Avi Loeb has narrated this article for you to listen to.
The foundation of science is based on the humility to learn, not the arrogance of expertise. When comet experts argued that the interstellar object 3I/ATLAS must be a familiar water-rich comet as soon as it was discovered in July, they behaved like artificial intelligence systems: only able to reflect the data sets they were trained on. For decades, the data set that established comet expertise largely comprised icy rocks in the solar system. My counterpoint is simple: humanity launched technological objects into space, so we must conclude that alien life forms could do the same. This possibility must be added to the training data set of comet experts when studying interstellar objects.
To illustrate why, consider the following: on 2 January 2025, the Minor Planet Center – officiated by the International Astronomical Union to catalogue space objects – identified a ‘near-Earth asteroid’. A day later, the officials realised that this ‘asteroid’ was following the same trajectory of the Tesla Roadster launched by Elon Musk’s SpaceX in 2018. They immediately removed the object from their asteroid catalogue, realising that it was not in fact a rock but a car. Musk, statistically, is not the most accomplished space entrepreneur in the Milky Way over the past 13.8 billion years. There are about a hundred billion stars with similar properties to the sun in the Milky Way; roughly a tenth of them host a habitable Earth-size planet. If you roll the dice on billions of Earth-sun analogues, surely you would – or at least could – find other space entrepreneurs on some exoplanets? There is no reason why 3I/ATLAS is not a ship launched from one of them.
Most stars are billions of years older than the sun. Our Voyager spacecraft, with its 1970s technology, can reach the opposite side of the galaxy over the course of a billion years. This implies that there has been plenty of time for interstellar artefacts, potentially more advanced than Voyager or the Tesla Roadster, to reach our solar system from interstellar space. But would comet experts recognise these visitors as technological artefacts if their training data set includes only icy rocks? I do not believe so.
Let’s look at the evidence. I have identified eight anomalies of 3I/ATLAS:
Its trajectory opposite to the direction of motion of the planets is aligned to within five degrees with the ecliptic plane of the planets around the sun, with a likelihood of 0.2 per cent. This suggests that it may have been designed to do this.
During July and August, as well as early last month, it displayed a sunward jet (anti-tail) that is not an optical illusion from geometric perspective, unlike familiar comets. This might be a technological signature.
Its arrival time was fine-tuned to bring it within tens of millions of kilometres from Mars, Venus and Jupiter and be unobservable from Earth at perihelion (when an object is closest to the sun), with a likelihood of 0.005 per cent.
Its gas plume contains much more nickel than iron (as found in industrially produced nickel alloys) and a nickel to cyanide ratio that is orders of magnitude larger than that of all known comets, with a likelihood below 1 per cent. This may be a signature of industrial production of its surface.
Humanity launched technology into space, so we must conclude that alien life forms could do the same
Its gas plume contains only 4 per cent water by mass, a primary constituent of familiar comets.
It exhibits jets in the direction of the sun and opposite to it, which requires an unreasonably large surface area in order to absorb enough sunlight to sublimate enough ice to feed the mass flux of these jets. Perhaps the jets originate from technological thrusters.
Near perihelion it exhibits non-gravitational acceleration which should require massive evaporation of at least 13 per cent of its mass, whereas preliminary images indicate that the object maintained its integrity and did not break up. Perhaps this acceleration was produced by an engine.
Its tightly collimated jets maintain orientation across a million kilometres in multiple directions relative to the sun. This might imply that they are used for navigation or associated with the release of mini probes from a mothership.
If 3I/ATLAS is technological, it could pose a threat to humanity. We do not have a response protocol for alien technology, but after the first encounter – as long as we survive it – there will be political will to invest trillions of dollars in a warning system of interceptors that take close-up photos of anomalous interstellar objects. 3I/ATLAS is expected to arrive closest to Earth on 19 December. Let us hope that we will not get unwanted gifts for the holidays.
In ignoring these anomalies, comet experts miss two important opportunities.
First, science needs to be viewed as a continuous process rather than as a finished product. Collecting evidence is a learning experience akin to the work of a detective. It sometimes unravels a sobering truth that was not anticipated, since nature is more imaginative than we are. This was certainly the case when quantum mechanics was discovered a century ago and revealed a physical reality that was counterintuitive to Albert Einstein’s findings.
Despite lessons from history, present-day scientists minimise the risk to their reputation by not sharing error-corrections from data and conversing with the public only once they know the final answer. In this risk-averse intellectual climate, they inform the public of their final findings in press conferences, where they behave like lecturers in the classroom. The audience is made aware of what it needs to know. By minimising the risk to their reputation, scientists promote the impression that science is an occupation of the intellectual elite.
The truth is that the mainstream of science is routinely wrong. Einstein argued between 1935 and 1940 that black holes or gravitational waves do not exist. The popular idea of supersymmetry was ruled out by Cern’s Large Hadron Collider. In addition, after four decades of occupying centre stage in mainstream theoretical physics, string theory is no closer to making unique predictions that can be tested experimentally.
Science is a work in progress. Anomalies offer a multitude of interpretations that are tested by new data that can rule out all but one of them.
Second, the mainstream defined the search for microbes as the highest priority in the 2020 US Decadal Survey of Astronomy and Astrophysics, converging on the allocation of more than $10 billion to the Habitable World Observatory and sidelining the search for technological signatures. Even if microbes are far more abundant on exo-planets, it might be easier to identify technological signatures. It therefore makes most sense to hedge our bets and invest billions of dollars in the simultaneous search for both technological and primitive life forms.
The public is much more passionate about the search for aliens than the search for microbes. Taxpayers fund science and scientists should not sideline the public’s interest when defining research priorities. I receive hundreds of emails from fans every day and many parents write that their children wish to become scientists after seeing me speak in podcasts or on television.
Remarkably, interstellar objects offer a new opportunity for both the search for primitive and technological lifeforms. We can land on an interstellar rock and return a sample of it to Earth. The returned sample may reveal the building blocks of life from another star. But if the interstellar object happens to be a technological artefact, our learning opportunities would be far greater. The fundamental question after landing on a spacecraft with buttons on its surface would be whether to press any of them.
Avi Loeb is director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics.
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