What if a passing interstellar visitor brushed right up against Jupiter’s “zone of control” so precisely that it almost looks intentional? That’s the puzzle scientists are now wrestling with as they track the strange, non‑gravitational behavior of the object known as 3I/ATLAS.
Ongoing tracking of 3I/ATLAS
The interstellar object 3I/ATLAS is being closely monitored through NASA’s JPL Horizons system, where Davide Farnocchia regularly updates its measured non‑gravitational acceleration. These non‑gravitational forces are tiny pushes that go beyond what gravity alone can explain, often caused by material evaporating off the object’s surface.
On October 30, 2025, the parameter that describes the radial (Sun‑directed) non‑gravitational acceleration, called A1 and scaled to a distance of 1 astronomical unit (1 au) from the Sun, was given as $$1.6 imes 10^{-6}$$ au per day². By November 24, that number had dropped by a factor of four, down to $$4 imes 10^{-7}$$ au per day², as reported in coverage referencing an article on Medium. In simple terms, the apparent extra “push” along the radial direction had been revised downward significantly over just a few weeks.
A startling match with Jupiter’s Hill radius
Earlier analysis highlighted a striking coincidence involving 3I/ATLAS’s closest approach to Jupiter, or perijove, which is predicted for March 16, 2026. For that date, the minimum perijove distance was forecast to be 53.445 million kilometers, with an uncertainty of about ±0.06 million kilometers. That value essentially matched, within one standard deviation, Jupiter’s Hill radius at that same time, which is about 53.502 million kilometers.
The Hill radius marks the boundary inside which Jupiter’s gravity dominates over the tidal influence of the Sun. If a small object or satellite orbits inside this radius, Jupiter can hold on to it gravitationally; if it sits outside, the Sun’s gravitational pull tends to strip it away over time. So, the idea that 3I/ATLAS would skim Jupiter at nearly exactly this boundary is both scientifically intriguing and, to some, suspiciously neat.
Silence, then a major model revision
Surprised by how closely the predicted perijove distance lined up with Jupiter’s Hill radius, the author of the original analysis emailed Davide Farnocchia to flag this improbable alignment. No reply ever came. But within just a few days, the value of A1 listed on the JPL Horizons page was sharply revised down again, this time by about a factor of six, to $$6.8 imes 10^{-8}$$ au per day².
Along with that numerical change came a shift in the assumed physical model behind the non‑gravitational acceleration. Instead of using a steeper radial dependence, JPL Horizons adopted a simple inverse‑square law with distance from the Sun, proportional to $$1/r^2$$. This form is physically reasonable for an object whose outgassing is dominated by the sublimation of carbon dioxide (CO₂) ice inside about 5 au from the Sun, because solar heating there tends to scale roughly with $$1/r^2$$. The new approach replaced an earlier, steeper profile designed for water (H₂O) ice sublimation, which was based on classic modeling work by Brian Marsden and colleagues.
Updated perijove distance—but is it convincing?
Using this revised $$1/r^2$$ model, JPL Horizons now predicts a slightly different closest‑approach distance to Jupiter for 3I/ATLAS: 53.587 million kilometers, with an uncertainty of ±0.045 million kilometers. This value puts the object just outside Jupiter’s Hill radius on March 16, 2026, rather than essentially right on top of it.
However, this forecast depends heavily on how the non‑gravitational acceleration is distributed with distance from the Sun. The $$1/r^2$$ framework leans on contributions from earlier phases of the object’s journey at larger heliocentric distances to explain the observed deviations from a purely gravitational trajectory. If those assumptions about how the force scales are off—especially near perihelion—then the predicted perijove distance could shift again.
Why the 1/r² model likely falls short
There are good reasons to suspect that the simple $$1/r^2$$ description does not fully capture what 3I/ATLAS is doing. Observations indicate that the object brightened around perihelion far more than such a smooth inverse‑square model would suggest. Since brightness here is tied to how much material is being ejected (more gas and dust means more sunlight scattered), that extra brightening hints at a stronger, more sharply increasing non‑gravitational push near perihelion.
If the radial dependence of the acceleration is adjusted to reflect this stronger activity close to the Sun, the resulting orbital solution would likely move the predicted perijove distance back toward the Hill radius value. In other words, once the model better matches the real physics of the outgassing, the “too‑good‑to‑be‑true” match between perijove and Hill radius may reappear.
Luminosity evolution and steeper radial profiles
Evidence for a steeper profile comes from how the brightness (luminosity) of 3I/ATLAS changed over time. A Hubble Space Telescope image obtained on July 21, 2025 showed that the light from the object was dominated by its surrounding coma—the diffuse cloud of gas and dust being released. When the brightness is mostly due to the coma, it acts as a rough tracer of mass loss, assuming the total scattered sunlight scales with the mass of the ejected material.
A recent preprint by Marshall Eubanks and collaborators reported the evolution of this luminosity over the object’s approach. Earlier work by Qicheng Zhang and Karl Battams suggested that, inside about 2 au from the Sun, the brightness followed an extremely steep radial trend, roughly proportional to $$1/r^{7.5}$$, as 3I/ATLAS headed toward its perihelion distance of 1.36 au on October 29, 2025. If such a steep dependence also applies to the non‑gravitational acceleration, then using it in the dynamical model would naturally alter the predicted perijove distance, nudging it back into closer agreement with Jupiter’s Hill radius.
Models vs. reality: a historical reminder
The situation invites a philosophical comparison: the Vatican’s historical insistence that Earth sat motionless at the center of the cosmos never altered Earth’s actual orbit around the Sun. Likewise, adjusting the mathematical model in JPL Horizons does not change the real path 3I/ATLAS is following through space. The object will go where physics dictates, regardless of what any official fit or parameter choice claims.
Over the coming months, as 3I/ATLAS approaches its March 16, 2026 perijove, fresh measurements will reveal whether the true closest‑approach distance genuinely lines up with Jupiter’s Hill radius. High‑precision astrometric data from spacecraft such as Juno, Juice, or Psyche could prove especially valuable, since they can track the object’s position with far greater accuracy than many ground‑based telescopes.
The observational blind spot near perihelion
A key complication is that 3I/ATLAS passed behind the Sun from the viewpoint of Earth‑based telescopes during its perihelion passage. Ironically, that is exactly when it likely gained most of its non‑gravitational acceleration, due to peak heating and maximum outgassing. Because of this solar glare, observers have a good handle on the total net deviation from a purely gravitational orbit, but only a weak constraint on how that deviation was distributed with distance—particularly in the critical region close to perihelion.
This observational gap leaves room for multiple radial‑dependence models to fit the available data similarly well, at least for now. The real test will come as more post‑perihelion astrometry is collected and integrated into updated orbital solutions, narrowing down which physical explanation best matches reality.
Could this be a technological signature?
Here is where the story becomes truly provocative. If the rare coincidence between 3I/ATLAS’s perijove distance and Jupiter’s Hill radius holds up under better data and more refined modeling, some researchers argue it might hint at a technological rather than purely natural origin. In such a speculative scenario, 3I/ATLAS could act as a carrier that releases artificial devices into stable orbits around Jupiter.
These hypothetical devices might be deployed as artificial satellites parked near Jupiter’s Lagrange points L1 and L2 on the edge of the Hill sphere. Those locations are gravitational sweet spots where station‑keeping (making small corrections to stay in place) requires minimal fuel. From a “technological design” perspective, they would be efficient vantage points for long‑term monitoring or other activities.
How unlikely is this alignment?
Within the full width of Jupiter’s orbit around the Sun, estimates suggest that the probability of 3I/ATLAS passing at a perijove distance so closely matched to Jupiter’s Hill radius is less than 0.00004. That is a tiny statistical likelihood if the alignment is purely random. If, on top of that, the object needed a carefully tuned non‑gravitational acceleration to achieve such a match, then this would become the most extraordinary anomaly yet in the growing catalog of unusual properties attributed to 3I/ATLAS.
However, even an extremely small probability event can occur naturally in a vast universe with countless objects and encounters. This is one of the central controversies: does such a rare configuration meaningfully point to intent, or is it just a cosmic coincidence that looks suspicious because humans are very good at spotting patterns after the fact?
Science as an open, ongoing process
Whatever the outcome, the final, authoritative orbital solution for 3I/ATLAS will ultimately appear in the JPL Horizons database. But that listing will not represent a decree from on high; it will simply be the best current fit to all available data. This underscores a fundamental point: science is always provisional and evolving, guided by evidence rather than by institutional authority or press‑conference narratives.
If future measurements show that the perijove distance truly coincides with Jupiter’s Hill radius, the debate over possible artificial influences will intensify. If, instead, the match fades as models and data improve, the event will still serve as a powerful case study in how scientists test, refine, and sometimes abandon intriguing hypotheses.
Your turn: coincidence or clue?
So, what do you think: is the near‑perfect match between 3I/ATLAS’s predicted perijove distance and Jupiter’s Hill radius a cosmic roll of the dice, or could it be a subtle hint of something engineered? If non‑gravitational forces turn out to be finely tuned, would you lean toward a natural explanation, or consider the possibility of a technological signature worth taking seriously? Share where you stand—do you see this as over‑interpretation of noisy data, or as a puzzle humanity shouldn’t ignore?