Transcript Condensation of the Solar Nebula

Condensation of the Solar Nebula
Composition 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.
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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 Matter
There 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…
Core and corona of the Sun
and stars
Surface of the Sun and
stars
Surface of Earth
White dwarfs, CMB
What’s wrong
with this picture?
Red is cold,
Blue is hot!
Transition Between Phases
Liquidation
Solid Solidification
Liquid
Evaporation
Condensation Gas
Condensation
Sublimation: atoms or
molecules escape into the
gas phase from a solid.
Accretion: Formation of the Terrestrial Planets
Accretion 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 Winds
Solar 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
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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 Asteroids
Asteroids
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Rocky leftover planetesimals of the inner solar system.
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Most of the asteroids are concentrated in the asteroid
belt between the orbit of Mars and Jupiter.
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Jupiter’s strong gravity might have disturbed the
formation of a terrestrial planet here.
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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.
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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
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.
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?)
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 System
Through 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 K40
• For every 1.25 billion
years, half of the
Potassium-40 decay
and turn into Argon40…
• 1.25 billion years is
called the half-life of
Potassium-40.
The Formation Of Solar System: Simulations
Simulations from www.astronomyplace.com. Check them out!
History of
the Solar
System,
Part 1
History of
the Solar
System,
Part 3
History of
the Solar
System,
Part 2
Orbit in the
Solar
System,
Part 4
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 system
1. 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!
Do we have any evidence of the existence of
planetary nebulae outside of the solar
system?
Evidences Of Protoplanetary Disks
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?
These are all Jupitersized planets orbiting
very close to the star!
Jupiter is way out here, 4.5 AU…
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
http://www.ifa.hawaii.edu/users/mliu/Research/hr7672/presswebpage/pressrelease.html
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…
It is very difficult to directly
image an Earth-like planet very
close to its host star…
~ 1AU from
the Star
Is The Nebular Theory OK?
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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 Limit
Larger 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…