Ever since interstellar object 3I/ATLAS streaked into our solar system , astronomers have been scrambling to understand how this likely comet got here—and more importantly, perhaps, where it came from.

As only the third interstellar object ever discovered, 3I/ATLAS offers a rare chance to study remnants of solar systems beyond our own, briefly bringing the distant galaxy within reach.

But before we get into the new study, imagine the Milky Way as a kind of celestial sandwich: Inside is a thin disk, full of stars and dust, encased by a puffy thick disk, which has different chemistry and composition to the thin disk and which contains older stars. Early observations of 3I/ATLAS pointed to an origin point in that more ancient, puffy layer, but a new study posits a totally different theory

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