Today I co-authored an intriguing new paper with the brilliant collaborators Adam Hibberd and Adam Crowl from the Initiative for Interstellar Studies in London, UK. The paper is accessible here.
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.
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