All,
I have a basic understanding that a lot of elements were brought to planets by comets, supernova explosions and so on.
Why didn’t the sun attract most of these comets and fragments from celestial explosions instead of the planets? And why was / is the sun mainly just hydrogen?
In: 105
The sun actually has similar composition to other planets in the solar system. Jupiter and Saturn are basically suns that are not heavy enough to undergo fusion. Other planets do not have this hydrogen because it was blown away by solar winds long time ago.The sun is mainly hydrogen because the universe is mainly hydrogen.
Lighter gasses get pulled in easier. It takes more force to move rocky solids. So in what started out as a cloud of dust pretty thoroughly mixed, the lighter gasses began to clump. As that got bigger, gravity got stronger. From the inside-out, you have lighter gases followed by metals and silicates, because that is how each of those respond to gravity.
The metals and silicates clumped together in much the same way as the lighter gases. And planets formed. A stable orbit was then achieved.
Outside of that, you have gases and ices that are too far away to get pulled into the sun. They clumped together and formed the gas giants and ice giants. Out there, it was a little less hydrogen, as that was more easily pulled to the center, which is one of the reasons Jupiter missed its big break to be a star.
Because the Universe is mostly made
up of Hydrogen, some Helium and a bit of Lithium. Three elements, that’s it. That is the total of what was created immediately following the big bang.
Everything else was created by the various different stars in their different stages of life.
Everything in the universe begins as hydrogen. Think of the sun as the universes material factory. Through nuclear fusion the sun will slowly over billions of years convert hydrogen and helium to every other element on the periodic table from number 3 all the way to our sun’s case iron. Smaller sun’s like ours hit iron and then they die because it takes more energy to go past iron then the conversion gives off. This will be when our sun goes through its last death throws and expands and takes out most of the solar system with it. Sun’s much larger than ours go through this cycle but they have such large gravitational energy they can keep going and will chug out the higher elements and then they to reach a critical point and die out and explode. Every single thing that exists in the universe was created in a star. The metal in your car from the carbon that makes up your body. All tangible matter other than hydrogen and helium was created and puked out all throughout the universe by stars. The biggest stars are the special ones. They reach a higher level of existence and then their deaths are the most spectacular events that exists. Not quite the largest stars will die in a spectacular fashion but leave their super heavy elements in their core as a super dense ball called a neutron star as they go supernova. These explosions are so large and powerful that one happened many many light years away and we could see it from earth. Even weirder are the ghosts these stars leave behind. They are crazy hot and spin rapidly and some which are called pulsars eject matter out like a laser beam. Then at the top of the universes scale are the largest giant stars that when they die they implode and they turn into black holes. And that is a whole other subject that defys everything you know about the world. So basically everything just gets recycled and will overtime find some other matter floating around and start clumping together to form planets or even get sucked in to another star or a black hole.
Edit: There is new theories that there are actually some elements that are not made by the supernova process but by in fact two of the neutron stars colliding.
Is there any reason to not believe that the same elements that make up the terrestrial planets, oxygen, silicon, iron, nickel, etc. aren’t also in the sun’s core, arriving there as dust and gas material accumulated and before the Sun protostar achieved fusion? Just buried underneath all of the hydrogen and helium, maybe in a plasma state?
One reason terrestrial planets have less hydrogen and helium is these gasses float away into space. Planets’ and moons’ gravity isn’t strong enough to hold them.
[This chart shows which gasses various planets and moons can hold.](https://physics.stackexchange.com/questions/615311/what-is-this-atmospheric-escape-chart-actually-showing). Gasses below planets or moons can be held by gravity. Gasses above planets and moons float off into space.
I am excited about recent findings about the star Betlegeuse which is about 640 light years ago. It is now believed that it is in the later stages of burning carbon before going supernova. Since it is a huge red giant and is only 10 million years old and could very well explode within a few decades. It would be bright enough to form a shadow and even be visible in daylight.
All of the material in the planets began life with the same composition as the Sun, but they’ve all evolved away from it. We know this from examining of a type of meteorite known as a carbonaceous chondrite, believed to have formed very early in the history of the Solar System. With the exception of gases – these strange black rocks have an elemental composition almost exactly the same as the Sun.
The planets smaller than Jupiter and Saturn don’t have strong enough gravity to hold on to the lightest elements like hydrogen and helium which make up most of the Sun. Closer in to the Sun, the heat and solar wind strip the elements with the lowest vaporisation points and blow them into space, so the inner planets are rocky with high concentrations of metals.
Later, as planets continue to evolve, factors like their internal heat become important. Neither Venus or Mars seem to have a churning metal core that generates a magnetic field, so in both cases, the solar wind has been busy stripping their atmospheres of light elements and blowing them into space.
The sun contains a LOT of matter other than hydrogen. Much more than all the inner planets combined. It’s just that the sun is, well, massive so the proportion of hydrogen to other elements is very high.
The inner planets do not have enough mass to hold on to their hydrogen, so what’s left is mostly heavy elements.
The outer planets (especially Jupiter) do have enough mass to hold on to hydrogen, so they are more similar to the composition of the Sun. Jupiter can be viewed as a failed star. Many star systems are binary, and Jupiter would have been the “other” star in our system if it were (considerably) larger.
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