The biggest myth about outer space is in the name: Space.
Everyone thinks it’s empty.
I mean, why wouldn’t they? It says right there. Outer. Space.
So, why wouldn’t anyone think it’s anything but a vacuum!
Well, it’s not!
It’s teeming with a lot of stuff and activity. Just not as much as on Earth or any heavenly body, but enough to matter (no pun intended).
Image Credits: Stock photo, pixabay.
So, What’s Filling Up the Space?
Well, some of the things are familiar to us – atoms, dust, plasma, radiation, and so on.
Of course, when you leave the Earth and enter outer space, the matter density drops to negligible levels. There’s no question about that.
But, even in that seemingly vacuous space, there’s quite a bit of stuff, although not in any meaningful quantities for us to bother about it.
Think of it like this: On Earth, you have a high density of matter. As you fly into outer space, the density keeps dropping until you exit the atmosphere, when it hits negligible levels. Then, as you approach another planet, the density increases from negligible levels to a meaningful degree.
But, The Density Changes Too
Stars like the Sun have a kind of bubble or sphere of influence that can extend for light-years.
Within this halo, you’ll find an abundance of solar storms, coronal mass ejections, and other activity adding to that density.
So, matter density within this heliosphere is usually higher than what it is in the space between stars, which is even more sparse.
Things get really interesting between galaxies.
This is where matter density is the least. Lower than what’s in both interstellar and stellar systems’ space.
In short, intergalactic space is the least dense, followed by interstellar space within galaxies, and finally the stellar system space.
In general, there’s about 1 atom per cubic centimeter of interstellar medium. The intergalactic medium has an even lower average density of 1 atom per cubic meter.
And, There are Exceptions
So far, we’ve discussed only the regular baryonic matter that makes up the things we know – planets, air, water, life, etc.
But that’s not everything.
There’s the more exotic stuff you won’t easily find on Earth: cosmic rays, dark matter, neutrinos, and dark energy. Dark matter is present within galaxies, and sometimes, outside too.
And every square inch of space is bombarded with hundreds of billions of neutrinos per second, especially in stellar systems.
And the ever-present quantum fluctuations don’t relent just because you are in outer space.
Vacuum energy, or zero-point energy, pervades the space, even in regions with the lowest energy density.
In a Nutshell
Think of outer space as an extremely low-density region with a lot of activity happening in it.
It’s not some inert, empty vacuum. It’s bubbling with activity, especially within galaxies.