Comet or alien probe? Interstellar object makes once-in-a-lifetime pass, sparks wild debate

An unusually comet has entered the Solar system.

It poses no harm to Earth, say astronomers.

That's the good news.

Then one astronomer has made an outrageous claim: It is, quite possibly, an alien probe.

Harvard expert Avi Loeb argues there’s more to it than just a celestial object or an unusual interstellar visitor.

The reason: the object is moving “unusually fast”, and “at an extremely unusual” path.

When was it discovered, who discovered it?

3I/ATLAS was discovered by NASA’s ATLAS (Asteroid Terrestrial-impact Last Alert System) telescope in Rio Hurtado, Chile, on July 1, 2025.

It was initially spotted careening toward the inner solar system from the direction of Sagittarius. 

So is 3I/ATLAS a comet?

3I/ATLAS, also known as C/2025 N1, is classified as a newly discovered “interstellar” system – meaning, it originated from outside our solar system.

It is only the third of its kind observed visiting our solar system, after 1I/ʻOumuamua (2017) and 2I/Borisov (2019).

Unlike most comets, 3I/ATLAS originated from outside our solar system. 

Strangely enough, Oumuamua was also an interstellar object which slingshotted around the Sun, sped up and deviated from its expected trajectory, and was propelled by a mysterious force on its way out of the Solar System.

This contradicts established knowledge about comets. Scientists were left with four months' worth of data with clashing observations sa they tried to make sense of it. This led to a range of theories.

This, most astronomers tracking 3I/ATLAS speculate that it likely ejected from another star billions of years ago. Most agree it's likely a comet.

Proof of alien life?

However, one man — Harvard University astrophysicist Avi Loeb —  says it may be proof of alien life.

“The unusual trajectory of this object opens the possibility that it might have been designed to have some goals as a reconnaisance mission,” he said, referring to 3I/ATLAS. 

The mission may have been sent from an alien civilisation, he said, adding that it’s “arrogant” for human beings to think we’re all alone.

“We are a relatively young technological civilisation. And one can imagine a more advanced civilisation having an agenda, some goals, that are long term in interstellar space. Therefore, we might find probes that are still functional, and are entering the solar system with a purpose."

Mainstream astronomers are still gathering data on the I3/ATLAS offers, which they said could offer a rare glimpse at ancient material from another planetary system.

Provocative idea

Not so Prof. Loeb, who is known for his provocative theories on interstellar visitors.

He is once again making headlines — this time over his theory stated in a scientific paper claiming that 3I/ATLAS, only the third of its kind ever observed.

Loeb has raised eyebrows with an outrageous claim: this may not be just another comet or rock from deep space — it could be an alien probe.

His suspicion hinges on two key observations: speed and trajectory.

According to Loeb, 3I/ATLAS is moving “unusually fast,” even for an object entering the solar system from interstellar space. 

More importantly, its path is “extremely unusual” — so much so that it doesn’t quite match the behaviour expected from a random ejection from another star system. 

Unexplainable behaviour

“Nature doesn’t throw objects around like this often,” Loeb said in a recent statement. “When something behaves in an unexplainable way, it’s our responsibility to consider all possibilities — even ones that might sound outrageous.”

This isn’t Loeb’s first interstellar controversy. 

In 2017, he famously proposed that 1I/ʻOumuamua, the first known interstellar object, was possibly artificial — a discarded piece of alien technology, like a solar sail or probe. 

‘Extraterrestrial’

His hypothesis, detailed in his book “Extraterrestrial”, sparked intense debate among astronomers. 

Many dismissed the idea as speculative, but Loeb maintains that “extraordinary anomalies require extraordinary explanations.”

Now, with 3I/ATLAS, he sees a familiar pattern.

While most scientists currently categorise 3I/ATLAS as a likely comet, Loeb argues that such assumptions may lead us to overlook important clues. 

To be clear, Loeb isn’t saying aliens definitely sent it. 

But he insists that the scientific method demands we investigate without prejudice, especially when something doesn’t fit existing models. 

“If we keep dismissing the possibility of non-natural origin simply because it’s ‘too wild,’ we risk missing out on the truth,” he argues.

What’s next?

Loeb is currently pushing for targeted observations using high-resolution telescopes and spectrometry to analyze 3I/ATLAS's composition and motion in greater detail. 

He also advocates for future space missions designed to intercept or observe interstellar objects more closely.

For now, most in the astrophysics community remain cautious — waiting for more data and resisting speculation. 

But as with ʻOumuamua, Loeb’s theory ensures one thing: the conversation about extraterrestrial life is far from over.