3I/ATLAS Still Has A High 'Loeb-Scale' Rating Of 4—What Does That Mean?

The interstellar object 3I/ATLAS has been assigned a Level 4 rating on the Loeb-Scale, a classification that signals a combination of natural anomalies and features that meet early technosignature criteria.

The unusual rating, developed by Harvard astrophysicist Professor Avi Loeb and his collaborators, positions the object in the same significance band once held by 1I/'Oumuamua.

While the broader scientific community maintains that 3I/ATLAS is most likely a natural comet, the object's behaviour continues to draw heightened scrutiny as new data arrives.

Discovered on 1 July 2025 by the ATLAS survey telescope in Chile, 3I/ATLAS (C/2025 N1) is the third confirmed interstellar object to pass through our Solar System, following 1I/'Oumuamua and 2I/Borisov.

NASA's Hubble and JWST missions have been tracking its activity since discovery, as international observers attempt to understand its highly energetic and unconventional motion.

What A Level 4 Loeb-Scale Rating Means

The Interstellar Object Significance Scale (IOSS), informally known as the Loeb Scale, extends beyond the traditional Torino Scale by assessing anomalies and potential technosignature indicators.

Levels 0–3 accommodate objects that show natural but increasingly unusual behaviour. Level 4, however, marks the threshold at which 'anomalies meet potential technosignature criteria', meaning the object displays unexplained features that warrant further observation.

For context, 2I/Borisov scored Level 0 due to its textbook cometary behaviour. 'Oumuamua reached Level 4 because of its non-gravitational acceleration and lack of a detectable coma—issues still debated today.

While Level 4 does not imply artificial origin, it indicates that the object cannot yet be fully explained by known natural mechanisms.

The Anomalies Placing 3I/ATLAS At Level 4

The Level 4 designation arises from an accumulation of persistent anomalies rather than a single irregularity:

1. Non-Gravitational Acceleration
Researchers have detected acceleration during its perihelion passage on 30 October 2025, with a measurable push away from the Sun. Some astronomers attribute this to outgassing, but the visible coma appears too weak to account for the magnitude fully.

2. Atypical Chemical Signature
Spectroscopic observations revealed a vapour dominated by nickel with unusually low iron content. This nickel-rich composition is unlike those of thousands of catalogued comets. While hypotheses speculate about the origins of industrial alloys, mainstream scientists caution that exotic cometary origins remain plausible.

3. Rare Trajectory Alignment
Despite its hyperbolic path (eccentricity ≈ 6.15), the object travels retrograde yet aligns within roughly five degrees of the ecliptic. Such alignment, though possible, is statistically uncommon for interstellar debris.

Natural Explanations Still Favoured by Most Scientists

NASA-aligned planetary scientists argue that the anomalies remain within the outer bounds of natural comet behaviour, especially given 3I/ATLAS's confirmed detection of water ice and carbon dioxide.

Its CO₂-to-water ratio—estimated around 8—is one of the highest ever measured in a comet, but not beyond physical possibility. Mainstream analysis stresses that interstellar formation environments can produce highly unusual chemical and dynamical profiles.

Nonetheless, the Level 4 rating ensures intensified monitoring. The United Nations' International Asteroid Warning Network (IAWN) has included 3I/ATLAS in an active planetary-defence exercise from 27 November 2025 through 27 January 2026. Data from this window will be pivotal in determining whether the object will be downgraded or, more controversially, upgraded on the scale.