Both objects share the same fundamental contradiction, which is why scientists argue they defy easy categorization as standard comets or asteroids.

The central paradox linking both objects is: Non-Gravitational Acceleration Without the Necessary Evidence of Cometary Outgassing.

1. The Core Mechanical Anomaly (The "Dark Comet")

- 1I/`Oumuamua (2017): This object was the first to be definitively proven to be pushed slightly away from the Sun by a force other than gravity. The traditional explanation for this non-gravitational acceleration is the rocket-like thrust created when volatile ices (like water or carbon dioxide) on a comet sublimate, creating a visible gas and dust tail. However, deep observations by telescopes like Spitzer found absolutely no gas or dust—no visible tail. This forced astronomers to invent the oxymoron of the "dark comet," a comet that accelerates like a comet but has no visual sign of being one.

-3I/ATLAS (2025): The new data confirms that 3I/ATLAS is also exhibiting significant non-gravitational acceleration—meaning it, too, is being pushed. The anomaly here is the same: the acceleration is so large it requires the object to have lost a massive percentage of its mass (around 13%), yet initial images taken since its pass behind the Sun show no clear, enormous cometary tail or debris cloud commensurate with that mass loss. It repeats the "dark comet" problem, but on a massive scale.

2. The Path and Probability Anomaly

1I/`Oumuamua (2017):

-This object was puzzling because its velocity relative to nearby stars was almost zero. This made its presence in our solar system at that moment extremely improbable if it were a randomly ejected object from another system.

-3I/ATLAS (2025):

This object presents its own statistical improbability: its orbit is closely aligned with the flat ecliptic plane where all our solar system's planets reside (within about $5^\circ$ tilt), which has only a $0.2\%$ chance of happening randomly.

Furthermore, its path brought it in close proximity to multiple planets (Mars, Venus, Jupiter), which is highly unlikely if its trajectory were entirely random.

The Fundamental Recursion:

In both cases, when the data (acceleration without a tail) contradicts the prevailing theory (it must be a comet), the scientific community's primary move has been to hypothesize the existence of a brand new, never-before-seen class of natural object (a nitrogen iceberg, a hydrogen comet, etc.) to close the loop.

Loeb's central argument is that the repeated occurrence of these exact same statistical and mechanical anomalies suggests the pattern is the anomaly itself, which points toward an explanation outside the standard natural lexicon.

(http://www.autoadmit.com/thread.php?thread_id=5796138&forum_id=2id.#49419606)