21/04/2016 6:37 PM AEST | Updated 21/04/2016 10:36 PM AEST

NASA Images Reveal Close-Up Look At Mysterious 'Bright Spots' On Dwarf Planet Ceres

The craters are quite unusual.

The “bright spots” on Ceres captured the public's imagination last year when they were first spotted by NASA's Dawn spacecraft as it approached the dwarf planet. Now, the space agency has released a remarkably detailed image of a crater at the heart of one of those bright spots.

And it's a little weird.

While many craters have rounded edges, the 21-mile wide Haulani Crater has a series of sharp angles, making it more of a polygon than a circle: 

An enhanced color view of the Haulani Crater on Ceres taken by NASA's Dawn spacecraft from a distance of 915 miles.

NASA said the crater's unusual shape was due to pre-existing stress fractures in the planet's surface -- not an impact with a giant polygon. The enhanced false-color image showed the material ejected from the crater at impact in shades of blue. 

Scientists said the crater was relatively young. 

"Haulani perfectly displays the properties we would expect from a fresh impact into the surface of Ceres," Martin Hoffmann, co-investigator on the Dawn framing camera team based at the Max Planck Institute for Solar System Research in Göttingen, Germany, said in a news release. "The crater floor is largely free of impacts, and it contrasts sharply in color from older parts of the surface."

NASA also got an up-close look at the Oxo crater, and it's even more unusual. 

Oxo is only 6 miles wide, but it is the second brightest feature on the dwarf planet. It also has a large "slump" in the rim "where a mass of material has dropped below the surface." 

The Oxo crater on Ceres, which has a "slump" in its rim. 

NASA called Oxo a "hidden treasure" and said the materials on the floor of the crater appeared to be different from those elsewhere on Ceres. 

"Little Oxo may be poised to make a big contribution to understanding the upper crust of Ceres," Chris Russell, principal investigator of the mission, said in a news release. 

The nature of the dwarf planet's bright spots were the subject of widespread debate last year. In December, scientists said they believed the bright spots were salt deposits, specifically a type of magnesium sulfate called hexahydrite.

Ceres is located in the asteroid belt between Mars and Jupiter. 

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