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

We aren’t sure. It’s the deepest we’ve found, and we’re assisted by satellites when doing so, but there could absolutely be a non-direct depth (through a cave system, for example) that goes deeper. A direct dive is less likely, because satellites