How are we sure Challenger Deep is the deepest point when we have barely fully explored our ocean?

Question

Basically the title, but I always wondered if the Mariana Trench was the actual deepest point on our planet

In: 56

Answer 1

“Explore” is a vague term.

We haven’t visually inspected every inch of the seabed, but we have mapped most, if not all, of it with sonar.

And we “know” there isn’t a random narrow tunnel in some shallower section that might descend another 10,000 ft because geography doesn’t do that, and it would have collapse or filled in anyway.