As the winter solstice approached, the night sky held a secret far more intriguing than any festive light display. While most of Britain was hunkered down for the December chill, a silent, interstellar trespasser was making its closest pass to Earth. 3I/ATLAS—officially designated C/2025 N1—was discovered on 1 July 2025 by astronomer Larry Denneau using the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS) in Río Hurtado, Chile. The third confirmed visitor from the depths of interstellar space, it has spent the tail end of 2025 challenging everything astronomers thought they knew about wandering cosmic bodies.
Fresh research has now pulled back the curtain on this visitor's most bizarre feature: a 'sun-facing' tail that appears to be throwing a cosmic tantrum. While typical comets sport tails that stream away from the Sun like windblown hair, 3I/ATLAS boasts a rare 'anti-tail' that points directly at our star. Even more baffling, this structure—stretching an incredible 620,000 miles (one million kilometres) into the void—was observed 'wobbling' with mechanical precision every 7 hours and 45 minutes as it made its approach.
The Mystery Of The Sunward Jets On 3I/ATLAS
This peculiar 'anti-tail' isn't just a visual oddity; it is a fountain of outgassing material that has never been seen before on an interstellar object. Typically, solar radiation pressure and solar winds push dust and gas behind a comet. However, as 3I/ATLAS neared its perihelion—its closest point to the Sun—on 29 October 2025, it defied these expectations. At this point, the comet was traveling at a staggering 152,000 miles per hour (68 kilometres per second) and passed at a distance of 130 million miles (210 million kilometres) from the Sun.
A team of researchers, using the Two-meter Twin Telescope (TTT) in Tenerife, monitored the comet across 37 nights. They discovered that the jet structure within the coma wasn't just active—it was pulsating. This 'wobble' suggests that the icy heart of the comet is spinning like a celestial top, completing a full rotation every 15 hours and 30 minutes.
Observations from the Hubble Space Telescope have estimated the nucleus to be between 440 metres and 5.6 kilometres in diameter, moving on a record-breaking hyperbolic trajectory with an eccentricity of 6.14—the highest ever measured for a visitor to our system.
For scientists, this isn't just about a spinning rock. 'Characterising jets in 3I thus represents a rare opportunity to investigate the physical behaviour of a pristine body formed in another planetary system,' the researchers noted. It is a glimpse into the 'chemistry set' of another star system, delivered right to our cosmic doorstep.
A Toxic Legacy: Harvard's Warning On 3I/ATLAS
While scientists are amazed by the physics of the 'anti-tail,' others have raised more worrying questions about what this interstellar traveler is really carrying. Avi Loeb, an astrophysicist at Harvard, has spoken out about the possible dangers that may be hiding in that glowing green coma.
The James Webb Space Telescope (JWST) and SPHEREx found that the comet has a lot of carbon dioxide, losing about 129 kilogrammes of it every second. The Atacama Large Millimeter/Submillimeter Array (ALMA) in Chile has seen a lot of methanol and hydrogen cyanide in the body before.
Loeb called hydrogen cyanide a 'chemical weapon' used in World War I. The fact that it was there led to the provocative idea that the comet could be acting like a 'serial killer' of the cosmos, leaving behind toxic debris as it passes. But calculations show that the solar wind protects Earth by blowing these gases away before they can reach our atmosphere.
The visitor got closest to Earth on December 19, 2025, when it passed by at a safe distance of 168 million miles (270 million kilometres). 3I/ATLAS is now speeding towards Jupiter, the gas giant, after leaving the inner solar system. It is expected to pass within 33.3 million miles (53.6 million kilometres) of Jupiter on March 16, 2026.
It will, like 'Oumuamua and 2I/Borisov before it, disappear into the darkness of the outer solar system and never come back. But its wobbling jets have shown that this strange object from another galaxy is leaving behind a lot of information that will keep people looking at the stars with a mix of awe and caution for years to come.
As 3I/ATLAS speeds towards its 2026 meeting with Jupiter, it reminds us that our solar system is not a closed bubble, but part of a much larger, and sometimes dangerous, cosmic neighbourhood. There is a lot of disagreement among the world's smartest people about whether this 'intergalactic cyanide tablet' is just a natural oddity or something more planned. One thing is certain: what we know about interstellar travellers has changed forever.
