Solar System Formation And the Stuff that was Left Over

Things we need to explain The similarities in the motions and orbits of the objects in the solar system Dichotomy in planetary morphology and composition Asteroids and comets Peculiarities

Orbital Patterns All planets orbit the sun in the same direction Orbits nearly circular and in same plane Nearly all rotate the same direction as sun Satellites have properties similar to their host planets

Morphology Dichotomy Located in inner solar system Small and dense Rocks and metals Few satellites No rings Located in outer solar system Large and low density Lots of H compounds Lots of satellites Rings Terrestrial Planets Jovian Planets

Peculiarities Uranus rotates on its side Venus rotates opposite to its orbital motion Earth has one of the largest satellites in inner solar system –Other inner planets don’t have satellites or very small ones

What theory can explain all this?

The Nebular Theory

Orbital Motions Heating – because of conservation of energy, as nebula contracts, it heats up Spinning – because of conservation of angular momentum, as nebula contracts, it spins faster and faster Flattening – due to collisions

Making Planets Start with some seed Accretion – the process of more and more material being added to the seed Gravity attracts more stuff –Inside frost line: all heavy elements –Outside frost line: Hydrogen compounds can condense

Clearing out the Nebula Young sun lights up and starts pouring out radiation and particles Radiation and solar wind blow away the rest of the H and He Clearing out the gas stops the planet from accreting more material Planets are now stuck with what they’ve got

Peculiarities

When did the Solar System Form? Radiometric dating shows us the solar system is about 4.5 billion years old Look at ratios of radioactive isotopes Half life – the length of time required for half of the material to decay

Asteroids, Meteors, and Comets Oh My!

What’s the Difference? Asteroid –Rocky leftover planetesimals that never made it into a planet Meteor –Flash of light in Earth’s atmosphere –(The weather person is a meteorologist) Comet –Similar to asteroids but made of ice –Where were they formed Dwarf Planet –Big enough to be round –Not big enough to clear its orbit

Asteroids Small rocky planetesimals Not big enough to have enough gravity to make them round Craters show us that they have histories similar to planets

Asteroid Belt Belt between Mars and Jupiter where most asteroids live Why is it there?

Asteroid Belt Orbital Resonances with Jupiter –Creates Kirkwood gaps in belt –Prevented asteroids from ever coming together and forming a planet

Meteors Meteor – flash of light caused by something entering Earth’s atmosphere Meteoroid – the object in Earth’s atmosphere Meteorite – such objects once they have reached the ground

Meteorites Primitive Meteorites –Unchanged since the formation of the solar system Processed Meteorites –From the core of a shattered asteroid –Often mostly Fe

Comets

Structure

Interior Nucleus –Main chunk of ice from which the comet is made Coma –Cloud of gas around nucleus caused by sun’s heating of the ice

A Tale of Two Tails Plasma Tail –UV light from sun ionizes gas in coma –Solar wind pushes ions away from sun Dust Tail –Dust-sized particles unaffected by solar wind –Pushed away by radiation pressure

Origins Oort Cloud –Goes out to 50,000 AU –Contains trillions of comets Kuiper Belt –30-50 AU Heavy bombardment Comets get flung way out by big things like Jupiter

Kuiper Belt Objects

Fate Ice binds comet together When all the ice is melted away, the comet might disintegrate

Fate

Tunguska Video

Exoplanets

Detection Direct Detection – Images of the planet itself Indirect Detection – precise measurements of the host star that tell us a planet must be orbiting it

Direct Detection Extremely difficult –Star is usually too bright –Need outstanding angular resolution Fomalhaut and its planet seen by HST

Indirect Methods

Gravitational Wobble: Astrometric Technique

Doppler Technique

Transits Planet travels in front of star, blocking some of stars light, which we can measure Movie