Origin of the Solar System and Solar System Debris 1
Debris comets meteoroids asteroids gas dust 2
Asteroids irregular, rocky hunks small in mass and size Ceres - largest, 1000 km in diameter (1/3 Moon) 3
Asteroid Belt 2.8 AU from the Sun, between Mars and Jupiter some with highly eccentric orbits, e.g. Icarus, goes inside the orbit of Mercury 5500 asteroids discovered so far 4
A Typical Asteroid fluctuates in brightness => tumbling, irregular in shape cratered surfaces, often rough and pitted lose chunks in collisions Toutatis - two orbiting each other 5
Categories of Asteroids S type (stony) relatively bright stony silicate materials C type (carbon) darker contains carbon compounds M type (metallic) brighter than C, darker than S metallic substances 6
Comets - Heralds of Disaster first seen as a bright blob later grows brighter and sprouts a tail as it nears the Sun 7
Comets coma: bright head of the comet may reach a million km diameter nucleus: small central core, about 10 km tail: material in the comet is heated by the Sun and vaporizes, can be millions of km s long 8
Two Tails! gas tail: ion tail emission lines ionized gas plasma carbon monoxide (CO) carbon dioxide (CO 2 ) molecular nitrogen (N 2 ) magnetic fields interact with plasma giving the comet a glow 9
dust tail: spectrum of sunlight reflected by the dust radiation pressure pushes dust out of the coma points downward from the ion tail 10
Dirty Snowball Model Nucleus: solid, compact body frozen ices (water, methane, ammonia) embedded in rocky material Coma: nears the Sun, icy material vaporizes, forming the coma Tail: continual vaporizing enlarges the coma and forms the tail 11
Periodic Comets make regular passes near the Sun follow Kepler s Laws have elliptical orbits short period: long period: orbit in same directions as the planets, less eccentric highly eccentric orbits, cut through plane of Solar System 12
Oort Cloud a reservoir of comets out beyond Pluto, beyond the Kuiper Belt (belt of icy objects) average semi-major axis is 50,000 AU, period of 10 million years, eccentricity close to 1 travel very slowly, spend a lot of time far out in their orbits 13
Wonder of It All How did they get out there in the first place? 14
Meteors and Meteoroids meteoroid: meteor: meteorite: name for particles and such before entering Earth s atmosphere solid particle that vaporizes in Earth s atmosphere particles large enough to survive and land on Earth 15
Origins of Meteoroids dust and ice flaked from comets 99% comes from comets follow orbits of original comets meteor showers: many meteors in a short period of time 16
irons stones Types of Meteoroids 90% iron, 9% nickel high density, melted appearance low density silicates similar to Earth s crust chondrules - silicate spheres carbonaceous chondrites: chondrules embedded in material containing a lot of carbon 17
stony iron: crossbreed between stones and irons meteorites - come from asteroids rather than from comets have enough density to make it through our atmosphere Identify a meteorite: etch a polished surface with acid and look for Widmanstatten figures They were originally inside a larger body and could cool slowly. 18
C type asteroid S type asteroid M type asteroid carbonaceous chondrite stony meteorite iron meteorites probable that the parent bodies were first things to form in the Solar System - ages will directly indicate the age of Solar System 19
Solar System Chemically: Sun mostly gaseous with some icy/rocky material as gases Terrestrial planets & asteroids rocky, metallic Jupiter, Saturn mostly gaseous Uranus, Neptune, Pluto, Charon, comets mostly icy 20
Dynamically planets revolve counterclockwise Sun rotates counterclockwise major planets have orbits only slightly inclined with plane of Sun exceptions: Pluto and Mercury planets move in orbits that are nearly circular (low eccentricity) exceptions: Pluto, Mercury 21
planets rotate counterclockwise (same direction as orbital motion exception: Venus, Uranus, Pluto planets orbital distances follow a regular spacing (sort of) - about twice as one before most satellites revolve in same direction as parent planet rotates and lie close to equatorial plane some satellites orbital distance follows a regular spacing rule 22
planets together contain more angular momentum than the Sun (99.5% vs 0.5%) long period comets - come in from all angles and directions short period comets, planets, satellites, asteroids - coplanar orbits all Jovian planets have rings 23
Nebular Model Sun and planets form from a cloud of interstellar material Sun forms in the center of flattened cloud Planets grow from the disk of the cloud Solar System is basically flat with the Sun in the middle. 24
Conservation of Angular Momentum once something starts spinning, it will continue unless acted on by an external influence angular momentum: tendency to keep spinning angular momentum depends on the mass and on how that mass is spread out Any time a body contracts (gets smaller), it spins faster in order to conserve angular momentum. 25
Imagine, a large cloud of gas and dust, slowly spinning. It starts to shrink, pulling in on itself with its own gravity. What happens? It spins even faster!! And eventually it collapses along the rotation axis. a flat disk with a fat center! 26
Nice model.. one problem... Angular momentum is not as expected. Sun 99% mass 1% ang. momentum Planets 1% mass 99% ang. momentum Sun should be spinning very rapidly! 27
gravitational contraction: a mass pulling itself together gets hotter gravitational potential energy kinetic energy (heat energy) As the cloud contracts, it gets hotter. 28
Stages of Evolution formation of nebula out of which the planets and Sun originate formation of original planetary debris evolution of planets dissipation of leftover gas and dust 29
Planetary Formation grains collide & accrete to form larger, pebble-sized objects pebbles accumulate into planetesimals by gravitational contraction composed of whatever is handy planetesimals gather into larger bodies takes tens of thousands of years clear out a space in the nebula protoplants - process takes 100 million years 30
Condensation Sequence temperature determines what materials condense below 2000 K, grains of terrestrial material condense below 273 K, grains of terrestrial and icy materials condense 31
Different distances from the Sun, different temperatures allow different materials to condense and form into grains. How LOW the temperature gets determines what materials. Leftover planetesimals bombard the new planets surfaces causing craters. 32
Planets become differentiated. Some rocky, metallic planetesimals end up as asteroids. Icy ones become comet nuclei. 33