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Unprecedented discovery on Charon revealed frozen molecules that help investigate how distant worlds formed and evolved in the Kuiper Belt, a region beyond Neptune capable of preserving ancient chemical records of the Solar System’s history.
The James Webb Space Telescope identified frozen carbon dioxide and hydrogen peroxide on the surface of Charon, Pluto’s largest moon, in a discovery published in the journal Nature Communications in 2024.
The detection expands the known chemical inventory of this icy world and provides new data to investigate the formation and evolution of Kuiper Belt bodies.
Obtained through the NIRSpec instrument, the near-infrared spectrograph of the James Webb, the discovery analyzed the light reflected by Charon’s surface in wavelengths reaching 5.2 micrometers.
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This range surpasses the 2.5 micrometer limit of previous observations and allowed for the identification of chemical signals not previously seen on this distant moon.
James Webb identifies frozen compounds on Charon
In Charon’s northern hemisphere, researchers confirmed the presence of the two frozen compounds.
Before this result, observations made from Earth and space had already indicated frozen crystalline water, substances associated with ammonia, and darkened materials similar to tholins, organic compounds produced by prolonged chemical processes.
Classified as an intermediate-sized trans-Neptunian object, Charon also stands out for having geological mapping obtained by the New Horizons mission.
Unlike larger bodies beyond Neptune, such as Pluto, Eris, and Makemake, its surface is not dominated by hyper-volatile ices, which facilitates the reading of chemical signals preserved in the ice.
Due to this characteristic, the moon has become a relevant target for studies on differentiation, radiation, and cratering in the Kuiper Belt.
The analysis of the composition of such surfaces can reveal compounds common in different regions of the solar nebula, the gas and dust environment that gave rise to the Solar System.
Carbon dioxide exposed by impacts in the ice
On Charon, the carbon dioxide detected by James Webb appears in pure crystalline form and possibly mixed with other materials on the surface.
The researchers’ preferred interpretation suggests that the compound originates from the moon’s interior and has been exposed by impacts that created craters in the ice.
Silvia Protopapa, a scientist at the Southwest Research Institute and lead author of the study, stated that this upper layer of carbon dioxide likely came from the interior and was revealed by cratering events.
The researcher also noted that the compound was already known in regions of the protoplanetary disk where Pluto’s system formed.
This interpretation does not make Charon a definitive answer about the origin of planets, but it adds an important piece to the scientific puzzle.
By comparing icy worlds, moons, and small bodies, the composition of the moon helps trace ancient materials preserved in cold regions far from the Sun.
Hydrogen peroxide reveals active chemistry on the surface
In addition to carbon dioxide, the presence of hydrogen peroxide indicates that the surface rich in frozen water undergoes alteration caused by solar ultraviolet light, solar wind particles, and galactic cosmic rays.
This compound forms when water molecules are broken down by ions, electrons, or photons, allowing new combinations between hydrogen and oxygen.
With this result, Charon is no longer just a frozen block preserved since the youth of the Solar System.
Even in an extremely cold and distant region, its surface continues to be slowly modified by radiation, impacts, and chemical interactions accumulated over billions of years.
To compare the signals seen by the telescope, the researchers resorted to laboratory experiments with materials irradiated under conditions similar to those expected on Charon.
Ujjwal Raut, a researcher at the Southwest Research Institute, stated that tests at the CLASSE laboratory helped demonstrate the formation of hydrogen peroxide in mixtures of carbon dioxide and frozen water.
Kuiper Belt holds ancient records of the Solar System
More than the isolated presence of two molecules, the discovery draws attention for the set of processes revealed by them.
While carbon dioxide points to internal or ancient materials exposed by impacts, hydrogen peroxide serves as evidence of the continuous transformation of frozen water by radiation.
The study also reinforces the role of James Webb in investigating small and distant bodies of the Solar System.
Ian Wong, scientist at the Space Telescope Science Institute and co-author of the article, stated that the telescope’s observational capability allowed exploration of the light scattered by Charon’s surface at previously inaccessible wavelengths.
The interpretation presented by the scientists relies on the combination of space observations, spectral models, and laboratory experiments.
Even so, the authors themselves treat some origins of carbon dioxide as possibilities under analysis, without turning scientific hypotheses into absolute certainties.
Charon helps to compare worlds beyond Neptune
Among the medium-sized bodies located beyond Neptune, Charon serves as a reference for comparative studies.
Its surface preserves impact marks, signs of water ice, darkened materials, and compounds produced or revealed by physical processes that may also occur in similar objects of the Kuiper Belt.
Although it does not alone change what science knows about the origin of planets, the discovery offers new data to refine models on the formation of icy worlds.
By revealing previously invisible molecules in Charon, James Webb has shown that distant objects can still hold crucial chemical records to understand the history of the Solar System.
If a frozen moon of Pluto still preserves such ancient and, at the same time, so altered signs by space radiation, what other clues might be hidden in the small worlds beyond Neptune?
