Download The Cosmic Cupboard

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?
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.
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.
Control room in
Trailer
•The receiver further
amplifies the signal
and passes it to the
control room where
astronomers are
looking at the data.
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
This is an
optical
image of
Jupiter
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.
This is an
optical
image of an
elliptical
galaxy
called NGC
6251
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
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.
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.
Spectrum of
NGC 3783
(black). The
most important
spectral features
in the data and
model are
labelled.
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.
Most abundant
elements, H2 and He
100 times less abundant
elements, C, N, O & Ne
100 times less abundant
again
Trace
abundances
Cosmic Abundance of
the Elements
hydrogen
helium
oxygen
carbon
neon
nitrogen
10,000,000
1,400,000
6,800
3,000
2,800
910
magnesium
290
silicon
250
95
sulfur
80
iron
42
argon
aluminum 19
17
sodium
17
calcium
all other
50
elements
.
.
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.
Examine this list of cosmic
abundances. What molecules
Cosmic
Abundance
of
(combinations of elements) are likely to form from
the
Elements
random
collisions
in a mixture of these gases?
hydrogen
helium
oxygen
carbon
neon
nitrogen
10,000,000
1,400,000
6,800
3,000
2,800
910
magnesium
290
silicon
250
sulfur
iron
argon
aluminum
sodium
calcium
all other
elements
.
95
80
42
19
17
17
50
.
Ignore Helium an Neon
because these are Inert gases
that
Cosmic
Abundance
of
will not form any molecules (except under some very
the
Elements
artificial
circumstances
in the laboratory.
hydrogen
helium
oxygen
carbon
neon
nitrogen
10,000,000
1,400,000
6,800
3,000
2,800
910
magnesium
290
silicon
250
sulfur
iron
argon
aluminum
sodium
calcium
all other
elements
.
95
80
42
19
17
17
50
.
IfCosmic
two atoms were to “bump”
into each other in this mixture,
Abundance
of
what two atoms would they be? Since Hydrogen represents the
overwhelmingthe
majority Elements
of atoms, the two would be H and they
would form a molecule H2, molecular hydrogen.
hydrogen
helium
oxygen
carbon
neon
nitrogen
10,000,000
1,400,000
6,800
3,000
2,800
910
magnesium
290
silicon
250
sulfur
iron
argon
aluminum
sodium
calcium
all other
elements
.
95
80
42
19
17
17
50
.
What molecule would form next? That is, after H-H collisions, what
would
be the next
most
common
collision?
itof
would be
What
molecule
would
form
next? That
is, afterClearly
H-H collisions,
Cosmic
Abundance
between
hydrogen
H2O. Water
is the Clearly
second it
most
what
wouold
be the and
nextoxygen,
most common
collision?
the
Elements
abundant
in
the
Universe.
Water H
is2O.
everywhere
would bemolecule
between
hydrogen
and oxygen,
Water is (in
the some
form). in the Universe.
second most abundant molecule
hydrogen
helium
oxygen
carbon
neon
nitrogen
10,000,000
1,400,000
6,800
3,000
2,800
910
magnesium
290
silicon
250
sulfur
iron
argon
aluminum
sodium
calcium
all other
elements
.
95
80
42
19
17
17
50
.
We could continue this “collisional” analysis, looking at
Cosmic
Abundance
what
molecules would
be the next most common, butof
I’d
rather just present
results and let you see that nature has
thethe Elements
made or job of understanding what goes into making a
planet a bit simpler that we may have though.
hydrogen
helium
oxygen
carbon
neon
nitrogen
10,000,000
1,400,000
6,800
3,000
2,800
910
magnesium
290
silicon
250
sulfur
iron
argon
aluminum
sodium
calcium
all other
elements
.
95
80
42
19
17
17
50
.
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.
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”
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.
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)
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…
10,000
Parts
GAS
100
Parts
ICE
1
Part
Rock
GAS
Let’s 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!
ICE
Rock
How will this material sort out around a
young star?
GAS
ICE
Rock
The Distribution of Materials in the Solar Nebula
10,000
Amount of Material
Gas is everywhere and
most abundant
Ice is next in abundance
100
Rock is least in
abundance
1
Distance from the Proto-Sun
The Distribution of Materials in the Solar Nebula
Amount of Material
10,000
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.
100
1
Distance from the Proto-Sun
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.
The Distribution of Materials in the Solar Nebula
Amount of Material
10,000
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.
100
1
Ice
Line
Distance from the Proto-Sun
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
Amount of Material
10,000
100
1
IceLine
Distance from the Proto-Sun
The Distribution of Materials in the Solar Nebula
Amount of Material
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
1
Ice
Line
Distance from the Proto-Sun