When the interstellar visitor 3I/ATLAS got closest to Earth on December 19, it left more than just a green glow behind. It left behind a lot of questions that sound like the plot of a sci-fi movie. While most of us were getting ready for the holidays, Harvard astrophysicist Avi Loeb was thinking about a much darker possibility: could this cosmic guest be raining down poisonous debris on our planet as it passes by?
The ATLAS survey telescope in Chile found the object on July 1, 2025, and since then, scientists have been very interested in it because of its strange behaviour and unusual chemical makeup. Loeb, a scientist who is never afraid to look into the strange, recently asked if any of the material left behind by the visitor—the third interstellar object ever found after 'Oumuamua and Borisov—could actually reach our atmosphere.
The Toxic Plume of 3I/ATLAS
The concern stems from the massive gas plume surrounding the object. Observations have confirmed that this shroud contains cyanide and hydrogen cyanide—substances that are famously lethal. In fact, hydrogen cyanide was utilised as a chemical weapon during the First World War, a fact Loeb pointed out when discussing the potential toxicity of the comet's tail. Loeb's comparison to a 'cyanide tablet' highlights the extreme concentration of these gases, which are significantly higher than those typically seen in comets originating from our own solar system.
Data from the Atacama Large Millimeter/Submillimeter Array (ALMA) in Chile previously detected significant amounts of methanol and hydrogen cyanide within the body during the autumn months. This led to the provocative suggestion that 3I/ATLAS might be acting like a 'serial killer' of the cosmos, spreading poison through the galaxy like a giant, interstellar cyanide tablet. Scientists were particularly surprised by the sheer scale of the object's nucleus, which is estimated to be up to 46 kilometres (28 miles) in diameter—making it millions of times more massive than 2I/Borisov.
However, before we start reaching for gas masks, the physics of our solar system provides a natural shield. Loeb's latest analysis suggests that the solar wind acts as a celestial broom. Based on mass loss rates measured by the James Webb Space Telescope—which recorded the comet shedding carbon dioxide at a rate of 129 kilograms per second—any gas shed by the object would likely be swept away at a distance of just a few million kilometres from the body itself. Considering 3I/ATLAS was roughly 170 million miles away at its closest point, the 'poison' is unlikely to ever touch our air.
Tracking the Artificial Origins of 3I/ATLAS
Beyond the chemical scares, the physical debris poses another question. Loeb theorised that tiny dust particles, smaller than a micrometre, are pushed away by solar radiation pressure. Larger chunks of rock, provided they are less than three feet in diameter, would simply burn up as harmless meteors if they ever reached Earth.
'Given the mass loss rate of 3I/ATLAS, there are less than a million of these large objects released in recent months,' Loeb noted. He calculated that even the closest of these projectiles would never come nearer than ten times the Earth's radius. This distance is comfortably beyond the reach of our gravity, ensuring that even the largest fragments will sail harmlessly into the outer solar system.
Yet, there is a catch. Loeb, who has consistently argued that the object's unusually high eccentricity of 6.1 and its alignment with the ecliptic plane might point toward artificial origins, noted that the outcome changes if these objects are not just rocks, but 'manoeuvre by technological propulsion'. He has previously suggested that 3I/ATLAS could be an alien craft dispatching 'satellites' to Jupiter to gather intelligence.
The object is currently hurtling toward the gas giant, with an expected arrival date of 16 March 2026. It is expected to pass within approximately 33 million miles of Jupiter. Loeb believes the visitor could use its proximity to Jupiter to 'seed' the planet with additional probes for an unknown extraterrestrial civilisation. Whether it is a poisonous comet or an alien scout, 3I/ATLAS continues to ensure that our gaze remains fixed firmly on the stars.
While the scientific community remains divided on whether the object is a 'cosmic serial killer' or a high-tech scout, one thing is certain: 3I/ATLAS has fundamentally challenged our understanding of what lies in the space between stars. As it continues its journey towards the outer reaches of our solar system, the data gathered will undoubtedly fuel debates for decades to come.
