# Thread: Concentration of atoms in space

1. Does anyone know the concentration of atoms in interplanetary space is? (Per liter)

2.

3. Would it be constant? I'd think it would vary with what happens to the accumulated solar wind plasma and magnetic field. It probably isn't constant in the heliosphere but subject to distance from sun, solar activity, and other gravitaional forces from the outer planets and the galaxy itself.

It would definitley be less dense than an artificial vacuum created on Earth but I don't know how it could be measured the further one gets out from the Sun....especially past the inner planets.

(The value of my posting...zero. I completely defer to others on the subject)

4. I realise that it might vary, but I'm interested in the average atom concentration within the solarsystem. It is a question from a professor of mine. The alternatives are 0, 5000, 1.08*10^22 and 2.7*10^22.

Personally, I'm leaning towards 5000.. but I really don't know

5. I believe it's 0. Much of space is a near-vacuum. I once saw a figure of (I think) approximately 3 hydrogen atoms per cubic meter, or something like that in some regions of the universe.

6. I've been looking around the internet and in some books, and it seems that out of the four alternatives, 5000 is the closest.

Chemboy: You are right, the density in intergalactic and interstellar space is much smaller, but in interplanetary space it is somewhere between 5-10atoms/cm3.

Thanks for the input though

7. Originally Posted by Chemboy
I believe it's 0. Much of space is a near-vacuum. I once saw a figure of (I think) approximately 3 hydrogen atoms per cubic meter, or something like that in some regions of the universe.
I have no idea of the actual number but wouldn't be higher interplanetary than interstellar and, inter gallactic?

Rasti: profs aren't infallable... are you sure he means 'average'? In order to know that, one would have to know the frequency of other phenomena such as dust, grains, meteors, comets and so on. No one knows such information. If you have a trillion liters that have a value of 3 atoms and ony one liter has a value of 10 to the 12th power of atoms, then what's 'the average'....not 3.

I don't see how there can be any interstellar average unless other criteria are factored in. Does interplanetary mean between planets? Then what does the asteroid belt between Mars and Jupiter do to any number? Or comet with 10 to the nth power of atoms? Don't laugh, but even a human interplanetary spacecraft on route is how many atoms? It all depends which particular liter of interplanetary space is measured and they are not static as the atoms will change with other activity passing through.

8. I think he means that if you took all matter in our solar sytem and distributed them evenly.

9. Originally Posted by KALSTER
I think he means that if you took all matter in our solar sytem and distributed them evenly.
Including the sun?

I actually thinks he means the space between the planets. This isn't picking on Rasti. In science 101 it should be drummmed into a student (as it was into my skull) that the devil is indeed in the details of the question. Thus the need to be as clear as possible in defining terms. i used to think my profs were 'anal' in never letting fuzzy questions or answers getting though because all 'assumed ' what was meant and we were on the same wave length. Once I got into nitty gritty research, I saw the importance of why the profs were so diligent in holding our feet to the fire of clarity.

10. I support Jellyologist's comments on the importance of precision in questions (and answers) 100%. I also agree totally with this statement.
Originally Posted by Jellyologist
[I actually thinks he means the space between the planets.
Where I differ is that you do not need to think this is what is meant, it is clearly stated that this is what is meant.
The clue is in the word interplanetary - between planets.

We might have an interest, as J-Lo points out, in three vacuum densities:

1. Interplanetary
2. Interstellar
3. Intergalactic

The entire Universe (including all the stars, planets, black holes, dust, etc) has an average density of 1 atom per cubic metre.
The interstellar medium seems to average around 1 atom per cubic centimetre.
Values for interplanetary space are, strangely, harder to pin down. I would expect a difference between the plane of the ecliptic and above (or below) the plane.

11. I think I was a bit unclear

What I meant with interplanetary space was the part of space in between the planets in a solar system where there are no planets, asteroids, comets, stars etc.

The number 5-10 atoms/cm3 is based on calculations and measurements in our own solar system. The reason that this number is much higher than in, let's say, intergalactic space is that there is solar wind and similar phenomenons (spelling?) in interplanetary space

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