Pluto's atmosphere might be more complex than we thought. New Scientist claims that scientists think these images could actually show individual clouds floating above the surface of the planet. The magazine claims to have seen emails sent between researchers discussing the formation of clouds above Pluto. One snippet from an email sent by John Spencer of the Southwest Research Institute in Boulder, Colorado reads:
In the [above] image an extremely bright low altitude limb haze above south-east Sputnik on the left, and a discrete fuzzy cloud seen against the sunlit surface above Krun Macula (I think) on the right.
There's no mention of what the clouds might contain, nor any official statement yet about them. That makes it likely that the academics are still working out whether they're the real deal. You can see another example, circled on the left in the image below.
Indeed, in the emails seen by New Scientist there seems to be some deliberation about what constitutes a cloud as opposed to atmospheric haze. The magazine points out that Alan Stern, the leader of the New Horizons mission, wrote that "one way to think of it is that clouds are discrete features, hazes widespread".
What's needed, perhaps, is more data. But because of New Horizons' awfully slow 1-2 Kbps data transfer speed, over half of its captured data is yet to be returned to Earth. It seems it can't arrive soon enough.
Images by NASA/JHUAPL/SwRI