Astronomers have observed carbon dioxide and hydrogen peroxide on the icy surface of Charon, Pluto’s largest moon, thanks to the James Webb Space Telescope. These findings enhance our understanding of Charon’s chemical composition, which already includes water ice, ammonia compounds, and organic materials that give Charon its gray and red hues.
A team led by the Southwest Research Institute has identified carbon dioxide and hydrogen peroxide for the first time on Charon’s frozen surface using the James Webb Space Telescope. This adds to the known chemical profile of Charon, which already includes water ice, ammonia compounds, and the organic materials that contribute to its gray and red colors.
“Charon is the only midsized object in the Kuiper Belt, measuring between 300 and 1,000 miles in diameter, that has undergone geological mapping, thanks to the New Horizons mission led by SwRI, which flew past the Pluto system in 2015,” mentioned Dr. Silvia Protopapa from SwRI, the lead author of a recent paper published in Nature Communications and a co-investigator of the New Horizons mission. “Unlike many larger Kuiper Belt objects, Charon’s surface is clear of highly volatile ices such as methane, allowing us to gain valuable insights into how factors like sunlight exposure and cratering influence these distant bodies.”
The Webb telescope is incredibly well-suited for a detailed study of Charon and other icy objects located beyond Neptune. In 2022 and 2023, the team utilized Webb’s Near-Infrared Spectrograph to conduct four observations of the Pluto-Charon system, achieving comprehensive coverage of Charon’s northern hemisphere.
“Webb’s advanced observational capabilities made it possible for our team to investigate the light reflected from Charon’s surface at longer wavelengths than previously feasible, enhancing our understanding of this intriguing object,” stated Dr. Ian Wong, a staff scientist at the Space Telescope Science Institute and co-author of the paper.
The extended wavelength analysis from Webb’s measurements indicates the presence of carbon dioxide. The researchers compared these spectroscopic observations with lab measurements and intricate spectral models of Charon’s surface, concluding that carbon dioxide primarily exists as a thin layer on top of a water ice-rich subsurface.
“We believe that the upper layer of carbon dioxide comes from below the surface and has become exposed through impacts. Carbon dioxide is known to exist in areas of the protoplanetary disk where the Pluto system originated,” Protopapa explained.
The detection of hydrogen peroxide on Charon’s surface suggests that solar ultraviolet light and high-energy particles from solar wind and cosmic rays are altering the water ice-rich surface. Hydrogen peroxide is formed from hydrogen and oxygen atoms that result from the breakdown of water ice due to incoming ions, electrons, or photons.
“Laboratory experiments at SwRI’s CLASSE (Center for Laboratory Astrophysics and Space Science Experiments) were crucial for showing that hydrogen peroxide can form even when carbon dioxide and water ice are mixed under conditions similar to those found on Charon,” said Dr. Ujjwal Raut from SwRI, who leads the CLASSE lab and is the second author of the paper.
This research highlights the unparalleled capability of the Webb telescope to reveal complex surface features shaped by impact and radiation processes.
“The new findings were enabled by the combination of Webb observations, spectral modeling, and laboratory experiments, and these insights could also apply to other midsized objects beyond Neptune,” Protopapa added.
