system
Given the following post, respond as if you're commenting on Reddit:
human
[DC] What could Superman discover about the planet that we don't currently know?

There isn't much of the Earth left unexplored but the places humans can't go pose no problem to Superman.  He could find out what is at the bottom of the Mariana Trench and what the core of the planet is really like.  What else could he find out that remains a mystery to us?
gpt
As you've said, most things on Earth are already explored, so Superman contribution would be about the same that unmanned probes can do - like discovering some extremophile life forms in extreme environments, carving up eternal ice in Arctic and Antarctic to see what's beneath, etc. 

Of course, in DC, Earth has a hole on the pole, where there is a passage/portal into the  Skartaris, supposedly the place at the Earth's core, so there's that to discover too. Well, for the public to discover - adventurers of all kind have visited the place for ages.