This is from the BBC. The secrets lurking beneath the Black Sea see:(00:18-00:20)
"So, just how deep is the Black Sea."
I know that this sentence still perfectly makes sense if the word "just" is not used at all. Here it is: "So, how deep ....." makes sense, doesn't it?
Also, I am sure there must be a reason why one would include "just" in this sentence. It certainly must have a function. I looked up "just" again, and checked 18 senses in the dictionary, none of which fits in this sentence. Collins dictionary, meaning of just
So, I want to ask, why do we need the word "just" here? What kind of contribution does it make on the meaning of the sentence? Does it make the sentence more curious or more unknown?