Webb telescope detects CO2 on Charon, Pluto’s largest moon

Oct. 1 () –

Observations of the James Webb Space Telescope have detected carbon dioxide and hydrogen peroxide for the first time on the icy surface of Pluto’s largest moon, Charon.

These discoveries add to Charon’s known chemical inventory, previously identified through ground-based and space-based observations, which includes water ice, ammonia-containing species, and the organic materials responsible for the gray and red coloration of Charon.

“Charon is the only medium-sized Kuiper Belt object, in the range of 300 to 1,000 miles in diameter (500 to 1,600 km), that has been geologically mapped, thanks to the SwRI-led New Horizons mission, which flew by the Pluto system in 2015,” he said in a statement Dr. Silvia Protopapa of SwRI (Southwest Research Institute), lead author of a new Nature Communications paper and co-investigator of the New Horizons mission.

“Unlike many of the larger Kuiper Belt objects, Charon’s surface is not obscured by highly volatile ices such as methane and therefore provides valuable information about how processes such as sunlight exposure and crater formation affect these distant bodies.”

In addition to the more distant universe, the Webb telescope enables detailed exploration of icy bodies in the region beyond Neptune’s orbit. In 2022 and 2023, the team used the Webb Near-Infrared Spectrograph to obtain four observations of the Pluto-Charon system. Different viewing geometries provided complete coverage of Charon’s northern hemisphere.

“Webb’s advanced observation capabilities allowed our team to explore light scattered from Charon’s surface at longer wavelengths than previously possible, expanding our understanding of the complexity of this fascinating object,” said Dr. Ian Wong, staff scientist at the Space Telescope Science Institute and co-author of the paper.

The extended wavelength coverage of Charon’s measurements with Webb reveals signatures of carbon dioxide. The team compared the spectroscopic observations with laboratory measurements and detailed spectral models of the surface, and concluded that Carbon dioxide is present primarily as a surface layer on top of a subsurface rich in water ice.

“Our preferred interpretation is that the upper layer of carbon dioxide originates from the interior and has been exposed to the surface through cratering events. Carbon dioxide is known to be present in regions of the protoplanetary disk from from which the Pluto system was formed,” Protopapa said.

The presence of hydrogen peroxide on the surface of Charon clearly indicates that the water ice-rich surface is altered by solar ultraviolet light and the energetic particles of the solar wind and galactic cosmic rays. Hydrogen peroxide is formed from oxygen and hydrogen atoms that originate from the breakdown of water ice due to the entry of ions, electrons or photons.

“Laboratory experiments conducted at SwRI’s CLASSE (Center for Laboratory Astrophysics and Space Sciences Experiments) facilities were instrumental in demonstrating that hydrogen peroxide can form even in mixtures of carbon dioxide and water ice under conditions analogous to those of Charon“said Dr. Ujjwal Raut of SwRI, leader of the CLASSE laboratory and second author of the paper.

The team’s research shows the Webb telescope’s unrivaled ability to uncover complex surface signatures shaped by impacts and irradiation processes.

“The new insights were made possible by the synergy between Webb observations, spectral modeling and laboratory experiments and possibly “are applicable to other similar medium-sized objects beyond Neptune.”said Protopapa.