A Rare Comet Made History as the Third Known Interstellar Object to Fly Through Our Solar System. Studies Are Now Revealing the Mysterious Conditions in Which It Formed

Jay Bennett | Former Associate Web Editor, Science

Add as preferred source Interstellar object 3I/ATLAS, imaged here with its broad coma of gas and dust, has captivated astronomers since its discovery on July 1, 2025. International Gemini Observatory / NOIRLab / NSF / AURA / Shadow the Scientist Image Processing: J. Miller & M. Rodriguez (International Gemini Observatory / NSF NOIRLab), T.A. Rector (University of Alaska Anchorage / NSF NOIRLab), M. Zamani (NSF NOIRLab) After a visit from beyond the solar system, 3I/ATLAS, the third interstellar object ever detected, is on its way out. Distinct from anything that circles the sun, the icy body has now passed the orbit of Jupiter. Soon it will slip back into the void, never to be seen by humanity again.

The object—a cometlike body enshrouded in gas and dust—was forged in the debris disk surrounding a distant star, providing an extraordinary opportunity for experts to study the building blocks of another planetary system. Astronomers around the world have trained telescopes on this celestial visitor ever since its discovery on July 1, 2025. Both before and after its closest approach to the sun, when the heat of our star vaporized material from its surface, they have analyzed the comet’s composition.