Suppose a sound wave is emitted by an object in a medium like a gas so it travels in some direction. If the wave meets a rigid object, for example a wall, it reflects back as one should expect; and if it encounters another medium, like a denser one, it will be transmitted to the other side. In those cases the sound wave keeps traveling, and of course it can loose energy in its path and even be absorbed by some object, so it can be converted into another form of energy.
Now, I'm aware that sound waves can't travel in vacuum, so my question is: What happens to a sound wave that is traveling in some medium and encounters vacuum ?. Here's a drawing of the situation:
I'm thinking about the usual wave phenomenoma and reflection is not a logical option since there is not a defined object that can work like a wall, and transmission doesn't make any sense at all since sound waves can't travel through vacuum. So what happens with that wave ? Where does its energy go ?.