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takyon [soylentnews.org] writes:

A field of mysterious "halo" craters [nasa.gov] has been discovered on Pluto:

The region is far west of the hemisphere NASA's New Horizons spacecraft viewed during close approach last summer. The upper image – in black and white – sports several dozen "haloed" craters. The largest crater, at bottom-right, measures about 30 miles (50 kilometers) across. The craters' bright walls and rims stand out from their dark floors and surrounding terrain, creating the halo effect.

In the lower image, composition data from New Horizons' Ralph/Linear Etalon Imaging Spectral Array (LEISA) indicate a connection between the bright halos and distribution of methane ice, shown in false color as purple. The floors and terrain between craters show signs of water ice, colored in blue. Exactly why the bright methane ice settles on these crater rims and walls is a mystery; also puzzling is why this same effect doesn't occur broadly across Pluto.

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