Interstellar object 3I/ATLAS could be a 10 billion year old time capsule

On July 1, astronomers spotted an unusual object streaking through the solar system at nearly twice the speed of previous interstellar visitors, Oumuamua and Comet Borisov. The object was quickly confirmed to be an interstellar comet and is believed to have a core (the rocky center of the comet, excluding its coma) of approximately 5.6 kilometers (3.5 miles) and a potential mass of more than 33 billion tons.

The astronomical community continued to track the object as it moved through the solar system and behind the Sun, from our perspective. We may have even seen it using NASA’s Perseverance rover on Mars.

But where does it come from? Luckily for us, gravity is time-reversal symmetrical, and if we know the trajectory of an object, we can work backwards and trace its path. In a new paper submitted to the Astrophysical Journal, but not yet peer-reviewed, a team from the University of A Coruña attempted to do just that.

The team used data from the European Space Agency’s Gaia mission, which produces a three-dimensional map of stars and other objects in the Milky Way and beyond. By tracing the object’s path over 10 million years, the team attempted to identify places where it had had close encounters in the past, within 2 parsecs (6.5 light years) of another star.

“We identify 93 nominal encounters, of which 62 are significant at the 2σ level. However, none of these encounters produced significant disruption,” the team writes in their paper. “The most powerful disruptor Gaia DR3 6863591389529611264 at 0.30 pc and with a relative speed of 35 km s⁻¹only transmitted a speed change of |∆v| ≃ 5 × 10⁻⁴ km s⁻¹ in the orbit of 3I/ATLAS. Our results indicate that no stellar flybys during the last 10 Myr and 500 pc contained in Gaia DR3 can explain the current trajectory of 3I/ATLAS or be associated with its origin.

In short, none of these potential close encounters could explain the origin of 3I/ATLAS and hardly changed its trajectory. But by tracing it back in time, the team thinks it likely came from the thin disk of the galaxy, contrary to an earlier study, which suggested it might have come from the thick disk, given how close it is to the galactic plane.

“Together, all the data indicate that although 3I/ATLAS follows a thin disk orbit in the solar neighborhood, it could nonetheless be an ancient object, consistent with an ejection from a primordial planetesimal disk in an early formed system, or an exo-Oort cloud, and is most likely associated with the transition region between the thin disk and the thick disk, although its origin remains unknown,” concludes the team.

Further study of 3I/ATLAS and other interstellar objects is needed to draw additional conclusions, but this preliminary study suggests that it could be a very ancient object, which could have traveled alone for billions of years until we spotted it near our star. The team suggests the object is about 10 billion years old, making it a time capsule of the formation of the first planetary systems in the galaxy and universe, although we will likely never know its true origin.

“What makes 3I/ATLAS unique is that it allows us to study the evolution of objects from other star systems – something we had only theorized about until now,” added Pérez Couto, a researcher at the Center for Research in Information and Communication Technologies and team leader, in a statement. “Each observation is like opening a window into the past of the Universe.”

The study is published on the arXiv preprint server.