This will be our final view of Pluto’s Charon-facing hemisphere for decades to come. It’s the one that hosts a remarkable series of four, evenly-spaced dark patches. They remind me of puzzle pieces, an apt comparison since so much about Pluto is still a puzzle. We first saw the inky blobs in photos returned by New Horizons in late June, when they looked almost too perfect to be real.
Now we can see that each has a unique texture and shape, and at least two are connected via narrow, snaky “channels”. “We can’t tell whether they’re plateaus or plains, or whether they’re brightness variations on a completely smooth surface,” said Jeff Moore of NASA’s Ames Research Center in press release last night. All together the quad spots span some 300 miles (480 km) across or about the distance between Minneapolis, Minn. and Milwaukee, Wis. or the size of the state of Missouri.
This side of the globe won’t be seen close up again if and when we send another probe Pluto’s way. Instead, when New Horizons makes its closest approach to Pluto early Tuesday morning Eastern Time, it will focus on the opposing or “encounter hemisphere” of the dwarf planet. Because Pluto rotates once on its axis in 6.4 days, the four-spot hemisphere will be off to one side by Tuesday and not in view. If Pluto rotated faster, say once every day, we’d be able to see the spots come round two more times before the encounter.
Sorry Charlie, only one hemisphere up close during this visit. On the morning of July 14, New Horizons will pass about 7,800 miles (12,500 km) from the face with a large heart-shaped feature and the dark “whale” positioned along the equator. Scientists will use what we learn in detail from that side of Pluto to make sense of other parts of the dwarf planet that won’t be seen in detail.
Other features visible in the latest image are polygonal or multi-sided geometrical shapes and hints of craters. Charon’s starting to look pretty spotty, too!