A mysterious visitor from deep space is hurtling through our solar system and it’s turning out to be much larger and more puzzling than anyone expected. The object, known as 3I/ATLAS, is only the third interstellar object ever discovered, after the famous ‘Oumuamua in 2017 and 2I/Borisov in 2019. But unlike those earlier discoveries, this cosmic traveler could be far more massive, raising new questions about what it really is and where it came from.
A Rare Visitor From Beyond Our Solar System
For the past two months, astronomers have been tracking 3I/ATLAS as it speeds through the solar system. It’s traveling so fast that it’s clear it came from outside our solar system, making it a rare and valuable object for scientists to study. Early observations suggested that it was a comet a frozen body made mostly of ice and dust but new research is challenging that view.
One of the most surprising findings is that 3I/ATLAS contains far more carbon dioxide (CO₂) than scientists expected. This unusual composition already sets it apart from most known comets. But the mystery deepened even further when Harvard astrophysicist Avi Loeb and his team analyzed its motion in space.
Far More Massive Than Expected
Loeb, known for his bold ideas about interstellar objects, studied the object’s non-gravitational acceleration small changes in its speed and direction caused by gases and dust escaping from its surface. Based on this data, Loeb concluded that 3I/ATLAS must weigh more than 33 billion tons. That means its solid nucleus could be over 3.1 miles (5 kilometers) wide, putting it at the upper end of all current size estimates.
If Loeb’s calculations are correct, that would make 3I/ATLAS three to five orders of magnitude more massive than ‘Oumuamua or Borisov. For comparison, ‘Oumuamua was only about 0.25 miles long, while Borisov measured about 0.6 miles. A nucleus over 3 miles wide would make 3I/ATLAS truly gigantic.
A Strange and Unusual Trajectory
The object’s path through the solar system is another reason scientists are intrigued. Its trajectory will take it suspiciously close to several planets, including Jupiter, Venus, and Mars. In just over a week, it will pass within 1.67 million miles of Mars’ orbit a remarkably close encounter on a cosmic scale.
Loeb calls this “remarkable fine-tuning,” suggesting the path is unusual enough to raise questions about its origin. With so few interstellar objects ever detected, the odds of finding one this large and this close to Mars seem extremely low.
Alien Artifact or Natural Wonder?
Loeb is not ruling out a controversial possibility: that 3I/ATLAS might not be a natural object at all. He has previously suggested that interstellar objects like ‘Oumuamua could be artifacts of advanced extraterrestrial technology. In this case, if the object’s core turns out to be larger than 3.1 miles, Loeb argues that it may not fit with known models of natural interstellar material formation.
“Is 3I/ATLAS an unusually massive comet with an unusual chemical composition on an unusually rare trajectory or alien technology?” Loeb asked in a recent blog post. “In both cases, the object could shed CO₂ and H₂O ices from material that collected on its frozen surface as it traveled through interstellar space.”
A Rare Opportunity for Closer Study
The upcoming close approach to Mars provides a rare opportunity to study 3I/ATLAS in detail. Loeb and other scientists are urging NASA to point the HiRISE camera on the Mars Reconnaissance Orbiter at the object during its pass. A high-resolution image could reveal its true size, surface composition, and reflectivity, helping astronomers determine whether it’s a natural comet or something far stranger.
The brightness of the object’s reflected sunlight will give scientists key clues about its size and surface properties. This data could confirm or challenge current theories about what 3I/ATLAS really is.
The Mystery Continues
Whether 3I/ATLAS is an unusually massive comet, a cosmic oddity, or even a piece of alien technology, one thing is certain: it’s one of the most intriguing interstellar visitors we’ve ever seen. As it races toward Mars, scientists around the world are watching closely, hoping to unlock the secrets of this enormous and mysterious object.
Whatever the final answer turns out to be, 3I/ATLAS is a powerful reminder of how much we still have to learn about the universe beyond our solar system and how many surprises could still be on their way.
Source: Futurism, Yahoo News, Avi Loeb Blog (September 25, 2025)