what formed these objects. • Because most meteorites are chondrites and thus most asteroids are likely chondrites, processing was extensive. Thus some mechanism operated that processed rock-forming materials by melting BEFORE the formation of the terrestrial-like planets.
How did… : Chondrules and Their Formation. • What mechanisms are hypothesized to produce chondrules within our protoplanetary disk? • Two general classes of hypotheses: • I. Observed or known to have occurred • 1. Link their formation to our YSO. • 2. Collisions • II. Hypothesized to have occurred • 1. Nebular Shock Waves • Some other process
How did the Solar System Form: Terrestrial Planets. • The theory, as discussed by astronomy and astrophysics, states that planets within the inner solar system formed in three major stages. • Stage I • 1. Dust grains acted as nuclei formation of matter, or meter-sized rocks. • 2. These meter-sized rocks accreted and collided to form kilometer-sized rocks (asteroids). • 3. These objects then formed planetesimals, small moon-sized objects.
How did the Solar System Form: Terrestrial Planets. • The theory, as discussed by geologists, states that planets also formed in three major stages, but that Stage I has four parts: • 1. Dust grains acted as nuclei formation of millimeter-sized dust-balls that were melted and produced chondrules and CAI. • 2. Chondrules and CAIs then accreted to form meter-sized objects. • 3. Meter-sized objects then formed kilometer-sized objects. • 4. Kilometer-sized objects then formed planetesimals. • Melting and differentiation occurs here
How did the Solar System Form: Terrestrial Planets. • Stage II: • Planetesimals then collide and merge due to gravitational forces between them. The total number of these types of bodies decrease and larger bodies known as protoplanets are produced.
How did the Solar System Form: Terrestrial Planets. • Stage III: The process of accretion of planetesimals also leads to fragmentation of bodies and heavy bombardment occurs. • The fragments are swept up by protoplanets. • These objects then become planets.
How did the Solar System Form: Terrestrial Planets. • After accretion we are left with a solar system. The condensation theory helps account for the differentiation of the solar system into terrestrial-like and Jovian-like planets. • A major issue if not the major issue - Temperature!
How did the Solar System Form: Jovian Planets. • Formation of the Jovian or gas-giant planets is a little less clear with a weaker consensus among scientists as to a party-line theory. • 1. These planets simply grew large or massive enough that their gravitational fields pulled large masses of gas to their “cores”. • 2. They formed from instabilities in the cool outer regions of the solar nebula, mimicking small scale nebular models. • As of July 2003, this last hypothesis is given more weight.
How did the Solar System Form: No more gas and dust. • Where did all the gas go? • The major hypothesis states that gas, which did not fall into the sun or form into planets, was both blown off and reacted away by solar winds and solar radiation during the highly active stage of our star known as the T Tauri phase.
How did the Solar System Form: No more gas and dust. • Where did all the dust go? • Simple, into the Sun or planets! Effective processing.
An Important Point of Interpretation • Standard textbooks form Terrestrial planets like this: • Dust to m-sized objects to km-sized objects to Moon-sized objects to Planets! • But that’s wrong. Why? No chondrules! • Dust to mm-sized objects then zap then m-sized objects, etc. • REMEMBER THIS POINT