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New close-up images of dwarf planet Pluto have ‘scientists reeling’ because of the bewildering variety of surface features revealed.As celestial bodies go, Pluto is far more surprising than anyone could have expected.

“Pluto is showing us a diversity of landforms and complexity of processes that rival anything we’ve seen in the solar system,” said New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute (SwRI) in Boulder, Colorado, in the official Nasa announcement that also claimed scientists were ‘reeling’ from seeing the new pictures.

“If an artist had painted this Pluto before our fly-by, I probably would have called it over the top – but that’s what is actually there,” added Stern.

The surface is a hotch-potch of terrains. Heavily cratered regions sit next to smooth plains, giving planetary geologists a profound puzzle to solve. The number of craters on a world’s surface indicates its age – think of them like scars that accumulate with time as asteroids and meteorites hit the body.

Scientists had expected Pluto to be heavily cratered across its whole globe because no one knows how such a small planet could produce enough heat to melt its surface, erasing the craters, and producing the young looking, smooth plains.

Yet this is exactly what they are seeing must have happened on Pluto. It is just one of many surprises associated with the images and data returned about the world from the flyby.

The new images also add a new mystery to the list: dunes. There are dark features visible that look at first glance like wind-blown dunes. These features too were thought to be impossible before the fly-by.

“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 from Washington University, St Louis, in the official announcement. “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.”New Horizons mission flew past Pluto on 14 July 2015 at an altitude of 12,500km above the unknown surface. All data and images were recorded on board for later transmission to Earth.

These new images are part of a 16-month download that began last weekend. Because New Horizons is so far away, more than five billion kilometres, data trickles back hundreds of thousands of times more slowly than over a fibre optic broadband on Earth.

All images received so far from the spacecraft’s Long Range Reconnaissance Imager (LORRI) instrument have been made immediately available to the public in their raw form here.

Mars also had a new portrait released this week. ESA’s Mars Express spacecraft flew over the red planet’s south pole and returned a picture-perfect view of the Martian ice cap. The bright white ice is composed of water and carbon dioxide.

Captured during Mars’s southern hemisphere summer, the cap is seen at its smallest. During the winter season, the ice extends into the smooth regions that surround it.

Stuart Clark is the author of The Unknown Universe (Head of Zeus). He is teaching the Guardian Masterclass, How the Universe Works in September.