The new snapshot described by Dr. Moore on Friday was near the mountains and likewise devoid of craters, but it was almost flat. The lack of craters indicates that the surface was erased by erosion or tectonic activity in the recent geological past — within the past 100 million years.

“This could be only a week old, for all we know,” Dr. Moore said.

(Craters have been spotted in the global view of Pluto, and other regions could be geologically much older.)

Dr. Moore speculated that the troughs, breaking the plains into irregular shapes 12 to 20 miles across, could be caused by convection of carbon monoxide, methane and nitrogen ices below the surface, “creating the same sort of patterns that you see when you look at the surface of a boiling pot of oatmeal, or like the blobs in a lava lamp.”

Another possibility is that they could be similar to mud cracks on Earth, caused as the soil dries and contracts, Dr. Moore said. The shapes are reminiscent of those seen near the north pole on Mars, but it was too early to tell if similar geological processes had shaped them.