Why is the chemical composition of the Earth and the other terrestrial planets so different from the sun?
May 6, 2010 by sunli
Filed under Sun chemical
Why is the chemical composition of the Earth and the other terrestrial planets so different from that of the sun? Why is the chemical composition of Jupiter and other Jovian planets more similar to the sun’s?
The sun is made up of hydrogen and helium,the planet are made up mostly of rocky material and a bit of everything else.
Think of the outer gaseous planets (Jovian planets), such as Jupiter, as large failed stars. They formed, likely, in the outer regions of the solar system around the same time that the Sun formed. The Sun became the dominant mass that, with enough gravitational pressure, was able to kickstart and sustain nuclear fusion. The initial stages of fusion is what is thought to have produced the inner planets and the asteroid belt (rocky material, heavy metals, and other elements, etc). Perhaps this is why we see the rocky planets with an abundance of elemental variety close to the center of the Solar System and the gaseous planets on the outer regions.
Since the Sun lives off of fusing hydrogen, any other compounds/elements are either ejected into space or were already formed when the Solar system was coming together and in the early stages of the Sun’s birth/life.
Pluto does not count any more, as it along with the other known “dwarf planets” and all the comets are considered Kuipier Belt objects and consist of frozen materials such as methane, water, and ammonia (note that the common element in those three compounds is hydrogen). These KBO (Kuipier Belt Objects) formed much like the gaseous planets or were ejected from some larger source. They are frozen because their mass is not great enough to put heavy tension and pressure at the core such as Jupiter does, which in the case of the Jovian planets, produces a lot of heat and radiation (and friction) which keeps those compounds gaseous and flowing.
EDIT:
Jeff: The most abundant elements (iron and smaller weight elements) are what is formed in our Sun. Everything else, we’re not sure. Could have come from supernovae that occured near by. Our Sun and this Solar system quite possibly was born out of the remnants of ancient (on the scale of the universe) stars that were much larger and died violently. So I agree with you there. So those lesser available (heavier than Iron) elements, such as Gold and Platinum, and even Uranium/Plutonium are all likely offspring of some massive star collapse and a neutron star running rampant.
OK, I’m not the expert here, but I do differ with some of what tekwatcher said. Yes, the heavier elements were created by fusion within stars, but not within our sun! A fusion reaction cannot create elements higher than iron because energy is actually required to make larger atoms. Those elements all come from the energy of a supernova. Supernovae from the early universe seeded many of the higher elements that we see today. The elements below iron were created by the fusion reactions that powered the star, and the elements above iron were created by the energy of the supernovae themselves. All of those early stars were much larger than our sun and capable of higher fusion reactions. Our sun is mainly turning hydrogen into helium right now, so there’s no connection between our sun and the higher elements in the closer planets.
Here’s where my knowledge is a little sketchy and I encourage you to read further for more info. But there is a balance between the solar wind and gravity and friction in the early disk of the solar system. Basically, I think the solar wind tends to either blow the gasses away, or friction causes small particles to fall into the sun or inner planets. There is also an interaction with the so-called “frost line” which is the distance from the sun where water freezes and ice forms and is less blown by the solar wind. All of this has an effect of sorting out the gasses and the rocky debris, leaving the gassy planets further from the sun and the rocky planets closer to the sun. This process is still not exactly understood by astronomers, as I believe that they have recently discovered some gas giant planets that are too close too stars (other than our sun) according to what the theory would predict. So it’s a great question, and probably one that astronomers are still working on the details, although they know the major, driving mechanisms. There was a great article recently, I think perhaps in National Geographic, that explained this sorting of protoplanetary material. I’ve also given a link to the wikipedia article on planetary formation, which explains some of this (and I have not checked my meager explanation against this). Again, please read that and don’t go by what I say here.
The only thing I insist upon is that the actual elemental material was not produced by our sun, but rather by earlier supernovae.
The Sun is the power house that makes all of the other things.
Hydrogen (Sun) is turned by fusion into other elements, simple chemistry does the rest.
The gaseous giants could have been short life suns, but didn’t make it (lucky for us).
The gaseous planets are now made up of hydro carbons due to pressure and heat, the required flash over into suns just didn’t happen.
Simple as I can make it:
The sun and planets formed from a disk of dust and gas.
The sun formed first, and as it began to emit energy, it drove
much of the lighter elements outward. (Google or Wiki ‘Solar Wind’.)
The inner planets formed from a greater concentration of the denser
stuff that was harder to blow away.