WASHINGTON, March 14 (UPI) -- While reviewing Pluto images captured by the New Horizons probe last summer, scientists noticed what looks like a giant "bite mark" on the surface of the dwarf planet.
Researchers believe the missing chunk of planetary flesh was lost via sublimation, a phase change from solid to gas. As a portion of Pluto's methane ice-rich surface vaporized, a patch of water ice was revealed below.
In the photos a young crater-free stretch of icy plains called Piri Planitia can be seen bordered by cliffs, scarps and mesas to the west and south. A fault line called Inanna Fossa lies to the northeast.
Compositional data collected by New Horizons suggest the plateau to the south of the plains, Vega Terra, is rich in methane ice, while the plains host mostly water ice. Researchers think that as the methane ice sublimates, the cliffs are eroded and retreat southward, leaving behind the freshly exposed plains.
Because Pluto is so cold, the watery plains remain a frozen combination of rock and ice.
"The light/dark mottled pattern of Piri Planitia in the left inset is reflected in the composition map, with the lighter areas corresponding to areas richer in methane -- these may be remnants of methane that have not yet sublimated away entirely," NASA researchers wrote in an update.