Avi Loeb On 3I/ATLAS: 'Probably Not Tourists' With 'Ion-Thrusters'

Avi Loeb warns that 3I/ATLAS may be far more than just a comet—its survival and 'directional jets' hint at engineered ion thrusters, not tourist visitors.

A Surprising Survivor

The Harvard astrophysicist Avi Loeb, who heads the Galileo Project, argues that the interstellar object 3I/ATLAS defies natural explanations.

Writing on the platform Medium, Professor Loeb suggests that its jets behave less like cometary outgassing and more like 'technological thrusters which preserve global orientation for navigation purposes.'

Loeb highlights what he calls the '12th anomaly': although the nucleus rotates roughly every 16.16 hours, the jets remain tightly collimated over scales of a million kilometres. According to Loeb, they should be smeared or twisted, but they are not.

Integrity Where Destruction Was Expected

Loeb points to images taken by the Nordic Optical Telescope after 3I/ATLAS's close pass around the Sun. Despite intense solar heating at perihelion, the object 'continues as an active, single body, with no evidence for breakup.'

That, he says, is surprising for a body that, if icy and cometary, should have fragmented under strain. He argues that the 'surface area required to account for the mass flow in the large-scale jets ... is untenable.'

Loeb further calculated that at perihelion, the Sun would supply about 700 joules per square metre per second, which implies 3I/ATLAS would need a surface area of more than 1,600 square kilometres to drive the observed jets.

He insists that it is inconsistent with its size as estimated from Hubble observations and cannot be explained by its fragmenting into many small pieces.

The Thruster Hypothesis

To explain these anomalies, Loeb speculates that the jets may be technological thrusters, pointing their exhaust toward the Sun, which provides thrust away from it.

He suggests this could be a deliberate 'post-perihelion manoeuvre ... employed by a spacecraft that aims to gain speed rather than slow down through gravitational assist.'

If true, this would imply far more than just a cometary visitor — it might indicate intelligent design. Loeb does not claim to have proved this yet; instead, he urges more observations, especially of the mass flow and jet velocity of the object.

Sceptics Push Back

Not all scientists are convinced. Darryl Seligman, an astronomer at Michigan State University, argues that the structural integrity of 3I/ATLAS is not surprising if its nucleus is as large as some data suggest.

He estimates that even with outgassing, the spin-up time (the time it would take for its rotation speed to tear it apart) is on the order of 100 years, making disintegration during perihelion unlikely.

Moreover, other researchers note that non-gravitational acceleration (motion that can't be explained just by gravity) is common in comets, driven by recoils from outgassing.

Radio observations also complicate the picture. The MeerKAT telescope detected hydroxyl (OH) radicals, a signature of water breakdown, which strongly supports a natural cometary origin.

Why 'Probably Not Tourists' Rings True—for Now

Loeb's framing—that 3I/ATLAS might not be a passive visitor—stems from more than speculation. He is asking serious scientific questions based on quantitative anomalies.

He does not claim definitive proof of alien intelligence, but he insists that the data so far challenge standard comet models.

What's Next? Close Watching

As 3I/ATLAS continues its journey, astronomers will closely monitor its jets, mass loss, and trajectory.

Loeb believes forthcoming data could either bolster the thruster hypothesis or reinforce more conventional cometary models.

Regardless of the outcome, 3I/ATLAS remains one of the most mysterious and debated interstellar visitors in recent memory.