NASA's New Horizons spacecraft began its historic journey to Pluto in 2006 and covered 3 billion miles for almost a decade to reach it. This week - as it undertakes a flyby - the deep- space probe has began sending high resolution images of the dwarf planet (including its largest moon, Charon) back to Earth for the first time. The photographs, which was taken from a distance of 7,800 miles, reveal new information that has astonished experts.

Scientists are perplexed with the images showing Pluto's surface, with some branding it as complex. This is because they include landscapes dominated by nitrogen ice flows as well as geographical formations such as mountains, craters and ridges. There are also land features that resemble wind-swept dunes.

"Seeing dunes on Pluto - if that is what they are - would be completely wild, because Pluto's atmosphere today is so thin," said William McKinnon, a researcher from the Geology, Geophysics and Imaging team working for New Horizons, according to an RT report. "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."

The diverse surface features are surprising for many experts because they are unexpected for an object so far from the sun. It is widely believed that Pluto cannot support the geological processes that created such features in other planets, according to Ars Technica. In addition to mountains, craters and glaciers, there are other terrains that indicate a highly diverse environment such as the presence of sweeping plains that suggest a recent remodelling of the planet's surface, Ars Technica said.

NASA is still awaiting another batch of images that could help scientists understand Pluto better. Also, the New Horizons spacecraft still has plenty of fuel and there is a presently lively debate at NASA as to where the space probe will be sent next, in a report by PC.