The discovery of strange halo-like craters on Pluto has raised a new mystery about how additional scars are formed in the icy world.
Pluto's halo craters are clearly visible in the new NASA New Horizons spacecraft image, which made the world's first fly-around of a dwarf planet in July 2015. The black-and-white image shows dozens of annular craters (NASA describes these formations as “surrounded by a halo”) scattered across the dark landscape of Vega Terra, a region in the far western hemisphere, photographed by the New Horizons during its flight. Craters have bright walls and fringe that makes them stand out from dark surroundings.
While the craters with halos are exciting, the question that really baffles scientists is what these features are made of.
Glimpses in the craters seen by the Ralph Linear Reference Visualizing Spectral Assembly on New Horizons showed an amazing connection between the bright halo characteristics and the distribution of methane ice, explained by NASA staff in the image description. This methane ice around the craters is shown in dark purple in the cut included in the new image. The bottom of the crater, as well as the intermediate regions, meanwhile, is colored blue to show water ice. "Why bright methane settles in the form of ice remains a mystery; it also puzzles why the same effect does not occur everywhere on Pluto," NASA staffers write in the image description.
So this is another puzzle for scientists to ponder while images and data continue to flow from Pluto back to Earth after the July 14 flyby. Mission scientists said that loading the probe data should be completed by October or in November.
The NASA New Horizons spacecraft was launched in 2006 and is currently heading for the Kuiper belt, an area of ice bodies beyond the orbit of Neptune. Last week, mission scientists submitted a proposal to expand the mission, which, if approved, proposes to send a probe to object 2014 MU69 in the Kuiper belt on January 1, 2019.
