Where is 3I/ATLAS Now?
By now, 3I/ATLAS is at a distance of a billion kilometers or 6.7 times the Earth-Sun separation, well beyond Jupiter. Our interstellar visitor appears as a fading dot, similar to the way it looked when it was first spotted in telescope images nearly a year ago, except that right now it is heading away from us back to interstellar space. Given how well aligned its trajectory was with the orbital plane of Earth around the Sun, we might never witness a visitor like it in our lifetime.
The brightness of 3I/ATLAS on its way out is elevated relative to its brightness on the way in because of the excess outgassing and dust shedding that it displayed close to the Sun. So far, its fading light curve does not show any evidence for artificial (self-produced) light. We are still waiting for data from NASA’s Juno spacecraft, taken around March 16, 2026 when 3I/ATLAS came closest to Jupiter.
As we say goodbye to 3I/ATLAS on its way out of the detectability horizon of our telescopes, it is time to list all of the anomalies it displayed over the past year, grouped thematically (differently than in my past essays):
1. Isotope ratios: 3I/ATLAS displayed an exceedingly high fraction of deuterium amounting to one deuterium in 100 hydrogen atoms in water (H2O, as reported here) and one deuterium in 30 hydrogen atoms in the organic molecule of methane (CH4, as reported here). The measured abundances is up to a thousand times above the average cosmic abundance, more than an order of magnitude higher than found in water in all known comets or meteorites, and three orders of magnitude higher than found in methane on solar system planets. In addition, the 12C/13C ratios (141–191 for CO2 and 123–172 for CO) was reported to exceed typical values found in the Solar System and nearby interstellar clouds or protoplanetary disks.
Potential techno-signature: Deuterium and tritium constitute an efficient fuel for nuclear fusion. If a nuclear bomb was to explode on 3I/ATLAS, it could have triggered a chain reaction by igniting the abundant deuterium in it.
2. Mass Budget Discrepancy: The inferred nucleus diameter and number density of its parent population exceed the mass reservoir of planetary disks around old stars (as inferred here and here) by orders of magnitude. More details are available here.
Potential techno-signature: Technological probes might cluster in the habitable zone of stars with an abundance that far exceeds the average value in interstellar space. This might reflect focused interest in resources, in analogy to the clustering of bees around flowers.
3. Fined-Tuned Geometry and Timing of Trajectory:
3.1. The retrograde trajectory of 3I/ATLAS is aligned to within 5 degrees with the orbital plane of the planets around the Sun, with a probability of 0.2% (as discussed here). The Milky-Way disk is misaligned with the ecliptic plane by about 60 degrees. This suggests that the trajectory of 3I/ATLAS may have been planned.
3.2. The arrival time of 3I/ATLAS was fine-tuned to bring it to minimum distances of 29 and 54 million kilometers from Mars and Jupiter, respectively, and be unobservable from Earth at perihelion (as discussed here).
3.3. The perijove distance of 3I/ATLAS during its encounter with Jupiter on March 16, 2026 is 53.6 million kilometers, is very close to Jupiter’s Hill radius, 53.5 million kilometers (as discussed here).
Potential techno-signature: The orbital plane and arrival time were selected as part of a probing or seeding (with life or gadgets) mission, targeting the habitable zone of the solar system.
4. Abundant organic molecules: Organic molecules in gas phase, such as CH3OH, H2CO, CH4, and C2H6, were discovered after perihelion (as reported here). To survive cosmic-ray bombardment along an interstellar journey that lasted billions of years, these organic molecules must have been buried under a thick layer of material, at least 10-meters in depth. The volatility of methane (CH4) is between that of carbon dioxide (CO2) and carbon monoxide (CO), yet methane was detected in the gas plume around 3I/ATLAS only after perihelion, while CO2 and CO were detected long before perihelion. This puzzle (discussed here) suggests a strange layered composition of the nucleus or a biological origin. Methane and other organic molecules are known bio-markers.
Potential bio-signature: Does 3I/ATLAS carry life on it (as discussed here)?
5. Anti-tail: Analysis of the Hubble Space Telescope image of 3I/ATLAS from July 21, 2025 (as discussed here) suggests that the anti-tail before perihelion must have been in the form of a collimated jet towards the Sun that is about ten times longer than it is wide. This is similar to the collimation observed in post-perihelion images. The anti-tail jet extended out to several hundred thousand kilometers. No known comet exhibited a physical sunward jet of this length that is not a perspective effect. The existence of a prominent anti-tail jet towards the Sun on the way of 3I/ATLAS out of the solar system requires a similar coincidence near the opposite pole of the rotation axis (as discussed here). The fact that a collimated jet appears as the sunward anti-tail both before and after perihelion (while reversing direction at perihelion relative to the direction of motion), has a tiny probability of occurring at random, equal to the square of 0.5% or 0.000025.
Possible techno-signature: For a technological object, a beam of particles might be used to block the solar wind from impacting the nucleus surface at a relative speed of order 500 kilometers per second. In addition, the veil of dust around 3I/ATLAS is just of the right column needed to block sunlight from hitting the nucleus surface (as discussed here).
6. Symmetric Jet System: Processing of several dozens of Hubble Space Telescope Images from November 2025 to February 2026 by the Larson-Sekanina filter — which removes the circularly-symmetric glow round the nucleus, reveals a system of three mini-jets which are symmetrically separated by 120 degrees from each other (as discussed here, here and here).
Possible techno-signature: The symmetric system of 3+1 jets might be associated with technological thrusters, used for stabilizing the three-dimensional motion of 3I/ATLAS (as discussed here).
7. Rotation-axis alignment: At large distances from the Sun, the initial rotation axis of 3I/ATLAS was aligned to within 8 degrees with the sunward direction when it entered the solar system (as reported here). The probability for that is 0.5%. The observed wobble of the pre-perihelion anti-tail jet in the direction of the Sun (as reported here during July and August 2025) requires the base of the jet to be within 8 degrees from the sun-facing pole, with a probability of 0.5%. The gravitational deflection of 3I/ATLAS by 16 degrees at perihelion (as discussed here), is exactly twice the opening angle of the anti-tail before perihelion. This coincidence allows the wobbling jet around the rotation axis to generate an anti-tail in the direction of the Sun before perihelion and a counter jet on the opposite pole after perihelion, with a jet opening angle of 8 degrees on both poles.
Possible techno-signature: The sunward alignment of the rotation axis allows for a steady dayside and a steady nightside throughout the inward or outward legs of the journey, maintaining stable surface temperature and illumination on the surface of a technological object. The launch base of the post-perihelion anti-tail jet resided on the nightside of 3I/ATLAS before perihelion and the base of the pre-perihelion anti-tail jet is now on the nightside of 3I/ATLAS after perihelion. For these bases to be active only when facing the Sun, they must be well insulated on the nightside for a period longer than several months. Heat naturally flows by conduction throughout the body of a natural comet, making this insulation requirement difficult to satisfy in a natural rock.
8. Rare arrival direction: 3I/ATLAS arrived from a direction coincident with the radio “Wow! Signal” to within 9 degrees, with a probability of 0.6% (as discussed here).
Potential techno-signature: Did the radio signal originated from a companion of 3I/ATLAS or its senders?
9. Unusual chemical composition: Before perihelion, the gas plume surrounding 3I/ATLAS contained 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 for thousands of known comets, including 2I/Borisov (as reported here). After perihelion, iron was detected.
Potential techno-signature: Nickel overabundance relative to iron is a characteristic of nickel alloys which are produced industrially for aerospace applications.
10. Extreme Polarization: 3I/ATLAS showed extreme negative polarization, unprecedented for all known comets, including 2I/Borisov (as discussed here and here).
Potential techno-signature: This unusual polarization may be related to its unresolved geometry or unusual anti-tail.
11. Extreme brightening: Near perihelion, 3I/ATLAS brightened faster than any known comet and was bluer than the Sun (as discussed here).
Potential techno-signature: Does this brightening signals artificial lights or charging a technological device by sunlight?
12. Size and mass: The nucleus of 3I/ATLAS is more massive than 1I/`Oumuamua and 2I/Borisov, while moving faster than both (as discussed here and here).
Potential techno-signature: Is 3I/ATLAS a Trojan Horse, namely a natural comet that was hitchhiked by a technological civilization which used its resources to navigate it into the habitable zone of the Solar System?
Altogether, these anomalies led me to rank 3I/ATLAS as Level 4 on the Loeb Scale (as discussed here, here, here and here).
Given that 3I/ATLAS is on its way out of the Solar System, its anomalies might remain unresolved. If the DOE-NSF Rubin Observatory will detect a new object that resembles 3I/ATLAS and indicates that it may have returned, that by itself would constitute a startling technological signature. This time around, we will have to launch a mission that will intercept its path, take a close-up photograph of its nucleus and crash the interceptor with the camera on it. This will be the best way to show that we all have a crush on returning dating partners.
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, former director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics (2005–2026), and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
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