Any difference in meaning: "So, just how deep is the Black Sea." / "So, how deep is the Black Sea."

Question

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?

Answer 1

This is sense 16 of Collins. "Use just to indicate you are asking for exact information".

You could paraphrase as "So, exactly how deep is the Black Sea". As it is a rhetorical question, you can infer that an estimate has previously been made, but the TV show will next tell you about the measurement of depth (using sonar or something similar)

It emphasises the need for exactness, but it is an optional part of the sentence, and a weak modifier - so it could be omitted without much difference in meaning, and really is little more than verbal "filler", since the default meaning of "How much" is asking for the exact value.