Scientists reported new findings in mid-December 2025. They are watching an interstellar comet named 3I/ATLAS. This comet is not from our Solar System. It is now showing a faint green glow. It has also been seen in X-rays for the first time.
Teams from ESA, NASA, and the Gemini North Observatory shared these updates. Comet 3I/ATLAS is only the third known object from another star system to visit us. It follows 1I/‘Oumuamua and 2I/Borisov. This comet was not made around our Sun. It is not bound by the Sun’s gravity. It will leave our Solar System forever. Scientists are using many telescopes to study it quickly.
The comet is moving away from the Sun. But heat still reaches it. This causes the comet to release gas and dust. The material forms a cloud called a coma. New observations show the gases in the coma are changing. This creates new colors and light emissions. Scientists are using optical, infrared, and X-ray data together. This helps them understand what this interstellar visitor is made of.
The Comet’s Green Glow Shows Changing Gases
New pictures from the Gemini North telescope show the comet’s green light. The photos were taken on November 26, 2025. The comet had just reappeared from behind the Sun.
Researchers say the green color comes from gas. The comet releases this gas as it heats up. Reports say the green light likely comes from diatomic carbon, or C₂. This gas glows green when energized by sunlight. A Gemini researcher said this green glow is common in many comets. This includes comets from our own Solar System.
Earlier, the comet looked redder. Scientists say the color change is important. It means the mix of dust and gas has changed over time. NASA notes that comets react slowly to the Sun’s heat. One report stated, “thermal effects can take weeks to reach deeper layers of ice.” As new layers warm, different frozen materials turn to gas. This can continue even after the comet’s closest pass by the Sun. The current green glow means 3I/ATLAS is still active. It is still releasing new material as it travels away.
X-Ray Detection Provides New Chemical Clues
ESA made another big announcement. The XMM-Newton space telescope detected the comet in X-rays. This happened on December 3, 2025. The telescope watched the comet for almost 20 hours. The comet was about 280 million kilometers away.
ESA explains how comets can emit X-rays. Gas flowing from the comet interacts with charged solar wind particles. This process is known and seen in other comets. It creates low-energy X-rays only detectable from space.
X-ray observations are very useful. They let scientists study gases that are hard to see with other telescopes. This includes light molecules like hydrogen and nitrogen. These gases are key to understanding how comets form and what they carry.
NASA emphasizes that different telescopes work together. “No single telescope can tell the whole story,” one statement said. By combining X-ray data with infrared data from the James Webb Space Telescope, scientists can compare this interstellar comet to our own.
The chance to study this comet is ending soon. 3I/ATLAS will leave the Solar System for good. An ESA scientist called it “a rare chance to study material from another star system before it is gone.”
