Apart from filling the gap in space environment observation, astronomers are stunned over the new discovery of a field of methane ice craters on Pluto’s surface by NASA’s New Horizons spacecraft.

According to a report by Cosmos, NASA scientists are continuing to receive images and data from the New Horizons spacecraft, months after the probe departed the Plutonian system. The newest discovery is identifying of an area on Pluto covered with “halo” craters, from the latest intriguing batch of photos shows.

The field of craters on Pluto’s surface lies in the far western part of the hemisphere that New Horizons approached closely last summer. These craters are measured to be ranging in size up to 50 kilometers across, have unusually bright edges, making them appear as bright halos scattered over a darker landscape.

Spectral analysis of the region reveals that the bright parts of the crater-strewn area are composed of both methane ice and water ice. The water ice is found mostly in the crater floors and surrounding terrain while the crater walls appear to be made of methane ice.

Scientists studying Pluto have noted that methane ice has not been seen to settle on crater rims and walls anywhere else on Pluto. The reason for the methane ice distribution among the halo craters is a mystery.

NASA reports that New Horizons imaged the crater field, located within the informally named Vega Terra region, on July 14, 2015. New Horizons’ Ralph/Linear Etalon Imaging Spectral Array (LEISA) collected the spectral composition data while the probe’s Long Range Reconnaissance Imager (LORRI) captured the low- and high-resolution images that NASA used to create a composite photo.

The high-resolution image and composition data were collected when New Horizons was about 28,000 miles above the surface. New Horizons will continue to send its collected data back to Earth for analysis.