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.

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. Receiver Control room in Trailer

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

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 Radio Lobes Radio Jets

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, H 2 and He 100 times less abundant elements, C, N, O & Ne 100 times less abundant again Trace abundances

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 (combinations of elements) are likely to form from random collisions in a mixture of these gases?

Ignore Helium an Neon because these are Inert gases that will not form any molecules (except under some very artificial circumstances in the laboratory.

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 H 2, molecular hydrogen.

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, H 2 O. Water is the second most abundant molecule in the Universe. 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, H 2 O. Water is the second most abundant molecule in the Universe. Water is everywhere (in some form).

We could continue this “collisional” analysis, looking at what molecules would be the next most common, but I’d 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.

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, H 2 O Methane, CH 4 Ammonia, NH 3 Carbon Dioxide, CO 2 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, SiO 4 Silicate Minerals (SiO 3 + (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 (H 2, He) –Ices (H 2 O, CH 4, NH 3, CO 2 ) –And Rock (Silicate Minerals, Iron and Nickle)

The Cosmic Cupboard Gas (H 2, He) is the overwhelmingly abundant material. Ices (H 2 O, CH 4, NH 3, CO 2 ) 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…

GAS ICE Rock 1 Part 100 Parts 10,000 Parts

GAS ICE Rock 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!

GAS ICE Rock How will this material sort out around a young star?

The Distribution of Materials in the Solar Nebula Distance from the Proto-Sun Amount of Material Gas is everywhere and most abundant 10, Ice is next in abundance Rock is least in abundance

The Distribution of Materials in the Solar Nebula Distance from the Proto-Sun Amount of Material 10, 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.

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 Distance from the Proto-Sun Amount of Material 10, 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. Ice Line

The Distribution of Materials in the Solar Nebula Distance from the Proto-Sun Amount of Material 10, 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. IceLine

The Distribution of Materials in the Solar Nebula Distance from the Proto-Sun Amount of Material 10, 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. Ice Line