Briefs · Frontier Science
The Oldest Comet We Have Ever Seen Says Goodbye
The oldest comet we have ever seen just said goodbye, and it did so politely.
Interstellar comet 3I/ATLAS made its closest approach to Earth at 1am EST on December 19, 2025, passing about 168 million miles away. That is roughly 1.8 astronomical units, or nearly twice the Earth-Sun distance. It posed no threat whatsoever.
Discovered on July 1, 2025, by the ATLAS telescope in Chile, 3I/ATLAS is only the third confirmed visitor from another solar system, after 1I/’Oumuamua in 2017 and 2I/Borisov in 2019. It passed closest to the Sun on October 29, brightening more than scientists expected. Its path suggests an origin in the Milky Way’s thick disk, making it possibly up to 7 billion years old.
Two spacecraft caught it in November. JUICE pointed five instruments at the comet on November 2, then sent home a grainy NavCam teaser showing a bright nucleus, a glowing coma and a faint plasma tail. Hubble re-observed it on November 30, tracking the comet so precisely that background stars smeared into streaks. The visit is not a threat, but rather a tutorial. A frozen messenger from another star taught us how planets are born elsewhere, then vanished back into the dark.
Read the original at Space.com
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