by Avi Loeb
July 16, 2025
from AviLoeb Website

Image credit:

Stefan Kierek
 

Today I co-authored an intriguing new paper (Is the Interstellar Object 3I/ATLAS Alien Technology?) with the brilliant collaborators Adam Hibberd and Adam Crowl from the Initiative for Interstellar Studies in London, UK.

One of the solutions to Enrico Fermi's question about extraterrestrials, "where is everybody?" is offered by the dark forest hypothesis, popularized by Cixin Liu's science fiction novel "The Dark Forest."

This hypothesis proposes that our cosmic neighborhood is dangerous, filled with intelligent civilizations that are hostile and silent to avoid detection by potential predators.

In this context, the silence in searches for radio signals by the SETI community is not caused by the lack of extraterrestrial intelligent civilizations, but is instead a consequence of them fearing mutual destruction.

Our paper explores the possibility that the recently discovered interstellar object, 3I/ATLAS, may provide evidence in support of the dark forest hypothesis.

This new interstellar interloper has displayed a number of anomalous characteristics, some of which were summarized in an essay that I wrote shortly after its discovery.

In particular:
 

1. The retrograde orbital plane (defined by the orbital angular momentum vector) of 3I/ATLAS around the Sun lies within 5 degrees of that of Earth - the so-called ecliptic plane.

    

   The likelihood for that coincidence out of all random orientations is 0.2%.
   
    

2. As I showed in a recent paper, the brightness of 3I/ATLAS implies an object that is ~20 kilometers in diameter (for a typical albedo of ~5%), too large for an interstellar asteroid.

    

   We should have detected a million objects below the ~100-meters scale of the first reported interstellar object 1I/'Oumuamua for each ~20-kilometer object.
   
    

3.  No spectral features of cometary gas are found in spectroscopic observations of 3I/ATLAS.

    

   The detected reddening of reflected sunlight could originate from the surface of the object. Related data can be found here and here.

    

   The fuzz observed around 3I/ATLAS (see images here, here and here) is inconclusive given the motion of the object and the inevitable smearing of its image over the exposure time.
   
    

4. For its orbital parameters, 3I/ATLAS is synchronized to approach unusually close to Venus (0.65au where 1au is the Earth-Sun separation), Mars (0.19au) and Jupiter (0.36au), with a cumulative probability of 0.005% relative to orbits with the same orbital parameters but a random arrival time.
   
    

5. 3I/ATLAS achieves perihelion on the opposite side of the Sun relative to Earth.

    

   This could be intentional to avoid detailed observations from Earth-based telescopes when the object is brightest or when gadgets are sent to Earth from that hidden vantage point.

    

   The retrograde trajectory at a perihelion speed of 68 kilometers per second, opposite to the direction of motion of the Earth around the Sun at 30 kilometers per second, makes the velocity difference between Earth and 3I/ATLAS 98 kilometers per second.

    

   It is therefore impractical for earthlings to land on 3I/ATLAS at closest approach by boarding chemical rockets, since our best rockets reach at most a third of that speed.
   
    

6. The optimal point for a reverse Solar Oberth maneuver to become bound to the Sun is at perihelion.

    

   In an Oberth maneuver, the thrust of a spacecraft is applied at its maximum orbital speed, namely at periapsis, so as to maximize the resulting change in kinetic energy.

    

   This applies both to accelerating to achieve Solar System escape, or alternatively to slow down from a high speed (a 'reverse Oberth maneuver') in order to break, stay bound to the Sun and potentially visit a planet like Earth.

    

   It is this optimal breaking point for 3I/ATLAS that is obscured from our view by the Sun.
   
    

7. The direction from where 3I/ATLAS is coming is oriented towards the bright Milky-Way center, where crowding by background stars made its detection difficult prior to July 2025.

    

   Figures 1 and 2 in our paper show that if astronomers were to detect 3I/ATLAS more than a year earlier, then we would have had an opportunity to launch a spacecraft that could have intercepted 3I/ATLAS along its path.

    

   By now, such an interception is not feasible with chemical rockets.
   
    

8. The velocity thrusts needed for launches of gadgets out of 3I/ATLAS to intercept Venus, Mars, or Jupiter are smaller than 5 kilometers per second, achievable by intercontinental ballistic missiles.

The near alignment of the retrograde trajectory of 3I/ATLAS with the ecliptic plane offers various benefits to an extraterrestrial intelligence, since it allows a spacecraft to access Earth with relative impunity.

The eclipse of 3I/ATLAS by the Sun at perihelion for observers at Earth, would allow a spacecraft to conduct a clandestine reverse Solar Oberth maneuver, an optimal high-thrust strategy for interstellar spacecraft to brake and stay bound to the Sun.

An optimal intercept of Earth would entail an arrival in late November or early December of 2025.

Detection of a non-gravitational acceleration could also indicate an intent to intercept Jupiter, not far off the path of 3I/ATLAS, and a strategy to rendezvous with it after perihelion.

Our paper is contingent on a remarkable but testable hypothesis that 3I/ATLAS is a functioning technological artifact, to which I and my two co-authors do not necessarily ascribe.

Yet, this hypothesis is worthy of a scientific analysis for two reasons:

1. The consequences, should the hypothesis turn out to be correct, could potentially be dire for humanity, and would possibly require defensive measures to be undertaken (though these might prove futile).
    

2. The hypothesis is an interesting exercise in its own right, and is fun to explore, irrespective of its likely validity.

Given its interstellar speed of 60 kilometers per second, 3I/ATLAS entered the outer boundary of the Solar System (at 100,000 times the Earth-Sun separation) about 8,000 years ago...!

This was roughly when human-made technologies became advanced enough to start documenting history on Earth.

If the hypothesis about a technological artifact ends up being correct, then there are two possible implications:

• first that the intentions of 3I/ATLAS are entirely benign

• second that they are malign

In the first case, humanity need not do anything but await the arrival of this interstellar messenger with open arms.

 

It is the second option which is of great concern.

Given the dramatic implications of the second possibility, we can apply the logic of Pascal's wager that suggested,

it is more rational to believe in God's existence than not.

The insight offered by the mathematician Blaise Pascal was that,

the potential benefits of believing (in our case - alerting humanity to the existential risk from 3I/ATLAS) far outweigh the potential losses (in our case - a theoretical idea that does not describe reality), while the potential losses of not believing are far greater than the potential benefits.

Our paper is largely a pedagogical exercise, with interesting realizations worthy of a record in the scientific literature.

By far, the most likely outcome will be that 3I/ATLAS is a completely natural interstellar object, probably a comet, and we await the astronomical data to support this likely origin.

Nevertheless, when viewed from an open-minded and unprejudiced perspective, our paper includes many compelling insights that could be applied to tens of interstellar objects that are expected to be detected over the next decade by the Vera C. Rubin observatory.

The existential risk from alien intelligence (external A.I.) is not discussed as often as other existential risks, like artificial intelligence (our A.I.).

In a dark forest, uncertainties about one's relative strength may argue for hiding as a survival mechanism, especially if a civilization was bruised in the past.

In addition, dominance could be time dependent as there might always be some rising young technological civilization which becomes powerful quickly - requiring reconnaissance missions on trajectories similar to that of 3I/ATLAS.

We might soon realize that the extension of natural selection to interstellar space involves survival of the fittest.

In a recent essay (Spacecraft from Interstellar Rocks?), I provided a menu of methods for distinguishing an extraterrestrial spacecraft from an interstellar rock. Here's hoping that this menu will be used by other astronomers.

Ignoring the technological option is not a sign of intelligence...