The most recent and enigmatic visitor to our cosmic neighborhood has begun to transform its appearance before the lenses of the most powerful telescopes on Earth.
Researchers at the National Science Foundation (NSF), operating the Gemini North telescopehave detected a significant change in the interstellar comet 3I/ATLAS: The object, which previously displayed a reddish hue, now glows a deep green color.
This chromatic change is not a sign of extraterrestrial activity or little green menbut a direct consequence of space chemistry.
Interstellar Comet 3I/ATLAS over Egypt’s Black Desert Photo:Instagram @osama.fathi.nsw
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According to a statement from NSF NOIRLabthe person responsible for this glow is diatomic carbon (C2), a molecule composed of two carbon atoms that, when released and excited by sunlight, emits this characteristic color.
The phenomenon is fascinating to astronomers because it reveals that the comet’s composition is actively reacting to the heat of our star. When the Gemini South telescope observed the object in late August, months before its current approach, 3I/ATLAS looked distinctly redder.
What remains unknown is how the comet will behave as it leaves the Sun’s vicinity and cools.
NOIRLab representativesAnnouncement
This transition from red to green is physical evidence that the comet’s nucleus is heating up and releasing new molecules into space, offering fresh clues about its mysterious internal structure.
Although the green color is striking, It is not exclusive to this interstellar traveler. Many comets native to our own solar system exhibit a similar hue when activated under solar radiation. Recent examples include the cometa 12P/Pons-Brooksnicknamed “Mother of Dragons”, and the newly discovered C/2025 F2 (SWAN).
This image shows the halo of gas and dust, or coma, surrounding comet 3I/ATLAS. Photo:NASA/Goddard/LASP/CU Boulder
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A very special comet
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3I/ATLAS occupies a special place in the history of modern astronomy as the third interstellar object identified, following in the footsteps of 1I/’Oumuamua y 2I/Borisov.
Detected at the end of June, it travels to a dizzying speed estimated at 210,000 kilometers per hour. Its hyperbolic, U-shaped trajectory indicates that this is a one-time visit: once it crosses our system, it will never return.
The scientific community agrees that it is probably the largest interstellar object and old observed to date.
Despite viral theories suggesting it could be alien technology, the vast majority of space agencies and astronomers They agree that it is a typical comet, although with intriguing characteristics such as large jets facing the Sun and signs of having been irradiated for billions of years in deep space.
Next December 19 will mark the comet’s closest point to Earth, passing at a safe distance of 270 million kilometers. However, Scientists remain alert to possible surprises in their behavior.
Comet 3I/Atlas will reach its closest point to Earth on December 19. Photo:On / iStock
“What remains unknown is how the comet will behave as it leaves the vicinity of the Sun and cools,” NOIRLab representatives wrote in the statement. “Many comets have a delayed reaction to experiencing heat from the Sun because of the time it takes for the heat to make its way through the comet’s interior. A delay can trigger the evaporation of new chemicals or trigger a cometary outburst.”
Dozens of observatories and spacecraft continue to monitor 3I/ATLAS. Studying it in depth could reveal unpublished details about the borders of our galaxy and about how some of the oldest star systems in the Milky Way formed.
*Article developed with AI support and reviewed by a journalist.
