The Cosmic Cupboard

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The Cosmic Cupboard

• How do astronomers know what elements are in the
  universe to make planets from?
• What is the cosmic abundance of elements?
• What molecules will result from this cosmic
  abundance?
• How will these materials sort themselves around a
  young star?

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Radio Telescopes can detect the spectral
signature of elements across the universe.

• Natural radio emission from elements can travel
  vast distances.
• Terrestrial radio telescopes are very sensitive.
• Searches for elements in the interstellar medium
  and in external galaxies have been made.

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Receiver

• This is a typical stand alone radio telescope
• Natural radio emission is collected by the dish
• The disk reflects the radio ways and concentrates
  them at the receiver.
• The receiver further amplifies the signal and
  passes it to the control room where astronomers
  are looking at the data.

Control room in Trailer
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This array of Radio Telescopes in New Mexico has
21 separate radio telescopes that can be operated
independently or electronically arrayed together
to act as one giant radio telescope of
unsurpassed resolution
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This is an optical image of Jupiter
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This is a radio image of Jupiter. The radio
images shows a band of emission around the
equatorial region similar to the Van Allen Belts
around the Earth.
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This is an optical image of an elliptical galaxy
called NGC 6251
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Radio Lobes
Radio Jets
This is a radio image of the same elliptical
galaxy NGC 625. The visual galaxy does not
appear. Instead, two large lobes of radio
emission appear from jets that are believe to
originate from a super massive black hole in the
center of the galaxy
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This is a combined optical and Radio image. The
point is to show you that the radio telescopes
can detect structures that are not visible in
ordinary optical telescopes.
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The Cosmic Abundance of Elements

• Hydrogen is the overwhelmingly most abundant
  element in the universe 87.6
• Helium is next in abundance 12.3
• These two elements comprise 99.9 of the atoms in
  the universe.
• All other elements are in very low abundance.

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This 13 mm spectrum of the molecular cloud
SgrB2(N) near the Galactic center is completely
dominated by molecular lines from known and
unknown (U) species (Ziurys et al. 2006, NRAO
Newsletter, 109, 11).  More than 140 different
molecules containing up to 13 atoms (HC11N) have
been identified in space.
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Spectrum of NGC 3783 (black). The most important
spectral features in the data and model are
labelled.
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Most abundant elements, H2 and He
100 times less abundant elements, C, N, O Ne
100 times less abundant again
Trace abundances
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Abundance of Molecules in the Universe

• In space, molecules are formed by collisions
  between atoms.
• The most common molecules will be formed from
  atoms that are most likely to collide with each
  other.
• The Nobel gases Helium and Neon will not form
  bonds with other elements.

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Examine this list of cosmic abundances. What
molecules (combinations of elements) are likely
to form from random collisions in a mixture of
these gases?
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Ignore Helium an Neon because these are Inert
gases that will not form any molecules (except
under some very artificial circumstances in the
laboratory.
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If two atoms were to bump into each other in
this mixture, what two atoms would they be?
Since Hydrogen represents the overwhelming
majority of atoms, the two would be H and they
would form a molecule H2, molecular hydrogen.
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What molecule would form next? That is, after
H-H collisions, what would be the next most
common collision? Clearly it would be between
hydrogen and oxygen, H2O. Water is the second
most abundant molecule in the Universe. Water is
everywhere (in some form).
What molecule would form next? That is, after
H-H collisions, what wouold be the next most
common collision? Clearly it would be between
hydrogen and oxygen, H2O. Water is the second
most abundant molecule in the Universe.
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We could continue this collisional analysis,
looking at what molecules would be the next most
common, but Id rather just present the results
and let you see that nature has made or job of
understanding what goes into making a planet a
bit simpler that we may have though.
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The most common molecules in space that planets
are constructed from begins with

• Molecular Hydrogen and Helium
• Helium is not really a molecule but we will count
  it now because of its high abundance.
• These two GASES represent the overwhelming amount
  of material that stars and planets form from.

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Next, we find a class of molecules we will call
ICES

• Water, H2O
• Methane, CH4
• Ammonia, NH3
• Carbon Dioxide, CO2
• These molecules are solid when cold, but will
  vaporize when warmed. Thus the moniker Ices

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Finally, we come to the last class of molecules
that we will collectively call Rock

• Quartz, SiO4
• Silicate Minerals (SiO3 (Fe, Mg, AL, etc..)
• are the common minerals that make up the igneous
  rocks of the Earth.
• Metallic Iron, Fe
• Metallic Nickle, Ni
• These molecules are solid when cold, and remain
  solid unless heated to exceptionally high
  temperatures. Thus, we will consider them to be
  always solid.

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The Cosmic Cupboard

• We have clearly oversimplified the chemistry
  occurring in the cosmos. However, we have not
  deviated from its true outcome.
• There are three basic ingredients available to
  built planets
• Gas (H2, He)
• Ices (H2O, CH4, NH3, CO2)
• And Rock (Silicate Minerals, Iron and Nickle)

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The Cosmic Cupboard

• Gas (H2, He) is the overwhelmingly abundant
  material.
• Ices (H2O, CH4, NH3, CO2) are perhaps 100 times
  less abundant than gases, and
• Rock (Silicate Minerals, Iron and Nickel) is 100
  times less abundant than Ices.
• Imagine the following cupboard of ingredients
  from which you can make a planet

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10,000 Parts
GAS
100 Parts
1 Part
ICE
Rock
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Lets make a simple deduction. Why are there no
giant planets in our Solar System made entirely
of Rock. In other words why do we not see any
Jupiter sized Terrestrial Planets? Obviously,
there is not enough rock available. You cannot
make a giant planet out of a tiny container of
rock. Thus we can understand why the Terrestrial
planets are so small. They are made of the least
abundant material!
GAS
ICE
Rock
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How will this material sort out around a young
star?
GAS
ICE
Rock
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The Distribution of Materials in the Solar Nebula
10,000
Gas is everywhere and most abundant
Ice is next in abundance
100
Amount of Material
Rock is least in abundance
1
Distance from the Proto-Sun
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The Distribution of Materials in the Solar Nebula
Ices too close to the Proto-Sun evaporate and
become gases. Thus, solid ices begin only beyond
a distance from the Proto-Sun we will call the
Ice Line.
10,000
100
Amount of Material
1
Distance from the Proto-Sun
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Underlying Planet Formation Facts

• All planets begin forming by an accumulation of
  solid material.
• Close to the Sun only rock is available as a
  solid to form planetesimals.
• Far from the Sun ices constitute the vast bulk of
  solid material and icy planetesimals are common.
• There is hundreds of times more solid ice than
  rock. The reservoir of solid material to
  initiate planet formation is much larger when
  ices are solid.

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The Distribution of Materials in the Solar Nebula
Planets inside the Ice Line can only be small and
rocky. There is not enough rock and the gas is
too hot for them to accrete the Hydrogen and
Helium around them. Thus the planets in close
are small and rocky.
10,000
100
Amount of Material
1
Ice Line
Distance from the Proto-Sun
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Planets beyond the Ice Line have a much larger
reservoir of solid material to use. They have
Ice as well as Rock. There is a 100 times the
amount of Ice compared to Rock. So the planets
that form beyond the Ice Line start with much
larger planetary cores of Ice and Rock. These
large cores have enough gravity to accrete to
cold hydrogen and helium around them. Thus they
grow to be gas giant planets, even though they
started as mostly Ice and some rock cores.
The Distribution of Materials in the Solar Nebula
10,000
100
Amount of Material
1
IceLine
Distance from the Proto-Sun
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The Distribution of Materials in the Solar Nebula
10,000
Further, we can now see why Jupiter is the
largest Jovian planet because it had the largest
reservoir of solid material to form from and was
able to gather the most gas. The succeeding
Jovian planets all get smaller as the reservoir
of material diminishes.
100
Amount of Material
1
Ice Line
Distance from the Proto-Sun