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Dawn at Ceres reveals mystery features

Since Dawn slid into orbit on March 6, 2015, the spacecraft has found at least 2 mysterious features on Ceres – a dome-shaped mountain and the famous bright spots.

Ahuna Mons, a smooth-sided, dome-shaped mountain on the dwarf planet Ceres.  Scientists still can't explain how it formed.

Ahuna Mons, a smooth-sided, dome-shaped mountain on the dwarf planet Ceres. Scientists still can’t explain how it formed. Image via NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

It’s been a year since NASA’s Dawn spacecraft went into orbit around the dwarf planet Ceres – largest body in the asteroid belt between Mars and Jupiter – and first asteroid ever to be discovered in 1801. Carol Raymond, deputy principal investigator for the mission, based at NASA’s Jet Propulsion Laboratory, Pasadena, California, said that, since it slid into Ceres orbit on March 6, 2015, the spacecraft has:

… defied our expectations and surprised us in many ways.

In a statement this week, these scientists described two mysterious features on Ceres, explored by Dawn. They said that Ceres’ most enigmatic feature isn’t its famous bright spots, but instead a tall mountain that the Dawn team has named Ahuna Mons.

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

As Dawn circled Ceres at increasingly lower altitudes, the shape of this mysterious feature began to come into focus. From afar, Ahuna Mons looked to be pyramid-shaped, but upon closer inspection, the scientists said:

…it is best described as a dome with smooth, steep walls.

Ahuna Mons on Ceres, a mountain about 4 miles (6 kilometres) tall, in a simulated view using NASA’s Dawn spacecraft images. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

Ahuna Mons on Ceres, a mountain about 4 miles (6 kilometres) tall, in a simulated view using NASA’s Dawn spacecraft images. Image via NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

The Dawn scientists say they still can’t explain how it formed.

Dawn’s latest images of Ahuna Mons, taken 120 times closer than in February 2015, reveal that this mountain has a lot of bright material on some of its slopes, and less on others. On its steepest side, it is about 3 miles (5 km) high.

The mountain has an average overall height of 2.5 miles (4 km). It rises higher than Washington’s Mount Rainier and California’s Mount Whitney.

The mysterious mountain Ahuna Mons is seen in this mosaic of images from NASA's Dawn spacecraft. Dawn took these images from its lowest-altitude orbit. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Images from the Dawn spacecraft were used to create this mosaic of the mysterious mountain on Ceres, called Ahuna Mons by scientists. Dawn took these images from its lowest-altitude orbit. Image via NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Scientists are beginning to identify other features on Ceres that could be similar in nature to Ahuna Mons, but none is as tall and well-defined as this mountain.

About 420 miles (670 km) northwest of Ahuna Mons lies the now-famous Occator Crater.

Before Dawn arrived at Ceres, images of the dwarf planet from NASA’s Hubble Space Telescope showed a prominent bright patch on the surface. As Dawn approached Ceres, it became clear that there were at least two spots with high reflectivity.

This representation of Ceres' Occator Crater in false colors shows differences in the surface composition. Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

This representation of Ceres’ Occator Crater in false colors shows differences in the surface composition. Image via NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

As the resolution of images improved, Dawn revealed at least 10 bright spots in this crater alone, with the brightest area on the entire body located in the center of the crater.

In December, 2015, scientists said that the bright spots on Ceres are likely salt deposits.

But they say it’s still not yet clear whether this bright material is the same as the material found on Ahuna Mons. Marc Rayman, Dawn’s chief engineer and mission director at JPL, said:

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. 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.

Researchers will present new images and other insights about Ceres at the 47th Lunar and Planetary Science Conference, during a press briefing on March 22, 2016, in The Woodlands, Texas.

In its recent statement, NASA also pointed out that:

When it arrived at Ceres on March 6, 2015, Dawn made history as the first mission to reach a dwarf planet, and the first to orbit two distinct extraterrestrial targets. The mission conducted extensive observations of Vesta in 2011-2012.

In this closest-yet view, the brightest spots within a crater in the northern hemisphere of the dwarf planet Ceres are revealed to be composed of many smaller spots. Their exact nature remains unknown.  Image via NASA Dawn mission.

The brightest spots within Occator Crater in the northern hemisphere of the dwarf planet Ceres are actually composed of many smaller spots. Image via NASA Dawn mission.

Bottom line: Since Dawn spacecraft began orbiting dwarf planet Ceres a year ago, it has found at least 2 mysterious features – a dome-shaped mountain and the famous bright spots. See images and learn more here.

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Deborah Byrd

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