5' The Planets orbital distance from the Sun follows a regular spacing'

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5. The Planets orbital distance from the Sun
follows a regular spacing.
Titius-Bode rule
Write down 0, 3, 6, 12, each number, after the
first, being double the previous value. Add 4 to
each and divide by 10.
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Titius-Bode Rule and Distance
Distance AU
T-B distance AU
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A packed Solar System?
The solar system may be as densely packed as
possible. There do not appear to be any orbits
stable over the lifetime of the solar system
between the current planets.
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6. Most satellites revolve in the same direction
as their parent planets rotation and lie close
to their parent planets equatorial plane
An exception is Neptunes Triton
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Discussion
How would you explain this observation with our
formation theory of the Solar System?
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7. The Sun contains 99.8 of the solar systems
mass but only 0.5 of the angular momentum
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Discussion
If the Sun formed from a single spherical
rotating cloud, wouldnt you expect that all the
pieces would have the same angular momentum as
the original cloud? What does this mean for the
evolution of the Solar System after formation?
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Discussion
Either the Suns rotation rate has slowed over
time, or the planets have been spun up in their
orbits. How could we decide between these two
possibilities?
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Slowing the Suns rotation
Magnetic breaking The Suns magnetic field
might interact with the early solar nebula to
slow the Suns rotation. Strong solar winds
early in the history of the Sun might have
carried the extra angular momentum away.
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8. Long period comets come from all directions
and angles in contrast to the coplanar orbits of
the planets.
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Discussion
If the long period comets can have any
inclination, what does this tell you about their
distribution around the Sun?
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9. All the Jovian planets have rings and a large
number of moons
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10. All the Jovian planets have a core of
icy/rocky material with between 10-15 times the
mass of the Earth
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Discussion
Why do you think these cores are all about the
same size?
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Jovian Planets
Once at protoplanet reaches a mass of about 10
times that of the Earth, it can capture large
amounts of gas directly from the solar nebular,
becoming a Jovian planet.
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Discussion
Why do you think Uranus and Neptune didnt get as
big as Jupiter and Saturn?
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11. Most solid planetary surfaces are heavily
cratered
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Meteor Crater (1.2 km)
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Arizona from the Shuttle
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12. All planets are enriched with high Z elements
in comparison with the solar abundances
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The Planetesimal Hypothesis
Fluffy dust grains condensing out of the solar
nebula stick together as a result of low-speed
collisions, building up to small bodies called
planetesimals.
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Protoplanets
As the protoplanets grow by accretion of
planetesimals, their gravity increases spurring
more accretion.
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Solar nebula composition
We expect that the solar nebula from which the
Sun formed, had the same composition as the
current solar surface. 98 hydrogen and
helium 1.4 hydrogen compounds CH4, NH3,
H2O 0.4 silicate rocks 0.2 metals
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Discussion
If the planets and Sun all formed from the same
nebula, why dont all the planets and the Sun of
the same chemical composition? The outer
planets have about the same composition as the
Sun but the terrestrial planets do not. Why?
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Extra Solar planets
Most extra-solar planets are Jupiter-like planets
which lie very close to their star.
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Planetary Migration?
Maybe these planets formed beyond the frost-line,
but due to friction with the remaining gas and
dust lost orbital speed and slowly spiraled in
toward the star.
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The Sun
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Solar Data
Radius 109 Earth radii Mass 333,000 Earth
masses Composition 74 hydrogen 25
helium Mean density 1.41 g/cm3 Luminosity 3.86
? 1026 Watts
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The Sun as a big cosmic light bulb
Suppose every human being on Earth turned on
1000, 100-watt light bulbs. With about 6
billion people this would only be 6 ? 1014
watts. We would need 670 billion more Earths
doing the same thing to equal the energy output
of the Sun.
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Discussion
Why does the Sun shine?
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Discussion
How do you know the Sun is hot?
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Infrared radiation
The Sun feels warm because of the infrared
radiation it emits. Anaxagoras (500 428
B.C.E.) believed the Sun was a very hot, glowing
rock about the size of Massachusetts.
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Discussion
But if the Sun were simply some cooling ember,
what does this imply about the past condition of
the Sun?
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No cooling ember
At the rate that the Sun is emitting energy, the
Sun must have been much hotter just a few hundred
years earlier, making life on Earth impossible.
The Sun must have an energy source a way of
generating its own heat.
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The age of the Sun
Sedimentary rocks on Earth which were deposited
in liquid water are 3.8 billion years old.
Rocks containing fossils are 3.5 billion years
old. The Sun must have been shining for at least
this long.
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What energy source can keep the Sun hot for 3.8
billion years?
Burning coal Sun would last 10,000 years
Kelvin-Helmholtz contraction if the Suns heat
were generated from contraction of the Suns
mass, it would shine for only 25 million years.
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E m c2
Energy equals the mass times the speed of light
squared.
Matter is a form of frozen energy.
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The Sun is huge!
A little bit of matter can be turned into a large
amount of energy. If the Suns mass could be
converted to energy it could shine for hundreds
of billions of years. The Sun needs to convert
4.3 million tons of matter to energy every
second.
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The Suns Mass is Converted to Energy
4 hydrogen atoms have a mass of 6.693 ? 10-27 kg
1 helium atom has a mass of 6.645 ? 10-27
kg Thus, 0.048 ? 10-27 kg are converted to
energy.
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Thermonuclear Fusion
The Sun fuses 4 hydrogen atoms together to
produce 1 helium atom releasing energy. In the
Sun about 600 million tons of hydrogen is
converted to helium per second.