Why Interstellar Comet 3I/ATLAS Appears to Have “Lost” Its Tail — What Astronomers Have Discovered

Astronomers have obtained breathtaking new photographs of the interstellar comet 3I/ATLAS, a bright green object that is presently moving fast away from the Sun — but something perplexing has come up. Even though the comet looks very bright, the latest studies have indicated that the peculiar dust tail of the comet appears to be absent. The scientists, however, claim that it is not actually lost — it is simply concealed in the view.

🔭 Latest Observation From Arizona

On November 5, 2025, Qicheng Zhang, a researcher at the Lowell Observatory in Arizona, used the observatory’s Discovery Telescope to capture detailed images of 3I/ATLAS. The comet, which recently passed behind the Sun, has now re-emerged and is visible again as it journeys farther into deep space.

☄️ What Makes 3I/ATLAS Glow Green?

As usual, comet 3I/ATLAS exhibits its glowing atmosphere (coma) near the Sun. The Sun's rays heat the comet, thus vaporizing its icy surface and the gas and dust that have been released and are reflecting the sunlight. The comet looks extraordinarily bright through a green optical filter, and this is the very green color that results from its distinctive chemical composition.

As put by Zhang, large hydrocarbons within the comet get broken down by the Sun's ultraviolet (UV) rays, and the resulting molecule is diatomic carbon (C₂), which has a green light-emitting property when excited by solar radiation.

“It’s like how UV rays cause sunburns in humans,” explained Zhang. “The same UV radiation is breaking down carbon-based molecules in the comet’s surface.”

🌀 The “Missing” Tail Mystery

Images taken after 3I/ATLAS’s reappearance show no visible dust tail, leading some to speculate it had vanished. However, Zhang clarified that the tail is still there, just angled directly away from Earth — making it appear invisible from our perspective. The faint curvature of light around one side of the comet indicates that the tail is positioned almost directly behind the nucleus.

🌌 A Rare Visitor From Beyond the Solar System

Discovered in July 2025, 3I/ATLAS is only the third known interstellar object ever detected passing through our Solar System — after ʻOumuamua (1I/2017 U1) and 2I/Borisov. It is believed to have originated from a distant stellar system in the Milky Way, possibly making it billions of years older than our Sun.

The comet made its closest approach to the Sun (perihelion) on October 29, reappearing in early November — a phase when comets typically exhibit their most dynamic activity.

🧪 What Scientists Have Learned So Far

Early findings suggest that 3I/ATLAS has developed a thick, irradiated crust due to prolonged cosmic exposure. This means the comet may now be releasing altered materials, rather than pristine samples from its original system — a fascinating clue for astronomers studying interstellar chemistry.

On October 31, Zhang captured the first post-perihelion optical images of the comet at dawn as it rose above the northeastern horizon. Previous data also revealed that before perihelion, 3I/ATLAS brightened rapidly and appeared slightly blue — a color shift confirmed through filtered imaging.

🔭 Visible to Amateur Astronomers

Now positioned more favorably in the night sky, 3I/ATLAS can be spotted using moderate-sized telescopes — even amateur astronomers with instruments as small as 15 cm in diameter may observe it in coming weeks.

“It’s an exciting opportunity,” Zhang said. “We’re witnessing an interstellar visitor evolving in real time as it leaves our Solar System.”