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Intro to Solar System Origins of the Solar System 1

Origin of the Solar System

and Solar System Debris


Debris

• comets

• meteoroids

• asteroids

• gas

• dust


Asteroids

irregular, rocky hunks

small in mass and size

Ceres - largest, 1000 km in diameter

(1/3 Moon)


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


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


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


Comets - Heralds of Disaster

first seen as a bright blob

later grows brighter and

sprouts a tail as it nears

the Sun


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


Two Tails!

gas tail: ion tail

emission lines

ionized gas

plasma

carbon monoxide (CO)

carbon dioxide (CO2)

molecular nitrogen (N2)

magnetic fields interact with plasma

giving the comet a glow


dust tail: spectrum of sunlight

reflected by the dust

radiation pressure pushes dust

out of the coma

points downward from the ion tail


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


Periodic Comets

• make regular passes near the Sun

• follow Kepler’s Laws

• have elliptical orbits

short period: orbit in same directions

as the planets, less eccentric

long period: highly eccentric orbits, cut

through plane of Solar System


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


Wonder of It All

How did they get out there in the first place?


Meteors and Meteoroids

meteoroid: name for particles and such

before entering Earth’s

atmosphere

meteor: solid particle that vaporizes

in Earth’s atmosphere

meteorite: particles large enough to

survive and land on Earth


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


Types of Meteoroids

• irons 90% iron, 9% nickel

high density, melted appearance

• stones low density silicates similar to

Earth’s crust

chondrules - silicate spheres

carbonaceous chondrites:

chondrules embedded in material

containing a lot of carbon


• 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.


C type asteroid carbonaceous

chondrite

S type asteroid stony meteorite

M type asteroid 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


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


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


• 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


• 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


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.


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.


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 !


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!


gravitational contraction:

a mass pulling itself together gets hotter

gravitational potential energy

kinetic energy (heat energy)

As the cloud contracts, it gets hotter.


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


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


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


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.


Planets become differentiated.

Some rocky, metallic planetesimals end up

as asteroids. Icy ones become comet nuclei.

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