BY:SpaceEyeNews.
Interstellar comet 3I/ATLAS is not just passing through. It’s carrying a question that sounds simple, but behaves like a cosmic puzzle: where is the 3I/ATLAS origin? We can measure its speed. We can map its incoming direction. We can even rewind its motion through the Milky Way using Gaia’s star catalog. Yet the deeper scientists dig, the more the “home address” starts to look like a list of suspects, not a single answer.
In this SpaceEyeNews breakdown, we’ll walk through the three most-discussed candidate systems that show up when researchers trace 3I/ATLAS backward in time. Each suspect comes with real data. Each also comes with a catch.
3I/ATLAS origin clue #1: it arrived on a truly unbound path
Astronomers confirm an interstellar visitor by checking one thing first: is it gravitationally bound to the Sun? For 3I/ATLAS, the answer is a clear no.
Early observations show an extremely hyperbolic orbit and an incoming speed around 58 km/s, with eccentricity around 6.1 and a steeply tilted trajectory (inclination near 175°). Those numbers appear in early characterization work led by Seligman and collaborators. orbi.uliege.be
NASA’s tracking also makes the “visitor” status unambiguous. When you trace the orbit into the past, 3I/ATLAS clearly comes from outside the Solar System. NASA also notes it poses no threat, staying far from Earth (closest approach about 1.8 AU) and reaching perihelion around 1.4 AU. NASA Science
All of that sets the stage for the next step: if it’s interstellar, can we trace it back to a home system?
How scientists try to solve the 3I/ATLAS origin puzzle
Gaia DR3 turns the Milky Way into a rewindable crime scene
The modern hunt for an interstellar object’s origin relies heavily on Gaia. Gaia DR3 provides positions, distances, and motions for huge numbers of stars. Researchers take 3I/ATLAS’s best-known orbit today, then integrate it backward through a Galactic gravity model. They do the same for stars nearby in the Milky Way. Then they search for close flybys in the past.
One detailed effort by Yiyang Guo and colleagues propagated 3I/ATLAS and tens of millions of Gaia stars, searching for past close passages. They report 25 encounters with median distances under 1 parsec, but also stress a key limitation: the relative speeds are very high, which makes “this star ejected it” hard to justify under common mechanisms.
A separate study by Pérez-Couto and collaborators ran a similar backward search and found 93 nominal encounters (62 high-confidence) in the last 10 million years, but concludes none meaningfully perturbed the object’s path. In other words, recent nearby stars did not “steer” it into our neighborhood in any strong way. ar5iv
Why the trail gets fuzzy fast
Even with Gaia, orbit backtracking has a built-in problem. Tiny uncertainties in a star’s radial velocity, or in the comet’s orbit, expand as you integrate millions of years into the past. Then there’s the bigger issue: 3I/ATLAS likely spent billions of years traveling. Over that time, many weak gravitational tugs can blur a clean breadcrumb trail.
So instead of a single smoking gun, researchers often end up with a shortlist of “best encounters”—systems that pass close enough, at the right time, to be worth investigating.
That’s where our three suspects enter the story.
Suspect #1 for 3I/ATLAS origin: the G 137-55 / G 137-54 ultra-wide binary
Why it shows up as the strongest “perturber”
In Guo et al.’s encounter list, one system stands out. It’s an ultra-wide binary made of two M-dwarf stars: G 137-55 and G 137-54 (Gaia DR3 1197546390909694720 and 1197546562708387584). Gaia data imply a projected separation of about 1358 AU, which is huge for a bound pair.
Guo et al. describe this binary as the strongest gravitational scattering perturber along the past segment they studied. That doesn’t mean it launched 3I/ATLAS. It means that, among the close encounters they found, this system had the best combination of mass and proximity to bend the comet’s path even slightly.
The team reports that the encounter distance between the binary’s barycenter and 3I/ATLAS could have been about 0.242 pc, around 1.64 million years ago, at a relative speed of about 28.39 km/s.
What makes ultra-wide binaries interesting
Ultra-wide binaries matter because they can behave like weak “slingshot” systems over long timescales. They also often live in environments where gravitational nudges from passing stars slowly reshape their orbits. That dynamical instability can stir up distant comet reservoirs.
In principle, a binary-plus-planets architecture can eject small bodies. That’s why binaries show up in interstellar object origin discussions.
Why it’s still unlikely
Here’s the catch. The same paper that flags the G 137-55/G 137-54 pair as the strongest perturber also says the encounter speed is too high for typical ejection stories. Guo et al. note that common binary ejection mechanisms struggle to explain an encounter speed above 20 km/s for a plausible “home system” link.
So Suspect #1 is strong in one sense: it’s the best “gravity nudge” they found. But it is weak as a birthplace candidate.
Suspect #2 for 3I/ATLAS origin: AT Mic A / AT Mic B, a young M-dwarf binary
Why AT Mic looks tempting at first
Guo et al. also call out AT Mic A and AT Mic B (Gaia DR3 6792436799475128960 and 6792436799477051904) as a notable binary encounter candidate.
AT Mic is intriguing because it’s not just two small stars. It’s an active system. The paper notes rapid rotation and strong X-ray and ultraviolet activity, plus an ALMA-detected cold dust belt—signals of a lively, debris-rich environment. In plain terms: it’s the kind of neighborhood where comets and planetesimals can be plentiful.
Even better, AT Mic belongs to the Beta Pictoris moving group, with an age on the order of tens of millions of years and a distance around 9.8 pc. Youth matters because young systems can experience chaotic clearing, and that clearing can eject material.
Why it’s still unlikely
The same paragraph that makes AT Mic sound promising also undercuts it.
Guo et al. point out that AT Mic’s space motion sits very close to the Local Standard of Rest (LSR). That is far below 3I/ATLAS’s speed relative to the LSR. They also cite other work suggesting 3I/ATLAS fits better with an older Galactic population than a ~25 Myr system.
So AT Mic has the “right vibes” as an ejector—active, dusty, dynamic. But its kinematics and age context do not match well with what 3I/ATLAS seems to represent.
Suspect #3 for 3I/ATLAS origin: a G-type star encounter candidate (G3V)
A Sun-like star is an efficient ejector
The third suspect is a very different kind of system: a G-type main-sequence star. In Guo et al.’s list, Gaia DR3 6570039342736534784 is classified as G3V in SIMBAD, meaning it’s broadly Sun-like.
Why does that matter for the 3I/ATLAS origin discussion? Because Sun-like stars commonly host planetary systems, and giant planets are especially effective at ejecting small bodies. In fact, Guo et al. explicitly note that a G-type star could plausibly host giant planets, and that massive planets boost ejection efficiency through repeated gravitational scattering.
So if you wanted a generic “best engine” for producing interstellar comets, a star with big planets is a strong candidate.
Why it’s still unlikely
Again, the catch is speed and geometry.
Guo et al. group this G3V star with several other encounter candidates and conclude that, taken together, their encounter speeds and stellar masses make it unlikely any served as the host. High relative velocity means the comet did not linger in a way that looks like a clean ejection event from that system.
So Suspect #3 is plausible in theory, but weak in the specific traceback evidence.
What the statistics suggest about the 3I/ATLAS origin
At this point, the puzzle shifts. Instead of asking “Which star?” researchers often ask: “Which Galactic population does it most resemble?”
Thin disk, thick disk, or the boundary zone?
Guo et al. argue that a thin-disk origin is strongly favored, because the thin disk’s velocity distribution matches 3I/ATLAS well and because the thin disk dominates the local stellar number density.
Pérez-Couto et al. reach a compatible conclusion from a different angle. They show that 3I/ATLAS is kinematically consistent with a thin-disk population, even though it has a large peculiar velocity. ar5iv
Other commentary has discussed a thick-disk possibility. A popular write-up of ongoing research notes that some models place it in a transition region between thin and thick disk, and that kinematics alone cannot “prove” the region beyond doubt. IFLScience
Age adds another twist
Kinematics can also hint at age. An ApJ Letter indexed by ADS reports a kinematics-based age estimate that places 3I/ATLAS as likely several billion years old (on the order of a few to ~10+ Gyr in the reported posterior range). ui.adsabs.harvard.edu
That kind of age would fit an object that has wandered for a very long time, making a precise “home star” match harder.
So can we identify the exact 3I/ATLAS origin star?
Not with confidence. And the reason is not a lack of effort.
Guo et al. find multiple close encounters but note that none looks like a plausible host under common ejection mechanisms, mainly due to high encounter speeds.Pérez-Couto et al. find many encounters too, yet conclude none produced meaningful perturbations that explain the current path. ar5iv
That leaves us with a more honest answer: we can describe the 3I/ATLAS origin statistically better than we can name it geographically. The evidence points toward the Milky Way’s disk population, with at least one major analysis strongly favoring a thin-disk origin.
In that context, the “three suspects” are best understood as clues, not conclusions:
- A wide M-dwarf binary that likely gave the strongest recent gravitational nudge.
- A young, active M-dwarf pair that looks ejector-friendly, but mismatches the object’s kinematic story.
- A Sun-like G3V star that fits planet-driven ejection theory, but fails on encounter specifics.
And that may be the real lesson. The Milky Way is not a set of isolated planetary systems. It is a connected dynamical ecosystem. Objects like 3I/ATLAS are the receipts.
Main sources (for citation and further reading)
- Pérez-Couto et al. (2025), “3I/ATLAS: In Search of the Witnesses to Its Voyage” (arXiv:2509.07678) — 93 encounters / 62 high-confidence, weak perturbations, thin-disk consistency. ar5iv
- Seligman et al. (2025), ApJ Letters, “Discovery and Preliminary Characterization of a Third Interstellar Object: 3I/ATLAS” — early physical/orbital characterization numbers. orbi.uliege.be
- NASA Science: “Comet 3I/ATLAS” — discovery context, observing notes, and safe flyby distances. NASA Science
- ADS entry: Taylor (2025) ApJ Letter on kinematics-based age implications — age inference via kinematics. ui.adsabs.harvard.edu