Incredible up-close images of Pluto have been returned by the New Horizons spacecraft, showing a "bewildering variety" of surface features. Nasa released the images showing plains, mountains and valleys with a resolution as good as 400m per pixel.

Alan Stern, New Horizons principal investigator, said: "Pluto is showing us a diversity of landforms and complexity of processes that rival anything we've seen in the solar system. If an artist had painted this Pluto before our flyby, I probably would have called it over the top — but that's what is actually there."

New features revealed have left scientists "reeling" from their range of complexity, Nasa said. Jeff Moore, leader of New Horizons Geology, Geophysics and Imaging (GGI) team, said: "The surface of Pluto is every bit as complex as that of Mars. The randomly jumbled mountains might be huge blocks of hard water ice floating within a vast, denser, softer deposit of frozen nitrogen within the region informally named Sputnik Planum."

The images show Pluto's global atmospheric haze has far more layers than scientists previously realised, with the haze creating a twilight effect softly illuminating the night-side terrain at sunset. "This bonus twilight view is a wonderful gift that Pluto has handed to us," said John Spencer, deputy leader of the GGI. "Now we can study geology in terrain that we never expected to see."

The pictures also show the oldest and most heavily cratered terrain next to the youngest icy plains, raising many possibilities about the dwarf planet. William B McKinnon, also GGI deputy lead, said: "Seeing dunes on Pluto - if that is what they are - would be completely wild, because Pluto's atmosphere today is so thin. Either Pluto had a thicker atmosphere in the past, or some process we haven't figured out is at work. It's a head-scratcher."