Is the diameter of our solar system known?

Answer

There’s no such thing as a galactic registry that records where a solar system ends and a new one begins, and how much no-man’s-land there is between them. So the definition of a ‘border’ for the solar system depends on how you look at it.

Obviously – and you may be referring to them – there are still objects that belong to our solar system rather than anything else and are far beyond where Voyagers are now. The so-called Oort cloud, a reservoir of comets catapulted far away during the early phases of the solar system, is up to 10,000 astronomical units away, and Voyagers are a long way from that.

What was actually meant here is that Voyagers have already reached the point where the solar wind (a stream of particles emitted from the Sun) can no longer compete with the galactic wind, the stream of particles that cycle through the galaxy. It is thus the place where the electromagnetic influence of the sun ceases to be significant, and from that point of view one enters interstellar space.

Personally, like you, I am inclined to identify the boundary of the solar system with the Oort cloud rather than with the so-called heliopause.