A cosmic mytery is unfolding in real-time. 3I/ATLAS is not just a comet. For astrophysicists who have been following its nearing trajectory since 1st July 2025, it is a question mark.
A Visitor from the Interstellar Void
On July 1, 2025, the ATLAS survey telescope in Chile detected a fast-moving object on a hyperbolic trajectory – the unmistakable signature of its interstellar origin – arriving from interstellar space as it emerged from behind the Sun after perihelion, at the closest point in its orbit around our star.
Designated comet 3I/ATLAS, this is only the third confirmed interstellar object to enter our solar system, following 1I/ʻOumuamua (the first known interstellar visitor) detected in 2017 and 2I/Borisov in 2019.
Unlike its predecessors, however, 3I/ATLAS appears to be rewriting the rulebook on cometary behaviour, composition and motion.
NASA’s November 19, 2025, release of multi-mission imagery and data from NASA’s Goddard Space Flight Center ignited a scientific firestorm.
We’re excited to share these images after the delay. They remind us how much we still have to learn about interstellar visitors.
Dr. Lori Glaze, Director, NASA Planetary Science Division
The findings are not merely unusual, they are statistically improbable, bordering on the inexplicable.
From water ejection at impossible distances to non-gravitational acceleration and exotic elemental signatures, 3I/ATLAS is challenging our understanding of what comets are, and what they might not be.
The Discovery and Trajectory
Interstellar Origins
Comet 3I/ATLAS was discovered inbound from interstellar space, travelling on a hyperbolic orbit with an eccentricity greater than 1.
Orbiting Bodies
Orbiting bodies follow predictable paths governed by gravity.
Using Kepler’s Laws of Planetary Motion and Newton’s Law of Gravitation, we can calculate an object’s orbital period and itstrajectory based on its mass, the mass of the central body, and the size of its orbit.
Simply put, any two masses interact through gravity, causing them to orbit around their common centre of mass. Classic examples include planets around the Sun, moons around planets, or satellites around the Earth.
This means larger orbits take much longer to complete.
Orbits are determined by the balance between gravitational pull and inertial motion. Kepler’s laws provide the geometry and timing, while Newton’s law of gravitation provides the physical explanation and formulas for calculation.
A trajectory like this ensures it will never return, confirming its origin beyond the solar system.
Its trajectory is hyperbolic, meaning it’s not bound to the Sun. That’s how we know it came from another star system.
Dr. Davide Farnocchia, NASA JPL, Near-Earth Object Program
Its velocity and angle of approach ruled out any gravitational slingshot from within our planetary neighbourhood.
Key Dates
- July 1, 2025: Discovery by ATLAS telescope in Chile
- October 2025: Observed by Mars orbiters during its perihelion phase
- November 10, 2025: MeerKAT radio telescope detects unusual emissions
- November 19, 2025: NASA releases comprehensive imagery and data
- December 19, 2025: Closest approach to Earth (270 million km)
- March 2026: Scheduled Jupiter flyby
The Anomalies That Defy Physics
Water Ejection at 2.9 AU
Perhaps the most startling revelation is that comet 3I/ATLAS is ejecting water vapour at rates comparable to a fire hose, while still located 2.9 astronomical units (AU) from the Sun.
At this distance, solar radiation is too weak to sublimate water ice under normal conditions.
This suggests either:
- An internal heat source
- Exotic materials with lower sublimation thresholds
- Or a mechanism we do not yet understand
Nickel Without Iron
Spectroscopic data from the James Webb Space Telescope (JWST) and Hubble revealed nickel emissions, and yet no detectable iron.
This is unprecedented.
In all known comets, nickel and iron are found together in trace amounts, typically in a 1:1 ratio.
The absence of iron raises questions about:
- The object’s formation environment
- Selective outgassing or shielding
- Artificial composition?
Non-Gravitational Acceleration
3I/ATLAS is not following a purely gravitational path. Its trajectory shows non-gravitational acceleration, similar to what was observed with ʻOumuamua. However, unlike ʻOumuamua, which lacked a visible coma (i.e. a bright, diffuse, cloud-like region surrounding the nucleus), Comet 3I/ATLAS’s is visibly active.
The acceleration could be due to:
- Extreme outgassing (though the directionality is inconsistent)
- Radiation pressure (unlikely given its mass)
- Unknown propulsion mechanisms
Size and Shape: Unremarkable – or Deceptively So?
The estimated diameter of the solid nucleus of Comet 3I/ATLAS is subject to uncertainty, but the most constrained observations do provide a range of measurements. The nucleus is assumed to be roughly spherical.
Observations from NASA’s Hubble Space Telescope (HST) have provided the tightest estimates for the size of the comet’s solid, icy nucleus:
- The upper limit on the diameter is 5.6 kilometres (or 3.5 miles).
- The lower limit is approximately 440 metres (1,400 feet) to 320 metres (1,000 feet), depending on the specific observation date and source.
So, initial estimates based on the reflected sunlight and thermal emissions suggest that 3I/ATLAS is estimated to be between 320 metres and 5,600 metres, placing it in the same size class as many solar system comets. This makes it larger than ʻOumuamua (estimated at 100–200 meters), but smaller than 2I/Borisov (about 1 km).
On the surface, its size appears unremarkable.
However, what makes 3I/ATLAS exceptional is not its dimensions but the disproportionate scale of its activity—its water ejection rates, compositional anomalies, and non-gravitational acceleration are orders of magnitude more extreme than what would be expected from an object of this size.
This mismatch between physical scale and energetic behaviour is one of the many reasons scientists are struggling to categorize it.
The Avi Loeb Hypothesis: 12 Anomalies
Harvard astrophysicist Avi Loeb, known for his controversial stance on ʻOumuamua, has catalogued 12 distinct anomalies in Comet 3I/ATLAS.
These include:
- Water ejection at extreme distances
- Nickel-only emissions
- Non-gravitational acceleration
- Unusual reflectivity
- Thermal inertia inconsistent with natural bodies
- Fragmentation patterns that defy tidal stress models
- Lack of rotational tumbling
- Radio emissions detected by MeerKAT
- Absence of iron
- Stable trajectory despite outgassing
- No dust tail despite high activity
- Spectral features inconsistent with known comet families
Loeb argues that the statistical unlikelihood of all these anomalies coexisting in a single natural object means that an engineered origin cannot be ruled out.
Loeb emphasizes the importance of keeping an open mind about unusual interstellar phenomena, echoing his earlier arguments about ʻOumuamua. His commentary on the NASA’s latest images release of 3I/ATLAS continues to challenge conventional interpretations, suggesting that anomalies in such objects could point to non-natural origins.
The foundation of science is the humility to learn, not the arrogance of expertise.
Prof. Avi Loeb, Harvard University
Professor Loeb made this remark while expressing frustration that NASA officials were too quick to classify 3I‑ATLAS as a conventional comet. His point was that science should remain open to unexpected data rather than rely solely on authority or consensus.
Comparative Analysis
ʻOumuamua (1I/2017 U1)
- Shape: Highly elongated, possibly pancake-like
- Activity: No visible coma or tail
- Acceleration: Non-gravitational, unexplained
- Hypotheses: Hydrogen ice, nitrogen iceberg, light sail
ʻOumuamua’s lack of outgassing made its acceleration even more puzzling. By contrast, 3I/ATLAS is visibly active, but the direction and magnitude of its acceleration still defy conventional models.
2I/Borisov
- Appearance: Classic comet with coma and tail
- Composition: Similar to solar system comets
- Behaviour: Gravitationally consistent
2I/Borisov was the most “normal” of the interstellar visitors. It behaved like a typical long-period comet, albeit with a slightly different chemical fingerprint.
Typical Solar System Comets
- Water sublimation begins around 2.5 AU
- Nickel and iron appear together
- Acceleration is gravitational unless perturbed by jets
- Coma and tail are correlated with solar proximity
Comet 3I/ATLAS violates nearly every one of these accepted norms.
Multi-Mission Observations
NASA’s November 2025 release includes data from:
- Hubble Space Telescope: High-resolution imaging of the coma
- James Webb Space Telescope: Infrared spectroscopy revealing nickel emissions
- Mars Reconnaissance Orbiter: Captured perihelion activity from Mars orbit
- MeerKAT Radio Telescope: Detected structured radio emissions on November 10
- Ground-based telescopes: ATLAS, Gemini, and others provided continuous tracking
This is the first time an interstellar object has been observed simultaneously by such a diverse array of observational instruments.
Theories and Interpretations
Natural Explanations
Some scientists argue that Comet 3I/ATLAS is simply an extreme outlier: a comet formed in a radically different environment from the comets that have been studied so far, perhaps near a red dwarf or in a metal-rich disk.
The images show a diffuse coma and faint tail, consistent with cometary activity. It looks and behaves like a comet.
Dr. Heidi Hammel, Planetary Scientist, NASA Collaborator
Others suggest:
- Crystalline water ice with embedded volatiles
- Nickel-rich core exposed by fragmentation
- Jetting from localized vents causing erratic motion
Artificial Hypotheses
Loeb and others propose that 3I/ATLAS could be:
- A fragment of alien technology
- A probe using sublimation as propulsion
- A derelict interstellar sail with residual activity
While speculative, these ideas are gaining traction due to the sheer number of anomalies.
The Road Ahead
December 19, 2025: Earth Flyby
On December 19, 3I/ATLAS will pass within 270 million kilometres of Earth. Close enough for radar imaging and high-resolution spectroscopy, this will be the best opportunity to gather data before it exits the inner solar system.
March 2026: Jupiter Encounter
Its trajectory will take it near Jupiter, offering a chance to observe gravitational interactions and potential trajectory shifts. Instruments aboard Juno and JUICE are already preparing for coordinated observations.
The Bigger Questions
Comet 3I/ATLAS forces us to confront profound questions:
- How common are interstellar visitors?
- What formation environments produce such anomalies?
- Could some of these objects be artificial?
- Are we witnessing relics of alien civilizations – or just nature’s extremes?
The answers may redefine our understanding of planetary systems, cometary physics, and even the Fermi Paradox.
When The Universe Asks Questions
Comet 3I/ATLAS is not just an astronomical curiosity. It is a cosmic enigma. Its behaviour, composition and motion defy the statistical norms of cometary science.
Whether it is a natural relic from a distant star system or something more deliberate, it demands our attention.
As the object races past Earth and toward Jupiter, scientists around the world are watching, measuring and debating.
Because sometimes, the universe does not just send us celestial objects to observe. It sends us questions that may force us to reconsider everything we thought we knew.