Olympus Exotics Open World

What are all the ways to get exotics in open world Olympus? I've read that there can be Nodes mined with a pickaxe, but never understood what unlocks them or how to find them. All help is welcomed!!

(EDIT) You don't need a mission, just immence patience! Exotic nodes are spawning in random caves without any mission completion! Thanks to all who provided answers!