My recollection is that the briefing map shows the equatorial trench (let's call that running west-east although it's arbitrary I agree) and the trench they go

My recollection is that the briefing map shows the equatorial trench (let's call that running west-east although it's arbitrary I agree) and the trench they go down being perpendicular to that. check out https://youtu.be/TOgtj00Rp8s?si=2E5SieRc8-XMzUU5&t=20 https://youtu.be/TOgtj00Rp8s?si=2E5SieRc8-XMzUU5&t=20 (you may have to scrub back and forward a bit to convince yourself either way). The sphere rotates and you see the big equatorial trench and highlights a smaller trench perpendicular to that that doesn't extend the whole way around. The briefing zooms in to show more detail. That's the one they are going to go down.