the last one that New Horizons will see showing those spots.
This is going to keep the planetary geologists busy for a while :)
Those spots remind me of regular geometric patterns I've seen in Alaska and northern Canada, where they're caused by frost upheaval in the tundra soils. I'm not saying that's the cause on Pluto, just that they remind me of it. For one thing, the scale on Pluto is vastly different. The spots on Pluto are 300 miles or so across; the tundra patterns I've seen are 5 to 10 feet across!