Later in December, the 3I/ATLAS interstellar comet will get as close to Earth as it ever will. Here's what to know.

Near perihelion 3I/ATLAS exhibits non-gravitational acceleration, which requires massive evaporation for a natural comet (as calculated here), whereas preliminary images indicate that the object maintained its integrity and did not break up (as discussed here). Instead, the acceleration might have been produced by an engine.

With 3I/ATLAS just days away from making its closest approach to Earth, agencies around the globe are conducting the largest and most extensive planetary defense drill — with the goal of protecting ourselves against future threats from beyond.

The mysterious interstellar object 3I/ATLAS is approaching Earth, captivating astronomers and the public alike. Discovered in July 2025, 3I/ATLAS is the third object identified as originating from outside our solar system.