There is a lot of information on different star types and compositions.

Can we make estimates of the total mass of rock, ice, and non stellar matter that orbits stars based on star evolution models?

Take, for example, the sun - are there studies of the total mass of non-solar material associated with the sun and it's composition regardless of accretion. What about nearby stars?

Can we estimate how much non-incandescent material the galaxy contains aside from dark matter?


1 Answer 1


The composition of the gas from which stars and their planetary systems form is reasonably well known. About 1-2% of this gas is in the form of chemical elements heavier than Helium (the so-called metallicity of the gas).

A fraction of these "metals" - the iron, silicon, oxygen etc. is capable of forming dust and then accumulating to form "rocky" material.

So to answer your last question first, given the available reservoir it seems most unlikely that even 1% of the baryonic (normal) matter in the universe could be rocks, even if none of it were gathered into luminous stars and galaxies.

Forming stars are surrounded by circumstellar material from which planets and other rocks form. Observations of young stars suggest these discs can be as massive as 10% of the stellar mass, but more usually 1% or less. This means that as a fraction of the whole formed star system the rocks will be at most 1% of 10% (ie 0.1%) of the stellar mass. For a Sun-like star that means there's less than 330 Earth masses of rocky material around it.

  • $\begingroup$ Hi, thanks for the info's, i am finding some differences in the numbers, The sun is 330k earth masses so our solar system could contain 3-33k earth masses of non stellar material. However, jupiter is 320, saturn is 70, uranus is 14 and neptune is 14, the oort cloud is 5-50 earth masses, so we are missing 2500 earth masses in our solar system, it's closer to 0.1% here $\endgroup$ Sep 30, 2015 at 2:56
  • $\begingroup$ It's still a very concise answer, the circumstellar material is dust and gas, mostly hydrogen, and may be a few percent apparently. I am curious about mathematical models that can estimate precisely the mass of different elements in the galaxy and precise measurements of circumstellar material, the solar system seems to have 0.1 at present, perhaps the other .9% -9.9% fell into the sun, which would make sense. $\endgroup$ Sep 30, 2015 at 3:10
  • $\begingroup$ @ufomorace Your edit was incorrect. There could be as much as 330 Earth masses of potentially rocky material (ie elements heavier than He) around a protostar. $\endgroup$
    – ProfRob
    Sep 30, 2015 at 6:16
  • $\begingroup$ @ufomorace Gas giants are mostly H, He, not rocky material. Any left over material not incorporated into planets etc is either accreted by the star or blown away. $\endgroup$
    – ProfRob
    Sep 30, 2015 at 6:21

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