Todays agenda 3a. Properties of planets

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Todays agenda3a. Properties of planets

• Planetary properties and formation processes
• Chemical properties of the solar system
• 3b. Meteorites
• Properties and characterization of meteorites

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The orbits of the planets are ellipses with the
Sun at one focus, though all except Mercury and
Pluto are very nearly circular.
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Almost all are orbiting in close to the same
plane, which is not far off (7 degrees) the
Suns equatorial plane.
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All planets orbit in the same sense, and
only Venus, Uranus, and Pluto have a retrograde
rotation
Obliquity is the angle between a planet's
equatorial plane and its orbital plane
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• Solar System Properties
• Patterns of Motion
• The planets all revolve around sun in same
  direction CCW. This is the same sense as the
  rotation of the Sun about its axis.
• All the planets lie roughly within sun's
  equatorial plane and the orbits of all the
  planets lie within 18º of the plane of the
  ecliptic ( plane of Earths orbit).
• With a couple of exceptions the planets have a
  prograde rotation (rotation in the same direction
  as they revolve about the Sun)
• Many, but not all, planets have moons and most
  moons orbit in the same sense as planetary
  orbits.
• 99.8 of the mass in solar system is in the Sun
• 99 of total angular momentum in the solar
  system is in planets

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Interstellar medium two phases diffuse
molecular cloud core Temper. 50 K 150
K Density 500 mol/cm3 108 mol/cm3
Each finger tip larger than our Solar
System Star light (UV) is evaporating these
placental clouds
60,000 AU
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The molecular cloud begins to collapse due to
gravitational instability
Nebula
As the cloud becomes smaller and denser 1)
rotation increases 2) flattens to disk 3) heats
up in the interior Obeys laws of angular
momentum
At disk center, temp. rises until 1 m degrees
enough to trigger nuclear fusion. For big stars
collapse continues until temp. reaches 10 m
degrees
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Nebular theory of Solar System Formation

• Gravitational collapse of the molecular cloud of
  gas and dust
• Rapid rotation to conserve angular momentum
  (size, shape, rotation) and
• flattening to a disk
• 3. Heating up of the core and formation of a
  protoplanetary disk

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Molecular Cloud Cold and dense
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Cloud fragment, 104 Au in size
Next frame
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Rotating object forms
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Rotating object begins to take shape
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100 Au across, protostar 1 Au
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Orion nebula
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Orion nebula
active star formation, hundreds to thousands of
stars will be born here
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Amino acids, the building blocks of life Where
do they come from? ISM? Made in the disk?
Definition A molecule of the general formula
NH2-CHR-COOH, where "R" is one of a number of
different side chains. Amino acids are the
building blocks of proteins.
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Accretion
Mechanisms must exist to go from fine dust less
than 1 micrometer in diameter to larger materials
that can begin to attract one another fractal
fluffy objects like this are thought to be key
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Planetisimal
Eventually leading to this, a planetesimal, in
this case preserved in the form of comet Wild-2
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• These planetesimals collided and grew into larger
  proto-rocky planets
• Collisions destroy the smaller ones but the
  larger ones re-accrete
• Runaway growth from large number of small objects
  to small number of larger objects

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Accretion of the terrestrial planets
Final accretion --- dissipation of the nebula
Grains - planetesimals
Planetary embryos --- era of violent collisions
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Why are planets spherical?

• Because of isostatic adjustment
• Gravitational field acts as though it originates
  from the center of the body and pulls everything
  toward the center
• Large size and internal heating from
  radioactivity makes it behave like a fluid. The
  only way to get all masses to clump together is
  to form a sphere

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Planetary differentiation

• Heating due to radioactivity, impact, and
  gravitational pressure melted parts of
  protoplanets as they grew toward being planets.
  In melted zones their heavier elements sank to
  the center while lighter elements rose to the
  surface.

• Composition of some meteorites show that
  differentiation took place in some asteroids.

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Extrasolar planet
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Planetary composition

• Rock- most common rocks are silicates i.e. oxides
  of silicon, magnesium and aluminum
• Metal- found in cores of planets mostly as iron
  and nickel
• Gas- predominantly as hydrogen and helium. Owes
  origin to nebula - gas and dust
• Ice- also referred to as volatiles. Most common
  is water, carbon dioxide, methane and ammonia

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Chemistry of planets

• Hydrogen and oxygen are the most abundant and
  chemically reactive elements in the universe
• Planetary matter-mostly gas, ice, rock and metal
• Vaporization close to the sun results in rocky
  planetary bodies composed of silicates (oxidizing
  conditions)
• At higher temperatures (mostly at the cores)
  rocks undergo chemical and structural
  transformation to form metals e.g. mercury is ¾
  metal
• Away from the sun, planets are made up of gas,
  ice and some silicates (reducing conditions)
• Rocks and metal are denser than gas and ice

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Interior of solar nebula heats up, external
regions stay cold
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Sun
Jupiter
Saturn
Uranus
Neptune
Mercury
Venus
Earth
Mars
Pluto
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Planetary composition
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• SUMMARY
• Properties of Planets
• The inner planets are small, dense, rocky bodies
  
• (terrestrial planets)
• a. Volatile elements (e.g., water) have reached
  the inner planets even though bulk compositions
  of the planets suggest formation at high
  temperatures
• The outer planets are gaseous giants (Jovian
  planets)
• Atmospheres rich in H and He
• All giant planets have systems of regular
  satellites, resembling miniature solar systems,
  and rings
• All 4 giant planets have 1 or more irregular
  satellites

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• Solar System Properties requiring explanation
• Properties of small bodies
• Asteroids are rocky bodies that occupy a wide
  belt between the orbits of Mars and Jupiter.
• Meteorites come from asteroids. Most are
  primitive, undifferentiated (chemically
  unequilibrated) rocks.
• Some meteorites are igneous (differentiated)
  rocks.
• Almost all meteorites are very old, having
  formation ages close to 4.6 billion years.
  Planetary ages are consistent with this upper
  limit.
• Comets are small icy bodies that come from the
  far reaches of the solar system.
• Kuiper belt and Oort cloud

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• Solar System Properties requiring explanation
• Exceptions and miscellanea
• There are exceptions to the rules
• Retrograde motions, inclined axes.
• Spacing of planets is almost regular
• Exception is the asteroid belt
• Mars is undersized
• Number and size of moons varies extensively
• Earth-Moon system almost a double planet
• Isotopic irregularities in some elements are
  widespread