Condensation of the Solar NebulaComposition of the Solar Nebula As the protoplanetary disk cools, materials in the disk condensate into planetesimals • The solar nebular contains 98% Hydrogen and Helium (produced in the Big

Bang), and 2% everything else (heavy elements, fusion products inside the stars). • Local thermal environment (Temperature) determines what kind of material

condensates. − Water and most hydrogen compounds have low sublimation temperature, and cannot

exist near the Sun. They exist far away from the Sun.− Metals and rocks have high sublimation temperature, and can form near the Sun.− Frost line lies between the orbit of Mars and Jupiter.

The Four Phases of MatterThere are in fact more than three phases of matter. • Plasma – when the temperature is very high, high energy collision

between atoms will knock the electrons lose, and they are not bounded to the atoms anymore…

Surface of Earth

Surface of the Sun and stars

Core and corona of the Sun and stars

White dwarfs, CMB

What’s wrong with this picture?Red is cold,Blue is hot!

Transition Between Phases

SolidificationSolid Liquid GasLiquidation Evaporation

Condensation

Sublimation: atoms or molecules escape into the gas phase from a solid.

Condensation

Accretion: Formation of the Terrestrial PlanetsAccretion The process by which small ‘seeds’ grew into planets.• Near the Sun, where temperature is high, only metals and rocks can condense.

The small pieces of metals and rocks (the planetesimals) collide and stick together to form larger piece of planetesimals.

• Small pieces of planetesimals can have any kind of shape. • Larger pieces of planetesimals are spherical due to gravity. • Only small planets can be formed due to limited supply of material (~0.6% of

the total materials in the solar nebula). • Gravity of the small terrestrial planets is too weak to capture large amount of

gas. • The gas near the Sun were blown away by solar wind.

Click it!

Solar WindsSolar wind is the constant outflow of gas from the Sun…Evidences of Solar Wind 1. Tails of Comet always point

away from the Sun, indicative of the existence of solar wind.

2. SOHO (SOlar and Heliospheric Observatory) C2 and C3 movies.

Effects of Solar Wind on Planet Formation At certain stage of the planet forming process, Solar winds blow away the gases in the planetary nebula, ending the formation of the planets.

Nebula Capture: Formation of the Jovian Planets• In the regions beyond the frost line, there are abundant supply of solid materials

(ice), which quickly grow in size by accretion. • The large planetesimals attract materials around them gravitationally, forming the

jovian planets in a process similar to the gravitational collapse of the solar nebula (heating, spinning, flattening) to form a small accretion disk.

• Abundant supply of gases allows for the creation of large planets. • However, the jovian planets were not massive enough to trigger nuclear fusion at

their core.

The Results of Selective Condensation…

• Not much light gases were available for the formation of planets near the Sun, but small amount of metals and rocks are available: – The planets close to the Sun are small and rocky…

• There are abundant supply of light gases farther out…– The planets far away from the Sun are big and composed of

gases of hydrogen components…These processes can explain the two types of major planets,

their size differences, locations, and composition.

Origin of Comets and AsteroidsAsteroids • Rocky leftover planetesimals of the inner solar system. • Most of the asteroids are concentrated in the asteroid

belt between the orbit of Mars and Jupiter. • Jupiter’s strong gravity might have disturbed the

formation of a terrestrial planet here. • Jupiter also affects the orbit of these asteroids and sent

them flying out of the solar system, or sent them into a collision cause with other planets.

Comets • Icy leftover planetesimals of the outer solar system.• Comets in between Jupiter and Neptune were ‘bullied’

away from this region, either collide with the big planets, or been sent out to the Kuiper belt or the Oort cloud.

• Comets beyond the orbit of Neptune have time to grow larger, and stay in stable orbit. Pluto may be (the biggest) one of them.

Explaining the Exceptions: Impact and Capture

Evidences of Impact • Comet Shoemaker’s collision with Jupiter • Surface of the Moon and Mercury, • More in Chapter 7…

Effects of Impact • Tilt of the rotation axis of planets

(Venus, Uranus) • Creation of satellites (May be our

moon) • Exchange of materials (Where did

the water on Earth come from if most of the gases were blown away by solar wind after Earth was formed?)

• Catastrophes (Where did all the dinosaurs go?)

Heavy Bombardment There were many impact events during the early stage of the solar system formation process, when there were still many planetesimals floating around.

Where did the moons come from?Giant Impact

• Our moon may have been formed in a giant impact between the Earth and a large planetesimal…

Captured Moons • Phobos & Deimos of Mars may be captured asteroids. • Triton orbits in a direction opposite to Neptune’s rotation

Capture of Comet Shoemaker by Jupiter

The Age of the Solar SystemThrough radioactive dating, we have determine that the age of the solar system is about 4.6 billion years…Potassium-40 (an isotope of Potassium [K19]) decays to Argon-40 by electron capture, turning a proton in its nuclei into neutron (thus changing its chemical properties)…– Potassium-40 exists naturally – Argon is an inert gas that never combine with anything, and did

not condense in the solar nebula…– By determining the relative amount of Potassium-40 to Argon-40

trapped in rock, we can determine the age of rock, assuming that there were no Argon-40 initially…

Radioactive Dating Using K-40

• For every 1.25 billion years, half of the Potassium-40 decay and turn into Argon-40…

• 1.25 billion years is called the half-life of Potassium-40.

The Formation Of Solar System: SimulationsSimulations from www.astronomyplace.com. Check them out!

Orbit in the Solar System, Part 4

History of the Solar System, Part 1

History of the Solar System, Part 2

History of the Solar System, Part 3

Do we Have a Viable Theory?YES!1. We can explain most of the properties of the solar system,

including the exceptions.2. We used only good physics.

Testing Our Theory against other solar system1. Can we find protoplanetary disks (before planets were formed)?2. Can we find other solar system?3. If we do find other solar system, does our theory explain the other

solar system?

Common Characteristics and Exceptions

of the Solar System

We can explain all these in our planetary nebular theory!

Evidences Of Protoplanetary Disks

Do we have any evidence of the existence of planetary nebulae outside of the solar

system?We now have many observational evidences of the existence of the protoplanetary Disks.

Hubble Space Telescope image of the dust disk surrounding Beta Pictoris

Each disk-shaped “blob” is a disk of material orbiting a star…

More Protoplanetary Disks

MAUNA KEA, Hawaii (August 12, 2004) The sharpest image ever taken of a dust disk around another star has revealed structures in the disk which are signs of unseen planets.

Dr. Michael Liu, an astronomer at the University of Hawaii's Institute for Astronomy, has acquired high resolution images of the nearby star AU Microscopii (AU Mic) using the Keck Telescope, the world's largest infrared telescope. At a distance of only 33 light years, AU Mic is the nearest star possessing a visible disk of dust. Such disks are believed to be the birthplaces of planets.

http://www.ifa.hawaii.edu/info/press-releases/Liu0804.html

Are There Other Solar Systems Like Ours?We Haven’t Found Them Yet!But we have abundant evidence of the existence of extrasolar planets!

More Known Planets

What’s wrong with this picture?

Jupiter is way out here, 4.5 AU…

These are all Jupiter-sized planets orbiting very close to the star!

How do we Find The Extrasolar Planets?Doppler Effect Large planets can pull the star to move in a circular motion.Given the measured velocity and periodicity of the star, we can estimate the distance and mass of the planet…

Occultation of the star by orbiting planets Planets passing in front of the star causes the light from the star to drop in intensity (click on the image on the left to go to NASA PlanetQuest page). Direct Imaging Tough! We have not achieved this yet!

An Example of Brown Dwarf (NOT A Planet) Companion to a Sun-Like Star

Astronomers using adaptive optics on the Gemini North and Keck telescopes have taken an image of a brown dwarf orbiting a nearby star similar to the Sun.  The faint companion is separated from its parent star by less than the distance between the Sun and the planet Uranus (~ 15 AU) and is the smallest separation brown dwarf companion seen with direct imaging. 

The research team estimates the mass of the brown dwarf at 55 to 78 times the mass of planet Jupiter.  The discovery raises puzzling questions about how the brown dwarf formed, and it adds to the surprising diversity of extrasolar planetary systems being found with cutting-edge observational techniques…

http://www.ifa.hawaii.edu/users/mliu/Research/hr7672/presswebpage/pressrelease.html

~ 1AU from the Star

It is very difficult to directly image an Earth-like planet very

close to its host star…

Is The Nebular Theory OK?• We have evidences for the existence of protoplanetary disks! • We have found many extrasolar planets…by indirect methods.• We have not found any solar system like ours!

− All the extrasolar planets we found so far are large, Jupiter-sized (or larger) planets.

− All these planets are located very close to the host star, inconsistent with the nebular theory.

Why we don’t find any solar system like ours? May be we just haven’t found them yet!

Possible Explanation Detection LimitLarger planets at close distance to the host stars produce larger Doppler effect and intensity drop…Smaller planets far away from the star produce much smaller effect, and are more difficult to detect.

But, why are these large planets so close to the stars?

According to our planetary nebular theory, large planets can only be formed far away from the host star, behind the frost line, where there are abundant quantities of gases…So, why do we see these large planets so close to the stars?

Possible Explanations?1. May be solar wind did not start or started late in these systems?

Maybe these planets are formed far away from the stars as our planetary nebular theory predicts. But for some reason their host stars didn’t develop a wind, and friction between the planets and the dense planetary gas (which did not get cleared out due to the lack of solar wind) causes the planets to lose their orbital angular momentum and migrate toward the stars.

Summary• We have a viable theory to

explain the formation of our solar system.

• We have evidences that planetary nebulae exist in other star systems.

• However, we have not found a solar system similar to ours outside of our own.Extrasolar planets we found so far do not agree with our theory – The physics of our theory is fundamentally correct, but details of the model may need adjustment…