At first glance, it looks like a pile of excavated material from the crater beside it, much like a trench dug in a child’s sandbox. But when you realize the pile of material is actually 3 miles high and on the surface of dwarf planet Ceres, the scene becomes quite mysterious.

PHOTOS: Dwarf Planet’s Weirdly Mysterious Surface Mapped

Imaged by NASA’s Dawn mission that is orbiting Ceres in the Main Asteroid Belt, this is the clearest-yet observation of a feature that mission scientists are having a hard time explaining. Called Ahuna Mons by the team (that was once dubbed “Lonely Mountain”), this mountain is bigger than Washington’s Mount Rainier and California’s Mount Whitney and from afar looked like a pyramid.

Dawn is now orbiting Ceres at its lowest mapping orbit of only 240 miles and Ahuna Mons’ intricate features have snapped into focus. It is no longer a pyramid, it is a dome, but clues as to how it formed and why it took this shape are elusive. This mosaic of high-resolution pictures were captured in December and they show the mountain’s steep, smooth sides streaked with bright material.

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

PHOTOS: Our Dwarf Planet Dreams are Coming into Focus

The now-famous Occator Crater lies some 420 miles northwest of Ahuna Mons, a huge impact crater that is speckled with bizarre white patches that have, so far, also eluded a satisfactory explanation. It’s possible that the bright features on the slopes of Ahuna share a common source as Occator’s white spots and it is hoped that now Dawn is so close to Ceres’ surface, these questions may soon be answered.

“Dawn began mapping Ceres at its lowest altitude in December, but it wasn’t until very recently that its orbital path allowed it to view Occator’s brightest area,” said Marc Rayman, Dawn’s chief engineer and mission director at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “This dwarf planet is very large and it takes a great many orbital revolutions before all of it comes into view of Dawn’s camera and other sensors.”

Exactly a year ago, on March 6, 2015, Dawn arrived in Ceres orbit, continuing its historic explorations of the asteroid belt between the orbits of Mars and Jupiter. Having already explored massive asteroid (and protoplanet) Vesta from 2011 to 2012, Dawn slowly powered its way to Ceres, its second orbital objective. The mission has transformed our view of this region of the solar system, revealing the genesis and evolution of planets, highlighting some intriguing mysteries along the way.

ANALYSIS: NASA: We Need YOUR Help to Solve Ceres Mystery

“Ceres has defied our expectations and surprised us in many ways, thanks to a year’s worth of data from Dawn. We are hard at work on the mysteries the spacecraft has presented to us,” said Carol Raymond, deputy principal investigator for the mission also based at JPL.

Source: JPL