Astronomy Pic of the Day

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Astronomy Pic of the Day
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The Solar System
Ingredients?
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The Solar System
Ingredients?

• 1 Star the Sun
• 8 Planets a few minor planets
• 126 moons around these planets
• Asteroids, meteoroids, comets
• A lot of nearly empty space

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Questions

• What percentage of the total mass of the solar
  system does the Sun contribute?
• How is the solar system laid out in space?
  Spacing between planets? Orbital directions?

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Sun, Planets and Moon to scale
Sun accounts for 99.9 of solar system mass!
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An Easy Mnemonic
Mother Very Easily Made a Jam Sandwich Using Nect
arines
Mercury Venus Earth Mars asteroid
belt Jupiter Saturn Uranus Neptune
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Solar System Perspective
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Two Kinds of Planets
"Terrestrial" Mercury, Venus, Earth, Mars
"Jovian" Jupiter, Saturn, Uranus, Neptune
Distance from Sun? Size? Composition? Density? Rot
ation Rate? Number of moons? Rings? Heavy or
light Elements?
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Two Kinds of Planets
"Terrestrial" Mercury, Venus, Earth, Mars
"Jovian" Jupiter, Saturn, Uranus, Neptune
Far from the Sun Large Mostly Gaseous Low Density
Fast Rotation (0.41 - 0.72 days)? Many
Moons Rings Main Elements H, He
Close to the Sun Small Mostly Rocky High Density
Slow Rotation (1 - 243 days)? Few Moons No
Rings Heavier Elements
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Origin of Pluto
Large member of a class of objects in the outer
reaches of the Solar System
The Kuiper (pronounced K-eye-per) Belt Objects
100's found since 1992. Orbits tend to be more
tilted, like Pluto's. Leftover planetesimals
from Solar System formation?
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Questions

• What are some of the smaller objects (or debris)
  found in the solar system?
• What information do they contain that the planets
  and moons do not?
• (Hint What effects do erosion, geological
  activity, vulcanism, etc. have on a planet?)?

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Questions

• What are some of the smaller objects (or debris)
  found in the solar system?
• Comets, asteroids, meteoroids
• What information do they contain that the planets
  and moons do not?
• Solar system debris is unevolved gt gives direct
  evidence of conditions during solar system
  formation!

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Solar System Debris
Comets
Comet Halley (1986)?
Comet Hale-Bopp (1997)?
Short Period Comets
Long Period Comets
Few times 105 or 106 year orbits Orbits have
random orientations and large ellipticities Origi
nate in Oort Cloud
50-200 year orbits Orbits prograde, close to
plane of Solar System Originate in Kuiper Belt
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Oort Cloud is a huge, roughly spherical reservoir
of comets surrounding the Solar System. 108
objects?
A passing star may redirect Oort cloud objects,
creating long period comets. Kuiper Belt object
can be redirected by Neptune, creating a
short-period comet.
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Comet Structure
Coma and tail due to gas, dust, and ice warming
up and being removed from nucleus by the Solar
Wind. Far from Sun, comet is a nucleus
only. Highly Elliptical Orbits, exhibiting all
inclinations. Periods from hunderds to millions
of years.
Nucleus 1 - 10 km ball of ice, dust Coma
cloud of gas and dust around nucleus (106 km
across)? Tail Always points away from Sun.
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Comet Trajectory
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Meteor Showers
Comets break up when near Sun - solar wind,
evaporation, tidal force. e.g. Halley
loses 10 tons/sec when near Sun. Will
be destroyed in 40,000 years. Debris
spreads out along comet orbit. Intersection of
orbits gt meteor shower
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Asteroids
Most in Asteroid Belt, between Mars and Jupiter.
Predominently rocky. Typically smaller than
comets and larger than meteoroids. Largest are
spherical (gravity dominates) but smaller can be
irregularly shaped. If a potato represents an
asteroid in the asteroid belt how far away on
average (using the same scale) is the next
nearest potato?
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How did the Solar System Form?
What must be explained?

• Solar system is very flat.
• Planetary orbits are nearly circular.
• Almost all moons and planets (and Sun) rotate
  and revolve (orbit) in the same direction.
• Planets are isolated in space.
• Terrestrial - Jovian planet distinction.
• Leftover junk (comets and asteroids).

(Website Animation)?
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Nebular Theory

• Nebula Cloud of interstellar dust and gas about
  a light-year across
• Condensing (due to external perturbation) cloud
  heats up - star forms at center
• But why is solar system rotating and flat?

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Nebular Theory

• Nebula Cloud of interstellar dust and gas
  about a light-year across
• Condensing cloud heats up - star forms at center
• But why is solar system flat?
• Conservation of Angular Momentum Centrifugal
  Force
• Ang. Mom. mass x rotation speed x radius2
• Nebula collapses most rapidly along its axis of
  rotation flattens into a disk!

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Conservation of angular momentum?
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So, as nebula contracted it rotated faster. It
became a flattened disk, like a pizza crust.
(Centrifugal hoops demo)?
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But, clumps in rotating gas tend to disperse!
Need modified theory.
Solar Nebula 98
of mass is gas 2
in dust grains Condensation theory 1) Dust
grains act as "condensation nuclei - microscopic
platforms to which other atoms can attach,
forming larger and larger balls of matter. Also
radiate heat gt help to cool gas gt faster
gravitational collapse. 2) Accretion Clumps
collide and stick 3) Gravity-enhanced
accretion objects now have significant gravity
gt faster growth
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Asteroid Belt
Perhaps a planet was going to form there. But
Jupiter's strong gravity disrupted the
planetesimals' orbits, ejecting them out of Solar
System. The Belt is the few left behind.
And Finally . . .
Remaining gas swept out by intense period of
solar wind activity.
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Planetary Ejection