Interstellar Comet 3I/ATLAS Is Erupting, Pulsing and Powering Planetary‑Defense Drills Ahead of Its December 19 Flyby
Astronomers report interstellar comet 3I/ATLAS is erupting with cryovolcanic activity and shows a 16.16-hour brightness cycle. Radio signals from the object are confirmed natural. The comet will pass closest to Earth on December 19, 2025, at 1.8 AU. A UN-led planetary defense drill is using 3I/ATLAS as a practice target.