They are the best planets. Usually the ones filled with Graviton Balls.
Took a while to get sorted out. Have my toxic gear, although it needs a lot of zinc to keep it powered. I was wandering around on the surface picking up the odd Graviton Ball, but picking one up instantly triggers an Elite sentinel attack :S
After exploring a bit more I tracked down the trading post. Had a mooch about and literally hit the motherlode. A huge cave network a few hundred metres from the trading post that is rammed full of Vector Cubes, tripping over them everywhere Picking them up in cave systems means no environmental stuff to deal with, and the sentinels don't bother you, perfect.
Going to rinse this cave system dry. The trading post is one of the big ones with lots of ships coming and going so I'm keeping my eye out for a beaut