Interstellar Comet 3I Atlas Turns Green as It Races Through the Solar System

The vastness of space rarely offers direct evidence of material from other star systems, but the arrival of interstellar comet 3I Atlas has done exactly that. This rare visitor, only the third confirmed interstellar object ever observed, is currently passing through our solar system at immense speed and has recently undergone a striking transformation—shifting from red to a vivid green glow. Astronomers are closely monitoring this fleeting event, as it provides a unique opportunity to study ancient material formed far beyond our cosmic neighbourhood.

Discovery and Trajectory of Interstellar Comet 3I Atlas

Interstellar comet 3I Atlas was discovered in late June and quickly identified as an interstellar object due to its hyperbolic, U-shaped trajectory. This path confirms that it is not gravitationally bound to the Sun and is merely passing through the solar system.

The comet is travelling at an estimated speed of 210,000 kilometres per hour (130,000 mph). After a brief visit, it will continue back into interstellar space, never to return.

Why Interstellar Comet 3I Atlas Is Turning Green

Recent observations from the Gemini North telescope on Nov. 26 revealed that interstellar comet 3I Atlas has developed a bright coma emitting a faint green glow. Earlier observations from the Gemini South telescope in late August showed the object appeared much redder, making the colour shift especially notable.

The green colour is caused by diatomic carbon (C2), a molecule released as the comet’s icy core sublimates under increasing solar heat. When exposed to sunlight, this gas emits green light, creating the characteristic glow seen in many comets.

What the Colour Change Reveals About Its Composition

The appearance of C2 indicates that interstellar comet 3I Atlas has warmed enough to release more complex carbon-based molecules. Scientists note that sunlight rapidly breaks down these molecules, which is why the green glow remains confined to the comet’s coma and does not extend into its tail.

The shift from red to green suggests that deeper layers of the comet are now becoming active as it approaches the Sun, offering insights into its internal makeup.

Final Approach and Scientific Significance

Interstellar comet 3I Atlas is believed to be the largest and possibly the oldest interstellar object observed so far. If it originated from the Milky Way’s thick disc, it could be up to seven billion years old—older than the solar system itself.

The comet will make its closest approach to Earth on Dec. 19, passing at a distance of about 270 million kilometres (170 million miles). Astronomers are watching for a potential delayed outburst, as heat penetrating its interior could trigger the release of additional material, briefly increasing its brightness.

Interstellar comet 3I Atlas offers a rare glimpse into material formed beyond our solar system. Its rapid passage, changing colour, and possible ancient origin make it an extraordinary object of study. As it nears its closest approach and then departs forever, interstellar comet 3I Atlas continues to provide invaluable clues about the chemistry and history of other star systems.

Thought you’d like to know

What is interstellar comet 3I Atlas?
Interstellar comet 3I Atlas is the third confirmed object known to originate from outside our solar system. It follows a hyperbolic path, indicating it is not bound to the Sun. Scientists are studying it to understand material from other star systems.

Why is interstellar comet 3I Atlas turning green?
The green colour comes from diatomic carbon (C2) released as the comet heats up near the Sun. Solar radiation excites this gas, causing it to glow green. This process is common in comets but significant for an interstellar object.

How fast is interstellar comet 3I Atlas travelling?
Interstellar comet 3I Atlas is moving at about 210,000 kilometres per hour (130,000 mph). This extreme speed helps confirm its interstellar origin. It will exit the solar system after its brief passage.

When will interstellar comet 3I Atlas be closest to Earth?
The comet will make its closest approach to Earth on Dec. 19. It will pass at a safe distance of roughly 270 million kilometres (170 million miles). Observations will continue around this period.

Why is interstellar comet 3I Atlas scientifically important?
Scientists believe it may be the oldest and largest interstellar object observed so far. Studying it allows researchers to analyse primordial material from another star system. This helps expand knowledge of the galaxy’s chemical diversity.