These optional rules are left to GM discretion per the book's guidance.
Options
Use strict Campaign Operations temperature math. Without this, temperatures are balanced toward more variety (Medium is more common). Turn this on for RAW rules-as-written results.
Uninhabitable terrestrials can have surface water if conditions allow (gravity ≥ 0.5G, atmosphere present, temp ≤ 323K). Per Campaign Ops p.115 "Water, Water Everywhere" optional rule.
When enabled you'll see the internal roll numbers and habitability modifier breakdowns.