The plan area (top right) is free of any of the impact craters visible around it
The latest image, from the centre of Pluto’s "heart feature", show the plains’ enigmatic cellular pattern as well as unusual clusters of small pits and troughs (from lower left to upper right in the picture).
But the high-resolution image has shown no evidence of even any small impact craters, which riddle the surface of the rest of Pluto.
Scientists believe this area, informally known as Sputnik Planum, is composed of volatile ices such as solid nitrogen.
The puzzling patterns and pits on the plain
They theorize the pits and troughs, which are typically hundreds of meters across and tens of meters deep, are possibly formed by sublimation or evaporation of these ices.
However, the reasons for the striking shapes and alignments of these features are a mystery.
A Nasa spokesman said: "Adding to the intrigue is that even at this resolution, no impact craters are seen, testifying to the extreme geologic youth of Sputnik Planum."
Hal Weaver, New Horizons project scientist with Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, said: "Pluto is weird, in a good way.
“The pits, and the way they’re aligned, provide clues about the ice flow and the exchange of volatiles between the surface and atmosphere, and the science team is working hard to
understand what physical processes are at play here.”
The pictures being sent back by the Nasa New Horizons unmanned space probe will send back more higher resolution images over coming months after the close fly by in July.
The smooth plain area is clearly visible on this full picture of Pluto
An alien hunter claims to have found a spaceship (ringed) in Nasa Pluto image
Adding to the intrigue is that even at this resolution, no impact craters are seen, testifying to the extreme geologic youth of Sputnik Planum.
Scott C Waring posted to website UFOsightingsdaily.com that he could see a "space shuttle-like craft" and added a picture with the object ringed.
Sceptics brand these "discoveries" a case of pareidolia when the eyes trick the brain into seeing familiar objects in patterns or texture like a rocky surface.
The New Horizons team described a wide range of findings about the Pluto system so far in its first science paper, just released.
“The Pluto System: Initial Results from its Exploration by New Horizons,” led by mission Principal Investigator Alan Stern, appeared as the cover story in the Oct. 16 issue of Science, just three months after NASA’s historic first exploration of the Pluto system in July.
New Horizons spacecraft reached a distance of 7,750 miles from Pluto’s surface during its July 14 closest approach, gathering so much data it will take almost another year to return to Earth.
The latest close ups of Pluto's biggest moon Charon show its numerous craters
The data returned so far show a surprisingly wide variety of landforms and terrain ages on Pluto, as well as variations in colour, composition and surface reflectivity.
Team members also discovered evidence for a water-ice rich crust, multiple haze layers above the surface in Pluto’s atmosphere, and that Pluto is somewhat larger and a bit more ice rich than expected.
“We were also taught important lessons by the degree of geological complexity that both Pluto and its large moon Charon display.”