There is a vast literature on this topic but this important question/problem is still _____ .
Among the questions/problems that are yet ______ in this field is about the relation between X and Y.
I am looking for a verb to say that there is no answer at all for that question, or that there is no noticeable answer or approaches to answer it, or that the question is still quite open.
I can simply say unanswered but that seems a bit too determined. I also thought of open and then I came to unsettled which seems to me the most idiomatic option in that context. What do you think? Any other suggestions?