Not long after leaving Explorer's Anchorage for Beagle Point in DW2, I came across a system with five Water Worlds. I only had a chance to sell the data for it a few days ago at Colonia and after some digging through screenshots for the system name was delighted to find I had the First Discoveries on them. I had mapped everything in the system and earned nearly 16 million credits. Well worth the time spent mapping the system. :-)