Small Objects in the Solar System' The Sun'

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Lecture 35

• Small Objects in the Solar System. The Sun.

Chapter 17.4 ? 17.7

• Asteroids and Comets
• Our Own Star

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Remnants of the Solar Nebula
Small bodies remain virtually unchanged since
their formation 4.5 billion years ago They carry
history of the Solar system in their
compositions, locations, and numbers.
Asteroid means starlike, a rocky leftover Comet
means hair (Greek), an icy leftover Meteor a
thing in the air (falling star) Meteorite any
piece of rock than fell to the ground from the sky
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Asteroids
Undetectable to the naked eye (a.k.a. minor
planets) The first asteroid Ceres was discovered
by Piazzi in 1800 in an attempt to find the
missing planet between Mars and Jupiter Ceres
has a diameter of 500 km ( half of
Pluto) There are more than 100,000 asteroids
larger than 1 km in diameter The asteroid belt
lies between 2.2 and 3.3 A.U.
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Finding Asteroids
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Asteroid Vesta
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Asteroid Eros
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Missing planet
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Origin and evolution of the Belt
The most likely reason for the belt existence is
orbital resonances
A resonance occurs if an objects orbital period
is a simple ratio of anothers object period
(1/2, 1/4,etc.) Asteroids with resonance periods
will be pushed out of their orbits by large
planets (e.g., Jupiter)
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Asteroid belt
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Meteor
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Tunguska Meteorite
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Leonid Meteor Shower
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Meteorites
Meteorites are pieces of rock falling from the
sky. Seen as fireballs (sometimes with sound)
Primitive meteorites composed of a random mix of
flakes from the solar nebula, contain pure
metals, which are bound in minerals on Earth.
Processed meteorites parts of a larger
object. Some resemble the Earths core, others
are similar to the Earths crust and mantle.
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Primitive Meteorites
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Comets
Comets are basically dirty snowballs where ice
mixes with rocky dust. Their mean size is a few
kilometers across.
Comets change appearance when they approach the
Sun. The comet body is called nucleus. Sublimating
ices create coma. A tail pointing away from the
Sun appears. There are two tails plasma tail and
dust tail.
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Comet Orbits
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The Origin of Comets
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Comet Hale-Bopp
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Sun Grazing Comets
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Pluto
Pluto was discovered in 1930 by Claude Tombaugh.
Its radius is 1,195 km and mass is 0.0025 Earth
mass. Its orbital period is 248 years. It was
closer to the Sun than Neptune in 1979
1999. At aphelion it is 50 AU from the Sun. Its
moon Charon was discovered in 1978.
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Pluto and Charon
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Pluto and Charon
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Summary of Small Objects
Asteroids and comets are the best evidence of how
the solar system formed The small bodies are
significantly affected by planets
gravity. Impacts with comets and meteorites are
spectacular events, but may even alter
life. Pluto has more similarities with the
Kuiper belt comets.
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Why Does the Sun Shine?
Ancient view a hot, glowing rock of the size of
Massachusetts
Early XIX century cooling or chemical
reactions Enough energy for a few thousand years
Late XIX century gravitational
contraction Enough energy for 25 million years
XX century nuclear fusion Can shine for 10
billion years
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Current State of the Sun
The Suns size is stable, maintained by a balance
between the force of gravity and gas
pressure. This balance is called hydrostatic or
gravitational equilibrium.
Gravitational equilibrium implies that the
pressure increases with depth. This makes the Sun
extremely hot and depth in its core.
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Gravitational Equilibrium
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Big Picture of the Sun
The Sun contains 70 hydrogen, 28 helium, and 2
heavier elements.
The total power output (luminosity) is 3.8 1026
W. 1Watt 1 joule/second
The radius is 700,000 km. The mass is 2 1030
kilograms (300,000 times more massive than the
Earth).
The surface temperature is 5,800 K
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Nuclear Fusion
Nuclear fusion is the process of combining nuclei
to make a nucleus with a greater number of
protons and neutrons.
Particles in a nucleus are held together by the
strong force. This is the only force that can
overcome the electromagnetic repulsion between
two positively charged nuclei.
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Hydrogen Fusion in the Sun
The proton-proton chain
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Solar Neutrino
Neutrino is a subatomic particle. It is a
by-product of the solar proton-proton cycle. It
barely interacts with anything.
Counts of neutrino coming from the Sun are
crucial to test our knowledge about solar physics.
Neutrino observatories use huge amounts of
different substances to detect nuclear reactions
with neutrino. So far theory predicts more
neutrino than is seen.
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Observations of Solar Neutrino
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The Super Kamiokande Experiment
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How does the Light Comes Out?
Photons are created in the nuclear fusion
cycle. They collide with other charged particles
and change their direction (random walk). They
also decrease their energy while walking. It
takes 10 million year to get outside.
The random bouncing occurs in the radiation zone
(from the core to 70 of the Suns radius). At
Tlt2 million K, the convection zone carries
photons further towards the surface.
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Sunspots and Other Solar Activity
Sunspots have T4,000 K, cooler than the 5,800 K
surrounding plasma.
Sunspots are kept together by strong magnetic
fields. Usually sunspot appear in pairs connected
by a loop of magnetic field lines.
The loops rising into the chromosphere or corona
may appear as solar prominences.
Solar flares are events releasing a lot of energy
where magnetic field lines break.
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Sunspot Close-Up
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The Sunspot Cycle
Observations of the Sun since the beginning of
the telescopic era revealed that the number of
sunspots gradually rises and declines.
An average period is 11 years (from 7 to 15
years). The magnetic fields in sunspots reverse
their direction when a cycle is over.
No sunspots were observed in 1645?1715, when a
Little Ice Age took place in Europe and America.
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The Sunspot Cycle
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Summary of the Sun
The Sun shines with energy generated by fusion of
hydrogen into helium in its core. Gravitational
equilibrium determines the Suns interior
structure and maintains a steady nuclear burning
rate. The Sun is the only star near enough to
study it in great detail.