https://www.reddit.com/r/askscience/comments/1j6r1n0/where_does_helium_go_once_it_escapes_our/
created by [deleted] on 08/03/2025 at 21:09 UTC
568 upvotes, 12 top-level comments (showing 12)
I can’t find a clear answer online, how fast is it moving in space? If the sun is shooting off helium, where is it all going, does it move forever or collect in gas clouds eventually?
Comment by somewhat_random at 08/03/2025 at 22:37 UTC*
363 upvotes, 10 direct replies
A helium molecule is like any other mass. It is held on earth by gravity and if it has enough velocity (without hitting something, usually another gas particle) it will escape earth's atmosphere. As the probability of hitting something drops, depending on its velocity it may orbit earth, escape earth and stay in the solar system (orbit the sun) or simply go out into deep space. The reason helium tends to escape is because it is lighter than any other gas (except free hydrogen which is rare). Since gas molecules are constantly colliding, the lighter ones are pulled down a little less by gravity so after many collisions will migrate to the upper atmosphere.
Comment by OlympusMons94 at 09/03/2025 at 09:24 UTC*
26 upvotes, 0 direct replies
Helium rises to the upper atmosphere, and much of it gets ionized to He+ by radiation. These ions get trapped and directed by Earth's magnetic field. The primary escape mechanism for helium from Earth is this He+ (along with H+ and O+) flowing out along open magnetic field lines near Earth's magnetic poles. This polar wind[1] escapes Earth, and mixes with the solar wind.
1: https://en.wikipedia.org/wiki/Polar_wind
Regardless of the specific escape mechanism, helium and other gas particles escaping the atmosphere ultimately mix and merge with the solar wind. The solar wind itself is composed in part of He+ ions (alpha aprticles), altbough it is mostly hydrogen ions (protons). The solar wind travels outwards from the Sun and spreads out through the heliosphere[2].
2: https://en.wikipedia.org/wiki/Heliosphere
The heliosphere ends at the heliopause, where the pressure of the outgoing solar wind is balanced by that of the interstellar medium[3]. There, the solar wind particles merge with the ISM. The heliosphere is teardrop shaped, with a spherical radius of ~120 AU (18 billion km), but a long (~350 AU / 52 billion km) tail extending in one direction. When it is said that the Voyager probes have left the solar system, this is referring to them having crossed the heliopause. (The gravitaitonal dominance of the Sun, i.e. including the scattered disk and Oort cloud, extends to several hundred to a thousand times the radius of the heliosphere.)
3: https://en.wikipedia.org/wiki/Interstellar_medium
Comment by KenethSargatanas at 08/03/2025 at 22:04 UTC
202 upvotes, 2 direct replies
The space between stars is full of very diffuse gas called "The Interstellar Medium."
It's mostly Hydrogen and Helium, but there are other bits of stuff floating around in it too. It will clump up into gas clouds under it's own gravity here and there. These denser parts of space are where a lot of star formation happens. They're called "Stellar Nurseries" A really famous one is called "The Pillars of Creation."
Comment by Probable_Bot1236 at 08/03/2025 at 22:49 UTC*
31 upvotes, 0 direct replies
does it move forever or collect in gas clouds eventually?
Space is sufficiently vast that it just basically spreads out, for all practical purposes, "forever". It's not aggregating into anything of higher density than the surrounding area, i.e. "gas clouds". It eventually becomes of low enough energy that diffusion is the dominant mechanism of movement, and this, coupled with the utter vastness and emptiness of space, means it's perpetually thinning even further out into and ultimately joining with the near-vacuum of deep space.
Most estimates of the interstellar medium (the "empty" space between stars within the galaxy) are at around 10^(-22) kg/m^(3). This is fully a hundred times less dense than the 'vacuum' surrounding the Earth at its orbital distance from the Sun. The estimated volume of the galaxy is about 15 trillion cubic *light years*.
The point of the above paragraph being this: space is a HUGE empty sink for gases to escape into. For the practical purposes of considering gas loss from an individual planet, i.e. Earth, it is truly, effectively infinite. **The answer to "where do the gases go" is simply "away". And the amount of "away" in the universe is basically unfathomable.** It's not running out of space for those gases to diffuse into (that is, spread out into) any time soon. Or actually ever:
If you were to spread all the mass of the galaxy out within its volume equally, it would still have an average density of a little less than half that of the Karman Line, the conventional altitude used to designate the start of space over Earth's atmosphere. And of course, most of the universe is empty space between galaxies. There's a lot of room for gases to escape into...
Comment by blashimov at 08/03/2025 at 22:03 UTC
27 upvotes, 1 direct replies
It just gets lost in space. Maybe in orbit around the sun still but shot off the earth. There's not enough gravity to really collect it unless it falls in a star, same way stars form from hydrogen gas in space too.
Comment by accidental_Ocelot at 09/03/2025 at 23:15 UTC
3 upvotes, 0 direct replies
it could go up till it escapes earth's influence it could be blow by solar wind until it reaches the heliopause where the solar wind meets the galactic winds and creates sort of a demarcation where the solar wind is equal to the galactic wind. the heliopause if I remember right is about 4 billion miles from the sun but it is not spherical its more of an egg shape.
here is a cool video that explains it and renders it in 3d.
https://youtu.be/fSbm5LCJspk?si=InNICekb_W3nTCw1
Comment by [deleted] at 08/03/2025 at 23:00 UTC
12 upvotes, 2 direct replies
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Comment by KRed75 at 08/03/2025 at 22:06 UTC
6 upvotes, 0 direct replies
It just spreads out in space. The helium from the sun is forced to the core mostly where it accumulates. Helium that manages to escape the sun will also just drift slowly in space. It may eventually accumulate and be captured by new stars.
Eventually, when the sun runs out of hydrogen, it'll become so dense that it'll start fusing helium atoms and will become a red giant. The result of helium fusion is mostly carbon and oxygen.
Comment by groveborn at 09/03/2025 at 00:14 UTC
2 upvotes, 0 direct replies
It's just at the top. If it's not being held well enough then the solar winds, which can include helium, blow it off. If no longer held to our planet it'll be in interplanetary space.
There is a bunch of such stuff out there.
Comment by [deleted] at 08/03/2025 at 22:05 UTC
1 upvotes, 0 direct replies
[removed]
Comment by eatabean at 09/03/2025 at 07:19 UTC
1 upvotes, 0 direct replies
Is it the solar wind stripping away the H and He molecules that have risen to the upper atmosphere? Would that produce irregular (observable) clouds of these gasses in the solar system? Would they flow outward or be pulled inward by the sun's gravitational effect? Or funneled in towards more massive bodies like Jupiter or Saturn! Are they polarized?
Comment by Distelzombie at 12/03/2025 at 13:58 UTC
1 upvotes, 0 direct replies
They escape because they move faster than escape velocity - because they are so low in mass, when they are in a sphere of influence of another, bigger atom, they get much faster than i.e. a nitrogen atom would.
So it depends on how fast they move: Some probably escape the solar system, some settle around the moon, most are probably confined to a gas cloud around our earth-moon system. After that, anything that attracts might catch them or divert their course onto another celestial body. And the fortunate rest, with exceptions, will become part of the solar-radiation-shockwave voyager detected at the edge of our solarsystem. Maybe even become part of some nebula in our arm of the galaxy. Won't they? (Citation needed)
Ergo the answer is "everywhere".