A fresh crater caught attention of New Horizons team members as they were studying high-resolution infrared image of Pluto’s largest moon.
This composite image is based on observations from New Horizons’ Ralph/LEISA instrument made on July 14, when the spacecraft was 50,000 miles (81,000 km) from Charon. The data were downlinked October 1 – 4 and processed into a map of Charon’s 2.2 micron ammonia-ice absorption band (green color). Panchromatic images from New Horizons’ Long Range Reconnaissance Imager used as the background in this composite were taken on July 14 and downlinked October 5 – 6. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute.
The newly-discovered crater, named Organa, is about 3 miles (5 km) in diameter.
The crater and the surrounding material ejected from it show infrared absorption at wavelengths of 2.2 microns, indicating that the crater is rich in frozen ammonia (at room temperature, ammonia is a colorless, highly irritating gas with a sharp, penetrating odor).
The infrared spectrum of nearby crater, known as Skywalker, is similar to the rest of moon’s craters and surface, with features dominated by water ice.
“This is a fantastic discovery,” said New Horizons team member Dr Bill McKinnon, a scientist at Washington University in St. Louis.
“We have various ideas when it comes to the ammonia in Organa. The crater could be younger, or perhaps the impact that created it hit a pocket of ammonia-rich subsurface ice,” added team member Dr Will Grundy of Lowell Observatory.
“Alternatively, maybe Organa’s impactor delivered its own ammonia,” he said.
Organa and Skywalker are about the same size, with similar appearances, including bright rays of ejected material.
“Concentrated ammonia is a powerful antifreeze on icy worlds, and if the ammonia really is from Charon’s interior, it could help explain the formation of the moon’s surface by cryovolcanism, via the eruption of cold, ammonia-water magmas,” Dr McKinnon said.
