Interstellar comet 3I/ATLAS may be nearly 12 billion years old — so ancient its star system may no longer exist

The interstellar comet that recently dominated headlines, 3I/ATLAS, could be between 10 and 12 billion years old, a new assessment of the comet's isotopic composition has shown. This so-called "invader" in our solar system is only the third object on record to enter our cosmic neighborhood from beyond.

When it was discovered in 2025, 3I/ATLAS was speeding in at 36 miles (58 kilometers) per second relative to the sun. It is the fastest comet ever seen, vastly exceeding the velocities of its predecessors 1I/'Oumuamua and 2I/Borisov. And according to theory, the faster an interstellar object is travelling, the older it must be because it must have experienced multiple space-object encounters and gravitational slingshots with other stars that would accelerate it to a high velocity.

When in a close binary system with another star, a white dwarf can steal so much material that it ignites a thermonuclear explosion on its surface. We call this a nova, and such events are prodigious producers of carbon-13. A rapid burst of nova explosions is expected to have therefore occurred during the first four billion years of the Milky Way's history.