Among the fascinating features on dwarf planet Ceres is an intriguing mountain protruding from a relatively smooth area. Scientists estimate that this structure rises about 5km above the surface. Nasa's Dawn spacecraft took this image from an altitude of 4,400km NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Dwarf planet Ceres continues to puzzle scientists throwing more mysteries as spacecraft Dawn zooms in. This time, it is a pyramid-shaped peak towering over a relatively flat landscape that has scientists and amateurs agog.

The steep cone rises about 5km above the surrounding landscape and belies any explanation.

Terrestrial mountains are the product of volcanoes or plate tectonics, while the ones on Moon and Mars came into being at the centres of craters formed by meteorite impacts.

The mountain on Ceres doesn't fit in any of these descriptions.

Ceres has numerous craters of varying sizes, many with central peaks with evidence of past activity including flows, landslides and collapsed structures.

But the 'pyramid mountain' stands on flat land.

Some suggestions are that the edge of the crater it possibly occupies has been smoothened by geyser deposits from below the surface.

More will be revealed as Dawn approached Ceres closer still in August when it will be 1450km from the surface.

Currently it orbits at about 4,400km above Ceres.

"The surface of Ceres has revealed many interesting and unique features. For example, icy moons in the outer solar system have craters with central pits, but on Ceres central pits in large craters are much more common. These and other features will allow us to understand the inner structure of Ceres that we cannot sense directly," said Carol Raymond, deputy principal investigator for the Dawn mission, based at Nasa's Jet Propulsion Laboratory in Pasadena, California.

Ice or salt

The latest images of the asteroid also show more details of the mysterious bright spots at the bottoms of several craters.

The brightest spots located inside a crater have been resolved to reveal at least eight distinct points of light.

Dawn's visible and infrared mapping spectrometer can identify specific minerals present on Ceres by studying the reflected light spectra. This will determine if the spots are made of salt or ice or some other mineral.

Ceres shows more remnants of activity than the protoplanet Vesta, which Dawn studied intensively for 14 months in 2011 and 2012.

Dawn is the first mission to visit a dwarf planet, and the first to orbit two distinct solar system targets. It studied giant asteroid Vesta for 14 months in 2011 and 2012, and arrived at Ceres on 6 March 2015.

When Dawn approaches Ceres even closer in August, at 1,450km from the surface, it will be able to reveal more about the bright spots detected on the asteroid NASA/JPL-Caltech/UCLA/MPS/DLR/IDA