Basically, since there's so little atmospheric material, any particles that you do set in motion will travel very far in a straight line before they hit another, which is a lot faster than hitting a bunch of particles erratically.

The catch is that you can only transmit very low frequency sounds - ti can be thought of like the variations in travel time for any individual particle drown out any high frequency signal.

In an ideal gas, speed of sound depends on the temperature and molar mass, but not density as the density terms cancel out: https://en.wikipedia.org/wiki/Ideal_gas#Speed_of_sound

It's hot, so the speed of sound is high.

Can you use it to transmit actual sound? Would it be possible to use this for short-range communication in space? Or is this only a very theoretical kind of sound?

Given the supersonic flow, one directional communication only.

Given the impedance mismatch[0], even the parts of the solar system outside Kármán lines where the interplanetary medium can support pressure levels equivalent to normal speaking (including low Earth orbit), I'm told human ears can't respond to that pressure change properly.

Sensors can be built to pick it up, but that may not be in scope for your question as we can also do that for acoustic waves in the CMB.

[0] https://en.wikipedia.org/wiki/Impedance_matching#Acoustics

I wouldn't expect human ears to be able to pick it up, because human ears would have far more serious problems just being exposed to the vacuum of space. But if it's possible to make sensors that can detect this sound, and devices that can generate it, and communication between the two would be accurate and really this fast, well, that would certainly be interesting.

Not sure if it would actually be useful, because I'm sure radio waves would be much more practical, but sound in space is a fascinating idea.