Pluto continues to be a remarkably curious world. In the latest images from New Horizons, we can see craters surrounded by a white "halo effect" in the western Vega Terra region of the dwarf planet.
The bright halo effect is due to methane ice on the walls and rims of these craters, although why it forms there is a bit of a mystery. This is mirrored in the composition data from another of New Horizons' instruments – the Linear Etalon Imaging Spectral Array (LEISA), which is the purple/blue image below.
In the LEISA image, we see bright methane ice (in purple) on the walls and rims of water ice (in blue) scattered around the craters and terrain. Aside from the methane ice mystery, it's also not clear why this effect is only present in this region and not across the whole of Pluto.
The halo craters are seen on top, with their composition (in false color) below. NASA/JHUAPL/SwRI