The instruments on the James Webb Space Telescope (JWST) can reach some of the farthest corners of the universe in space and time. Occasionally, however, they target places closer to Earth to give humans a different perspective of their stellar neighborhood.
Expanding the inventory. That’s what recently happened. JWST targeted Pluto’s largest moon, Charon, and found evidence of two new compounds on its surface: carbon dioxide (CO2) and hydrogen peroxide (H2O2).
Researchers at the Southwest Research Institute (SwRI) led the project. According to a recent paper published in Nature Communications, the discovery adds new materials to Charon’s “chemical inventory.” Its stock already includes water ice, ammonia-containing compounds, and organic molecules.
“Charon is the only midsized Kuiper Belt object... that has been geologically mapped, thanks to the SwRI-led New Horizons mission,” Silvia Protopapa, a team member responsible for the discovery, said in a press release. “Charon is not obscured by highly volatile ices such as methane and therefore provides valuable insights into how processes like sunlight exposure and cratering affect these distant bodies,” she added.
Near-infrared. Between 2022 and 2023, the telescope targeted the system formed by Pluto and Charon, obtaining complete coverage of the satellite’s northern hemisphere. The JWST’s Near Infrared Spectrograph (NIRSpec) made this discovery possible.
The instrument analyzed the near-infrared portion of the light reflected from Charon. Different elements and molecules leave a distinct imprint on how light reflects off an object’s surface. By analyzing this “siganture,” it’s possible to determine which compounds reflect that light. The wider the range of the light spectrum NIRSpec analyzes, the more data experts have about those compounds.
According to the researchers, the analysis and its comparison with laboratory measurements also concluded that the carbon dioxide on Charon’s surface would form a coating covering a more profound layer with abundant water ice.
“Signatures” in the electromagnetic spectrum of various compounds found on Charon. Image | S. Protopapa, SwRI, NASA, ESA, CSA, STScI, JHUAPL
Where does the CO2 come from? Regarding the origin of this carbon dioxide, the team believes that it could be in the interior of the satellite and that it would have reached the surface through Charon’s cratering processes. “Carbon dioxide is known to be present in regions of the protoplanetary disk from which the Pluto system formed,” Protopapa explained.
Crystalline water? The crystalline water, meanwhile, “clearly” indicates that ultraviolet radiation is affecting the icy water on the satellite’s surface. Charged particles arriving from the Sun and the interstellar medium also influence the formation of hydrogen peroxide. The ions and other particles that hit the water molecules can break them apart, causing their atoms to recombine and form hydrogen peroxide molecules.
A peculiar system. Pluto and Charon form a binary system that, due to the slight difference in mass between the two objects and their distance, orbits around a center of gravity outside Pluto. This means that both orbit around an imaginary point near the dwarf planet.
Knowing Charon’s composition can help scientists understand the mysteries of this unique system, such as how this satellite was born. According to astrophysicist Brad Tucker, the central hypothesis about Charon is that it resulted from an impact between Pluto and an asteroid in the Kuiper belt, a birth similar to that of the Moon.
But this isn’t the only possibility. For example, both objects could have originated from the collision of two other asteroids, which would have disintegrated and reassembled in this binary system. Research like this may help experts solve the mystery.
Image | NASA
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