Imagine a cosmic object, hurtling through space, defying the predictable pull of gravity. This is 3I/ATLAS, an interstellar visitor, and its behavior is causing quite a stir among astronomers. But here's the really intriguing part: its unusual acceleration might just be a clue to something far more extraordinary than we ever imagined.
Let's dive into the details. Davide Farnocchia at NASA's Jet Propulsion Laboratory (JPL) diligently tracks the non-gravitational acceleration of 3I/ATLAS, posting updates on the JPL Horizons website (you can check it out yourself: https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=1004083&view=OPC). This "non-gravitational acceleration" refers to any force acting on the object besides the usual gravitational pull of the Sun and other celestial bodies. For comets, this is often due to the sublimation (think of it as "evaporation" for solids) of ice as they get closer to the Sun, releasing gases that act like tiny rocket engines.
Initially, on October 30, 2025, the radial acceleration component, denoted as A1 and normalized to the Earth-Sun distance (1 astronomical unit, or au), was estimated at 1.6 x 10^-6 au per day squared. This tells us how much the object's speed is changing along a line pointing directly away from the Sun. However, by November 24, this value had been significantly reduced – a fourfold decrease to 4 x 10^-7 au per day squared.
Now, this is where it gets interesting. I (Avi Loeb) noticed something peculiar: the predicted closest approach (perijove) of 3I/ATLAS to Jupiter on March 16, 2026, was remarkably close to Jupiter's Hill radius. The forecast was 53.445 million kilometers, with a margin of error of just 0.06 million kilometers. Jupiter’s Hill radius, at that time, was calculated to be 53.502 million kilometers. The Hill radius represents the region around a planet where its gravity dominates over the Sun's tidal forces. Think of it as Jupiter's gravitational "sphere of influence." Any small object orbiting Jupiter outside this sphere is likely to be pulled away by the Sun.
The proximity of 3I/ATLAS's predicted perijove to Jupiter's Hill radius struck me as an unlikely coincidence. I shared my observations with Davide Farnocchia, but I didn't receive a response. But here's where it gets controversial... Within days, the A1 value on the JPL Horizons website was revised downward again, this time by a factor of six, to 6.8 x 10^-8 au per day squared. Furthermore, a new model was introduced to describe how the non-gravitational acceleration changes with distance from the Sun. The new model assumed an inverse square relationship (1/r²), which is typical for the sublimation of carbon dioxide (CO2) ice at distances closer than 5 au to the Sun. This replaced the previous model, which had a steeper radial dependence more appropriate for water (H2O) ice sublimation, based on research by Brian Marsden and his colleagues (see https://articles.adsabs.harvard.edu/pdf/1973AJ.....78..211M and https://iopscience.org/article/10.3847/1538-3881/153/2/80/pdf for details).
As a result of these revisions, the new JPL Horizons forecast places the perijove distance of 3I/ATLAS at 53.587 million kilometers (with an uncertainty of 0.045 million kilometers), placing it just outside Jupiter's Hill radius on March 16, 2026. However, and this is the part most people miss, this forecast relies on the 1/r² model, which uses past contributions from larger heliocentric distances to explain the observed deviation of 3I/ATLAS from its expected gravitational path.
I believe the new JPL Horizons model might be inadequate. There's compelling evidence suggesting that 3I/ATLAS brightened more significantly near its closest approach to the Sun (perihelion) than the smooth 1/r² model would predict. If we correct the radial dependence of the non-gravitational acceleration to account for this, it's likely to bring the predicted perijove distance back into closer agreement with the Hill radius value.
The luminosity (brightness) of 3I/ATLAS, as observed by the Hubble Space Telescope on July 21, 2025 (reported in https://iopscience.org/article/10.3847/2041-8213/adf8d8/pdf), supports a steeper radial profile. The luminosity is largely determined by the coma (the cloud of gas and dust surrounding the object), which reflects the mass loss due to sublimation. Recent research by Marshall Eubanks and collaborators (https://arxiv.org/pdf/2511.20810) and earlier work by Qicheng Zhang and Karl Battams (https://arxiv.org/pdf/2510.25035) suggest a steep luminosity profile of 1/r^{7.5} inside 2 au as 3I/ATLAS approached its perihelion distance of 1.36 au on October 29, 2025. Adopting this steeper radial dependence would likely shift the predicted perijove distance closer to Jupiter's Hill radius.
The historical example of the Vatican's insistence on a geocentric (Earth-centered) model of the solar system didn't change the actual orbit of the Earth around the Sun. Similarly, the new JPL Horizons model won't alter the true trajectory of 3I/ATLAS. We'll know for sure whether the perijove distance aligns with the Hill radius as 3I/ATLAS gets closer to Jupiter on March 16, 2026. Data from spacecraft like Juno, Juice, or Psyche will be invaluable in resolving this question.
Because 3I/ATLAS was hidden from terrestrial telescopes during its perihelion passage – when it experienced the most significant non-gravitational acceleration – we may only be able to tightly constrain the integrated drift of 3I/ATLAS from its purely gravitational path, but not its radial dependence close to perihelion.
But what if this rare coincidence – the perijove distance matching the Hill radius – actually materializes? It could be a signal, a sign of something artificial. In that scenario, 3I/ATLAS might be releasing technological devices as artificial satellites of Jupiter, perhaps at Jupiter's Lagrange points L1 and L2 on the Hill sphere, where minimal orbital corrections and fuel are needed. These Lagrange points are gravitationally stable locations where objects tend to accumulate.
The statistical probability of such a close match between the perijove distance and the Hill radius within Jupiter's orbit is less than 0.00004. If the non-gravitational acceleration was indeed necessary to achieve this alignment, it would be the most remarkable anomaly of 3I/ATLAS to date, adding to the list I've compiled here: https://avi-loeb.medium.com/anomalies-of-3i-atlas-organized-by-likelihood-af20fb3b6d21. The final verdict will ultimately be determined by the data and posted on the JPL Horizons website, reminding us that science is a continuous process, not a set of pronouncements from authorities.
So, what do you think? Is this just a cosmic coincidence, or could there be something more to the story of 3I/ATLAS? Could this object be exhibiting behavior beyond what we understand through natural phenomena? Is it possible the assumptions in the models are missing key elements? I encourage you to share your thoughts and opinions in the comments below!
