With just 15 days to the flyby, New Horizon's LORRI camera has been returning images of variegated terrain on both Pluto and its largest moon Charon. There are light colored terrains which are expected to be nitrogen frost and dark colored terrains that should be organic compounds made from ices by the radiation flux. Pluto has a thin nitrogen atmosphere which develops shifting haze.
Pluto by New Horizons on June 18, 2015. Distance 31 507 424 Km.
A warning though: image deconvolution can produce artifacts. The mottled appearance of Pluto and Charon we are seeing in these images may be exaggerated. To get a better idea of what may really be there (and will be clearly visible in a couple of weeks), it is best to look at raw images, such as this one:
Raw image (not deconvolved) of Pluto and Charon, June 22, 2015. A stacked and sharpened version of four images captured on June 22 from a distance of 26.8 million kilometers. Björn Jónsson says about this image: "The dark feature very near or at Pluto's pole continues to be visible and I continue to suspect it to be a small, dark polar cap. The bright terrain continues to look mottled (which it didn't a few days ago in lower-res images) and these features are probably at least partially real. The dark spot near the right limb at ~(203,354) is definitely a real feature and the brighter spot next to it is probably real as well. Charon is now showing lots of interesting details. In particular the small, 'bright' spot near the center of Charon's disc is a real feature but its brightness relative to the darker terrain is exaggerated here." -- From Emily Lakdawalla's blog
Come below the orange tholin haze for speculations about the dark areas on Pluto.
Many Kuiper Belt Objects (KBOs) have a dark red coloration that is caused by tholins on their surfaces. Tholins are hydrocarbon chains made from methane, ethane and molecular nitrogen by ultraviolet light and charged particle radiation. On Titan, they are made from gases in the upper atmosphere and form an orange haze; heavier molecules rain down onto the surface. On Neptune's moon Triton, and on Pluto and other KBOs, they are formed by radiation acting on surface ices and thin vapor layers. Heterocyclic and polycyclic aromatic molecules may be built up over time. These could include nucleic acids and amino acids.
Terrestrial microbes find tholins delectable, but at the temperatures of Pluto -- where nitrogen freezes -- there are unlikely to be any tiny diners. However, material from the Kuiper Belt was delivered to Earth during Late Heavy Bombardment (ca. 4.1-3.8 billion years ago), so this organic manna might have been on the menu back then.
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