HEADLAND: It's not Ahch-To. I know it's similar, and it was intentionally supposed to be similar in terms of terrain and feeling isolated and surrounded by water and less lush green and more rocky. But the idea is that cortosis is mined on this planet, so I don't think that's the case with Ahch-To. Part of the reason this is his home base is that cortosis is a very rare metal. I don't think we say it explicitly in the show, but that's a reason it's not Ahch-To.