This incredible mosaic of images from NASA’s Dawn orbiter shows one of Ceres’ most intriguing features — a mysterious mountain called Ahuna Mons.

Ahuna Mons has an average overall height of 2.5 miles (4 km). On its steepest side, it is approximately 3 miles (5 km) high. And its diameter is 12 miles (20 km).

The mountain appeared as a small, bright-sided bump on the surface of Ceres as early as February 2015 from a distance of 29,000 miles (46,000 km), before Dawn was captured into orbit.

As the spacecraft circled the dwarf planet at increasingly lower altitudes, the shape of Ahuna Mons began to come into focus.

From afar, this mountain looked to be pyramid-shaped, but upon closer inspection, it is best described as a dome with smooth, steep walls.

“No one expected a mountain on Ceres, especially one like Ahuna Mons. We still do not have a satisfactory model to explain how it formed,” said Dawn science team member Dr. Chris Russell, from the University of California, Los Angeles.

The latest high-resolution images of Ahuna Mons from Dawn reveal that this mountain has a lot of bright material on some of its slopes, and less on others.

The spacecraft took these images from its low-altitude mapping orbit, 240 miles (385 km) above the surface of Ceres, several months ago.

“Ceres has defied our expectations and surprised us in many ways, thanks to a year’s worth of data from Dawn,” said Dawn science team member Dr. Carol Raymond, a scientist at NASA’s Jet Propulsion Laboratory.

“We are hard at work on the mysteries the spacecraft has presented to us.”