The imminent solar conjunction of 3I/ATLAS | by Avi Loeb | October 2025

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On October 21, 2025, interstellar object 3I/ATLAS will be located exactly on the opposite side of the Sun from Earth, constituting what is called a “solar conjunction.” As you look to the sky that day, keep in mind that 3I/ATLAS is hidden behind the Sun. Under these circumstances, it is impossible to observe 3I/ATLAS with ground-based telescopes, even shortly after sunset. Was this hiding place planned as an opportune moment for technological action?

In astronautics, the optimal point for a maneuver to accelerate or slow down a spacecraft is the closest approach to a massive object. An impulse in the direction of or away from maximum velocity would maximize the gain or loss of kinetic energy. As a result of what is called Oberth effectIt is more energy efficient for a spacecraft engine to burn its fuel when its orbital speed is highest. The velocity pulse of the gas escaping from the exhaust is analogous to the so-called Hills mechanism for the production of hypervelocity stars from the tidal disruption of a binary star system by a supermassive black hole (theoretically predicted here and observationally confirmed here).

If 3I/ATLAS is a massive mothership, it will likely continue its original gravitational path and eventually leave the solar system. In this case, Oberth’s maneuver could apply to the mini-probes that it launches at perihelion towards the planets of the solar system.

When will 3I/ATLAS reach the optimal time for these Oberth maneuvers? Only 8 days after reaching solar conjunction. On October 29, 2025, 3I/ATLAS will reach a perihelion distance of 203 million kilometers. This opportune moment occurs during the same period when it is hidden from the view of terrestrial telescopes. Was this a simple coincidence or the result of orbital design and basic astronautics?

Science is driven by evidence, not expectations. We can find the answer to the question above by monitoring the sky in November and December 2025 and looking for any unusual activity from 3I/ATLAS or any new objects that have emerged from it. For several months after perihelion, the Sun’s tidal force would separate the trajectories of objects projected out of 3I/ATLAS with bursts of speed.

Given the minimum diameter of 5 kilometers for 3I/ATLAS (as derived here), perihelion solar illumination would provide more than 33 gigawatts of power on its surface, or at least a third of the total power generated by 94 operating commercial nuclear reactors in the United States – the world’s largest producer of nuclear power.

For now, 3I/ATLAS appears to be a natural comet. But the slim possibility of an Oberth maneuver should be seriously considered as a black swan event with low probability, due to its enormous implications for humanity. Since its discovery on July 1, 2025, 3I/ATLAS has been ranked 4th on the Loeb scale (quantified here and here) because of 8 anomalies:

1. The trajectory of 3I/ATLAS is aligned within 5 degrees with the plane of the ecliptic of the planets around the Sun (see here).

2. 3I/ATLAS showed a jet towards the Sun (anti-tail) which is not an optical illusion from a geometric point of view, unlike the familiar comets (see here).

3. 3I/ATLAS is about a million times more massive than 1I/`Oumuamua and a thousand times more massive than 2I/Borisov, while moving faster than both (see here and here).

4. The arrival time of 3I/ATLAS allows it to pass within a few tens of millions of kilometers of Mars, Venus and Jupiter (see here).

5. The gas plume around 3I/ATLAS contains significantly more nickel than iron (as found in industrially produced nickel alloys) and a nickel/cyanide ratio that is an order of magnitude higher than that of all known comets, including 2I/Borisov (see here).

6. The 3I/ATLAS gas plume contains only 4% water by mass, the main constituent of familiar comets (see here).

7. 3I/ATLAS showed extreme negative polarization, unprecedented for any known comet, including 2I/Borisov (see here).

8. 3I/ATLAS arrived from a direction coinciding with the radio signal “Wow! Signal” to within 9 degrees (see here).

Fortunately, we hope to obtain data from 3I/ATLAS shortly after perihelion. On November 4, 2025, ESA Explorer of Jupiter’s icy moons (Juice) will pass within a radius of 64 million kilometers from 3I/ATLAS. If 3I/ATLAS maintains a trajectory shaped solely by gravity, it will approach Earth on December 19, 2025 at a distance of 269 million kilometers. On March 16, 2026, 3I/ATLAS will pass within 54 million kilometers of Jupiter and will be observable by sensors in the UV, infrared and radio bands on board the satellite. Juno spacecraft (as recommended scientifically here and politically here).

Hopefully the coming months will provide enough information to determine the true nature of 3I/ATLAS. In a blind date of interstellar proportions, it’s best to observe the other side as much as possible before forming an opinion or raising expectations about an engagement.

ABOUT THE AUTHOR

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Avi Loeb is the leader of the Galileo Project, founding director of the Black Hole Initiative at Harvard University, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and former chair of the Department of Astronomy at Harvard University (2011-2020). He is a former member of the President’s Council of Advisors on Science and Technology and former chairman of the Council on Physics and Astronomy of the National Academies. He is the bestselling author of “Alien: The first sign of intelligent life beyond Earth» and co-author of the manual «Life in the cosmos», both published in 2021. The pocket edition of his new book, entitled “Interstellar», was published in August 2024.