3I/ATLAS Is Leaving the Solar System Forever — Here's How to Watch It Go

Comet 3I/ATLAS, the third confirmed interstellar object to enter our solar system, is now racing into the cosmic dark on a hyperbolic trajectory that ensures it will never return.

First detected in July 2025, the alien visitor has captivated astronomers with its unpredictable light changes, rare composition, and unbound orbit.

As it departs, skywatchers across the Northern Hemisphere have one last opportunity to witness its farewell in the pre-dawn sky through mid-December.

A Visitor From Beyond the Solar System

Unlike typical comets that orbit the Sun, 3I/ATLAS originated from outside our solar system. Its hyperbolic path confirms it is not gravitationally bound to the Sun and will eventually escape into deep space. NASA has verified its status as an interstellar object, joining 1I/ʻOumuamua and 2I/Borisov as rare cosmic interlopers.

According to NASA, the comet made its closest solar approach (perihelion) on 29 October 2025, passing about 1.4 astronomical units from the Sun — roughly 130 million miles. During this period, observatories worldwide tracked its speed, estimated at over 100,000 mph, to study its dust composition and glean clues about its origin from other star systems.

Final Journey Out of the Solar System

Comet 3I/ATLAS is expected to leave our solar system permanently around January 2026. The interstellar visitor passed its perihelion, or closest approach to the Sun, in late October 2025 at approximately 1.4 astronomical units from the Sun.

Following this, it is moving away on a hyperbolic trajectory, meaning it is not gravitationally bound to return to our solar system. Astronomers have calculated its path with precision, allowing scientists and space enthusiasts to track its journey in real time until it disappears from view.

How and When To See 3I/ATLAS Before It Vanishes

Following its solar flyby, 3I/ATLAS is now reappearing in the night sky, becoming visible again to observers in the Northern Hemisphere. The comet will be at its brightest in mid-November and will likely remain visible until early December. It will appear in the eastern pre-dawn sky, gradually shifting northward.

To view the comet:

• Best time: Best viewed during pre-dawn hours.
• Direction: Look east-northeast, low on the horizon.
• Equipment: A telescope or high-powered binoculars is recommended, at least 8 inches (20 cm) in diameter, as the comet's brightness may not be sufficient for the naked eye.

The Science Behind Its Changing Colours

Astronomers have noted unusual colour changes in 3I/ATLAS, from greenish hues typical of carbon-rich comets to a bluish glow following its solar flyby.

Researchers suggest that these shifts could indicate the presence of volatile gases and complex hydrocarbons, which are unique to materials formed outside our solar neighbourhood.

Data from the European Space Agency (ESA) indicate that the comet's coma has been emitting light at wavelengths not commonly seen in known comets — a clue that it may contain exotic ices or molecular compounds from a distant stellar nursery.

Farewell To A Cosmic Wanderer

By January 2026, 3I/ATLAS will have fully exited the solar system, never to return. Its journey, spanning millions of years across interstellar space, offers scientists an unprecedented opportunity to study planetary formation processes beyond our Sun.

As it fades into the void, 3I/ATLAS reminds observers of the vastness of our universe and the fleeting nature of such encounters.

For many astronomers, it is not just a scientific event but a moment of cosmic reflection — a final glimpse of a traveller from the stars before it becomes legend.