I/ATLAS is definitely a comet, not an alien spacecraft, but it is only the third confirmed interstellar object detected in our solar system, and may be as much as 7 billion years old, so it is still pretty cool and worth checking out.

Interstellar comet 3I/ATLAS is set to make its closest approach to Earth on December 19, giving skywatchers a rare chance to spot a visitor from another star system.