This July 14, 2015 photo released by NASA on Thursday, Sept. 17, 2015 shows the atmosphere and surface features of Pluto, lit from behind by the sun. It was made 15 minutes after the New Horizons' spacecraft's closest approach.
In this small section of the larger crescent image of Pluto, the setting sun illuminates a fog or near-surface haze, which is cut by the parallel shadows of many local hills and small mountains. The image was taken from a distance of 11,000 miles (18,000 kilometers), and the width of the image is 115 miles (185km)
Images downlinked in the past few days have more than doubled the amount of Pluto's surface seen at resolutions as good as 400 metres per pixel.
'The surface of Pluto is every bit as complex as that of Mars,' said Jeff Moore, leader of the New Horizons Geology, Geophysics and Imaging (GGI) team at Nasa's Ames Research Center in Moffett Field, California.
'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.'
New images also show the most heavily cratered, and oldest, terrain yet seen by New Horizons on Pluto next to the youngest, most crater-free icy plains.
There might even be a field of dark wind-blown dunes, among other possibilities.
'Seeing dunes on Pluto - if that is what they are - would be completely wild, because Pluto's atmosphere today is so thin,' said William B. McKinnon, a GGI deputy lead from Washington University, St. Louis. '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.'
Discoveries being made from the new imagery are not limited to Pluto's surface.
Better images of Pluto's moons Charon, Nix, and Hydra will be released Friday at the raw images site for New Horizons' Long Range Reconnaissance Imager (LORRI), revealing that each moon is unique and that big moon Charon's geological past was a tortured one.
Images returned in the past days have also revealed that Pluto's global atmospheric haze has many more layers than scientists realised, and that the haze actually creates a twilight effect that softly illuminates nightside terrain near sunset, making them visible to the cameras aboard New Horizons.
'This bonus twilight view is a wonderful gift that Pluto has handed to us,' said John Spencer, a GGI deputy lead from SwRI.
'Now we can study geology in terrain that we never expected to see.'
The New Horizons spacecraft is now more than 3 billion miles (about 5 billion kilometers) from Earth, and more than 43 million miles (69 million kilometers) beyond Pluto.
The spacecraft is healthy and all systems are operating normally.
Earlier this month Nasa revealed a new animation of New Horizon's mission to Pluto lets you ride shotgun with the probe as it passes the dwarf planet.
New Horizons completed its near decade-long journey to Pluto in July, with a historic flyby that captures the best images ever seen of the icy world.
Nasa has now collected these images into a mesmerising 23-second video, showing the flyby from the spacecraft's point of view.
During its closest approach, the spacecraft came to within 7,800 miles (12,500km) of Pluto's icy surface, travelling at 30,800 mph (49,600 km/h).
The video includes a pass showing the atmospheric glow of Pluto lit by the sun and a look at Charon, Pluto's largest moon.
shed new light on Pluto’s mountains, glaciers and plains.
'This animation, made with real images taken by New Horizons, begins with Pluto flying in for its close-up on July 14,' Nasa writes on the video description.