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."

pluto close up
This 220-mile (350-kilometer) wide view of Pluto from NASA’s New Horizons spacecraft illustrates the incredible diversity of surface reflectivities and geological landforms on the dwarf planet. The image includes dark, ancient heavily cratered terrain; bright, smooth geologically young terrain; assembled masses of mountains; and an enigmatic field of dark, aligned ridges that resemble dunes; its origin is under debate. The smallest visible features are 0.5 miles (0.8 kilometers) in size. This image was taken as New Horizons flew past Pluto on July 14, 2015, from a distance of 50,000 miles (80,000 kilometers).NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
pluto close up
Mosaic of high-resolution images of Pluto, sent back from NASA’s New Horizons spacecraft from Sept. 5 to 7, 2015. The image is dominated by the informally-named icy plain Sputnik Planum, the smooth, bright region across the center. This image also features a tremendous variety of other landscapes surrounding Sputnik. The smallest visible features are 0.5 miles (0.8 kilometers) in size, and the mosaic covers a region roughly 1,000 miles (1600 kilometers) wide. The image was taken as New Horizons flew past Pluto on July 14, 2015, from a distance of 50,000 miles (80,000 kilometers).NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
pluto close up
This synthetic perspective view of Pluto, based on the latest high-resolution images to be downlinked from NASA’s New Horizons spacecraft, shows what you would see if you were approximately 1,100 miles (1,800 kilometers) above Pluto’s equatorial area, looking northeast over the dark, cratered, informally named Cthulhu Regio toward the bright, smooth, expanse of icy plains informally called Sputnik Planum. The entire expanse of terrain seen in this image is 1,100 miles (1,800 kilometers) across. The images were taken as New Horizons flew past Pluto on July 14, 2015, from a distance of 50,000 miles (80,000 kilometers).NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
pluto close up
In the center of this 300-mile (470-kilometer) wide image of Pluto from NASA’s New Horizons spacecraft is a large region of jumbled, broken terrain on the northwestern edge of the vast, icy plain informally called Sputnik Planum, to the right. The smallest visible features are 0.5 miles (0.8 kilometers) in size. This image was taken as New Horizons flew past Pluto on July 14, 2015, from a distance of 50,000 miles (80,000 kilometers).NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
pluto close up
This image of Pluto’s largest moon Charon, taken by NASA’s New Horizons spacecraft 10 hours before its closest approach to Pluto on July 14, 2015 from a distance of 290,000 miles (470,000 kilometers), is a recently downlinked, much higher quality version of a Charon image released on July 15. Charon, which is 750 miles (1,200 kilometers) in diameter, displays a surprisingly complex geological history, including tectonic fracturing; relatively smooth, fractured plains in the lower right; several enigmatic mountains surrounded by sunken terrain features on the right side; and heavily cratered regions in the center and upper left portion of the disk. There are also complex reflectivity patterns on Charon’s surface, including bright and dark crater rays, and the conspicuous dark north polar region at the top of the image. The smallest visible features are 2.9 miles 4.6 kilometers) in size.NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute