Images captured during the total lunar eclipse on September 7, 2025, have revealed a strange green glow emanating from the interstellar comet 3I/ATLAS. This phenomenon has intrigued scientists, as comets typically exhibit a green hue when they release vapor. However, the situation with 3I/ATLAS appears to be more complicated. Current observations indicate a surprising scarcity of dicarbon (C2) molecules, which are usually responsible for this characteristic glow.
The recent observations were made by astrophotographers Gerald Rhemann and Michael Jäger in Namibia. They documented a blue-green gas coma measuring approximately 2.5 arcminutes across. A short tail was also noted on September 9, further highlighting the comet’s dynamic behavior as it approaches the Sun.
As comets near the Sun, the ices surrounding their rocky nuclei begin to sublime, transforming into a gas atmosphere known as a coma. Solar radiation triggers these gas molecules to fluoresce, producing light across various wavelengths. The James Webb Space Telescope (JWST) has previously identified that 3I/ATLAS possesses an unusual chemical composition, with higher than typical proportions of carbon dioxide. Additional data have also revealed the presence of nickel and cyanogen, neither of which are known to emit a green fluorescence.
The absence of C2 raises questions about the comet’s unique chemistry. According to a preprint study led by Luis Salazar Manzano from the University of Michigan, Ann Arbor, the early detection of cyanogen suggests that 3I/ATLAS is significantly depleted in carbon-chain molecules, including both C2 and C3. The researchers have stated, “Our upper limit on the C2-to-CN ratio places 3I/ATLAS among the most carbon-chain depleted comets known.”
The peculiarities of 3I/ATLAS present a fascinating mystery for astronomers. As it continues its journey through the Solar System, scientists hope to gather more data, especially when the comet makes its closest approach to Earth in December. The quest to unlock the secrets of this interstellar visitor emphasizes the ongoing exploration of celestial phenomena and their implications for our understanding of the cosmos.
As observations and research continue, the scientific community remains engaged, eager to unravel the complexities of 3I/ATLAS. With each new finding, the comet’s enigmatic nature only deepens, promising further revelations in the near future.
