19th December 2025 – (Hong Kong) An interstellar visitor is traversing our Solar System, presenting a rare scientific opportunity with no risk to Earth. Discovered on 1st July 2025 by NASA’s ATLAS survey telescope in Chile, Comet 3I/ATLAS is thought to have originated in interstellar space, the vast region between star systems beyond the Sun’s magnetic influence. Its “3I” designation marks it as only the third confirmed interstellar object after 1I/’Oumuamua and 2I/Borisov.
The comet made its closest approach to Earth at about 1am EST on 19th December, passing at roughly 168 million miles, or around 270 million kilometres, more than 700 times the Earth–Moon distance. NASA has stressed there is no danger of impact. It was not visible to the naked eye, and observers were encouraged to seek views through telescopes at local observatories or star‑watching events. The best prospects were before dawn, looking east to north‑east beneath the star Regulus in the constellation Leo, where it appeared around magnitude 11–12 in small telescopes. For those unable to watch directly, the Virtual Telescope Project planned a free livestream from Manciano, Italy, beginning at 11pm. ET on 19th December, weather permitting after rain postponed an earlier broadcast.
3I/ATLAS is travelling on a hyperbolic trajectory, moving too fast to be captured by the Sun’s gravity. It entered the inner Solar System from the direction of Sagittarius, likely formed around another star, and has drifted for millions or even billions of years. It reached perihelion on 30 October inside Mars’s orbit at about 130 million miles from the Sun, passed behind the Sun, re‑emerged in early December, and will continue outward, exiting the Solar System permanently.
Multiple independent observations indicate the object is a natural comet composed chiefly of ices, including water and carbon dioxide, with a small rocky nucleus. As it warms near the Sun, gases escape to form a glowing coma and tail; any greenish tint is a routine consequence of its chemistry. Its well‑mapped, hyperbolic course and a closest‑approach distance of about 1.8 astronomical units rule out any collision risk. While speculative ideas have circulated, researchers have found no robust evidence of unusual behaviour.
Scientists regard 3I/ATLAS—also known as C/2025 N1—as a rare chance to study material from beyond our Solar System, refining understanding of comet chemistry, dynamics and the formation of distant planetary systems. Despite occasional sensational claims, US and European space agencies report the object looks and behaves exactly like a comet, and astronomers emphasise that extraordinary claims require extraordinary evidence, which has not been forthcoming. As only the third confirmed interstellar object, it offers a unique, entirely safe glimpse of another star system as it speeds past and disappears into deep space.
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