Introduction to the Solar System

99.9% of the mass is the Sun, 0.1% is Jupiter, Earth is 0.0001%
So the solar system is mostly a star, with a minute amount of metal, rock, ice and frozen gases orbiting around it.
Tiny blobs of condensed rock and metal orbiting close in
Massive planet, Jupiter, 1 billion km from the star
Then a few large icy planets
Then a halo of smaller ice balls part way out to the stars

clusters of galaxies, 10-100 billion of them in the universe

Our place -- a star in one of the spiral arms, where there is gas and 'dust'
Each star is a pinpoint where the gas and dust condensed, or collapsed, within the huge cloud that made out galaxy

This is a region where a huge interstellar cloud is dramatically shrinking into pinpoints that form stars
This is what we see with large-Earth based telescopes. The telescopes we have at SBO can do this, with CCD imaging. We'll try to use them tonight

This is a mosaic of 45 images from the Hubble Space Telescope
Large telescope in space with no turbulent air (or heat waves) to blur the image
Where it is brightest, you can see 4 bright stars, brand-new, Trapezium
The stars are so bright and brand new that they illuminate the whole nebula
Nebula--cloud of gas and dust in space (after cloud, like they look)
Numerous other new stars (~700) of varying sizes
The stars form when local regions of the gas start to collapse due to gravity, a process called Jean's collapse
As the regions of gas and dust collapse, they get squeezed. Eventually, hydrogen atoms are squeezed together to create helium.
This nuclear reaction produces a tremendous amount of energy, in the say way a hydrogen bomb produces energy.
But this energy is under so much pressure from the gravity of the gas itself that it doesn't blow apart
The gas collapses into a sphere, until the energy from gravity is balanced by the energy from the burning hydrogen. Collapse that is slowed down by the pressure is called Helmholtz collapse
The star begins to burn and illuminate its surroundings
When the star ignites, it often pushes the lightest gases from around it out violently, creating a strong solar wind
The wind smacks into the interstellar gas, creating shock waves that we can see on the slide

But what happens to all the stuff around the star that didn't get squeezed enough to burn?
As the cloud contracts under gravity, it begins to spin like a skater bringing in his arms as he spins
The region of gas and dust around the star spins with it, glued to the star through gravity and magnetism --solar nebula
A flattened disk forms around the star, with the star bulging in the middle
As the disk cools, and before all the light gases get blown away by the strong solar wind, grains of stuff begin to condense out, like ice in a cooling pond
As it cools below 1300 C, metals condense out as tiny little filings
PLOT: distance vs. Temperature in the Solar NebulaAs it cools below 1000 C, rocky materials, called silicates, condense out as grains
As it cools below 0 C, water ice condenses
As it cools below -100 C, CO2, CH4 and N2, frozen gases, begin to condense out, way at the edge of the solar system
This process is called the condensation sequence, and is fundamental to understanding the origin of the solar system

We should get a disk, around the young star, with grains of metal, silicate, ice and frozen gases.
Until 4 years ago, this was all pure theory, pieced together from the evidence our spacecraft gave us from exploring and measuring the objects in the inner and outer solar system. Then came the Hubble Space Telescope.

We look deep into the star forming regions of the Orion Nebula, where stars have just formed, and we see dark regions around stars! Sometimes you can see the edge of the disk lit up by the bright new star.

Here are 4 of the dark stellar disks, viewed at different angles. They are between 2 and 8 times the size of our solar system. These stars are only 1 My old, and about the same size as our sun. The dark part is dust that obscures the glowing background

This is what one looks like at the highest possible resolution of the Hubble Space Telescope. It is an unmistakable disk around a star. It is a solar system in the making. There are at least 150 of these in the Orion Nebula, right now, and the Orion Nebula is only one of 1000's of giant gas and dust clouds in the spiral arms of our galaxy.

Adjacent grains have low relative velocity, and when they bump into each other, they don't bump hard
Due to 'static cling' or electrostatic forces, they stick together
When they start sticking, they get pebble sized, then boulder sized, and pretty soon they have enough gravity to pull in even more grains -- accretion
When they have accreted to 100 m to 100 km, they are called planetesimals
Planetesimals, in turn, crash into each other, and when they get into big enough lumps, they start melting--protoplanets
Regions are cleared away in sections, giving the spacing between planets
This leads to a certain spacing of planets -- each one is about twice as far out as the one closer in--Bode's Rule
DRAW SOLAR SYSTEM, with DISTANCES IN AU
Astronomical Unit -- distance between Earth and Sun

Inner solar system -- Mercury from swept up grains and planetesimals of metal and rock
Earth, Venus, Mars, swept up grains and planetesimals of rock, metal and ice
Jupiter and Saturn -- swept up rock, ice until they reached a size of 15 Earth masses
There was still the stuff the sun was made of around -- H2 and He, in the solar nebula
At 15 X Earth mass, there was enough gravity in proto-Jupiter and proto-Saturn to begin capturing large amounts of the original solar nebula
H2 and He added until Jupiter became 1000 Earth masses, Saturn a little less
Uranus and Neptune -- cores of ices and frozen gases that got big enough to do some capturing of the solar nebula
Small balls of ice and frozen gas formed all around Jupiter, Saturn, Uranus and Neptune, and beyond -- comets, billions of them
Because of the gravity of the giant planets, the icy balls and rock planetesimals left over were scattered all over the solar system
Most of the icy bodies near Uranus and Neptune were ejected out into a spherical halo that goes 1/4 of the way out to Alpha Centauri, the nearest star -- Oort cloud, 10 billion comets
Some were scattered inwards, contributing to the Earth's oceans and Mars' polar caps.
A record of this time is shown on the oldest surfaces of the planets--surfaces that have not been erased by erosion or tectonics (folding of crust) -- Moon and Mercury, parts of Mars
Over time, planetesimals either hit the planets, crashed into the sun, got ejected out of the solar system, or ended up outside Neptune. They eventually cleared away
Some got stuck where a planet couldn't form, due to the gravity of Jupiter -- asteroids
Some were already formed way beyond Neptune, and stayed there millions? Kuiper Belt
Some say that Pluto is the biggest of these ice balls that formed outside of Neptune, and got caught by its gravity -- large comet

Bits of broken asteroids that fall to earth. We still get 1/2 ton a day. Small ones burn up
There are rocky ones, metal ones, and not-very-dense ones, called carbonaceous chondrites. They have a lot of the lightest elements, C, H, O, N--the molecules of life
They also have bits of condensed metals, the first things to condense out of the solar nebula Calcium-Aluminum Inclusions (CAIs)

Gives a personal account of how astronomers go about their work. In this case, the search for planets around other stars. Also discusses the Voyager missions to the Outer Planets

6/12/96