Stunning new images reveal interstellar Comet 3I/ATLAS’s green glow and growing tail

The Developing Tail of Comet 3I/ATLAS (Image: International Gemini Observatory/NOIRLab/NSF/AURA/Shadow the Scientist)

Astronomers closely monitoring comet 3I/ATLAS as it makes its way towards the Sun. The latest images reveal its growing tail. These snapshots were captured by the Gemini South telescope. What makes this comet different from others we know?

How Is Comet 3I/ATLAS Unique?

Comet 3I/ATLAS is an interstellar visitor, unlike others in our Solar System. It follows a path that takes it back to space. Scientists expect its closest approach to the Sun, or perihelion, on 29 October 2025. The comet’s tail emerges as it nears the Sun. Its tail is created by ice sublimating into gas and dust. It was actively degassing for an unusually long distance past Jupiter's orbit. This is caused by high carbon dioxide content. Carbon dioxide sublimates at lower temperatures than water ice. These features set 3I/ATLAS apart from other comets.

What Did Scientists Discover About the Comet?

The primary goal was to study the comet’s colour. Colours provide clues about dust particle sizes and composition. Spectra were also taken to analyse its chemical makeup. Karen Meech from the University of Hawai'i led the study. She says the tail’s growth indicates changing particle structure. Observations show the comet’s chemistry for the first time. The comet’s tail now clearly grows with each observation.

Gemini South used various colour filters to photograph the comet, keeping it centred in its field of view. Background stars appear as coloured streaks, moving relative to the comet. (Image: International Gemini Observatory/NOIRLab/NSF/AURA/Shadow the Scientist)

Why Is This Discovery Important?

Comets typically have two tails: one of gas and one of dust. 3I/ATLAS will pass just within Mars’s orbit. It will not cross Earth’s path. Earth’s closest encounter happens after the perihelion. Scientists expect more discoveries as the comet moves forward. The ongoing study helps reveal interstellar object mysteries. Meech describes this as a scientific milestone and wonder. She reminds us our Solar System is part of a vast galaxy. Even brief visitors such as 3I/ATLAS leave behind a lasting legacy.