Study estimates interstellar comet could be up to 12 billion years old but notes younger-age possibilities

Comet 3I/ATLAS, the third confirmed interstellar object observed passing through the solar system, may be up to 12 billion years old, according to isotopic measurements published Monday in the journal Nature. The comet was first observed in July 2025.

Data from the James Webb Space Telescope and the ALMA observatory in Chile showed it contains approximately 10 times more deuterium than typical solar-system comets.

The measurements indicate the object formed in an environment at roughly minus 243 degrees Celsius and has an elemental composition unlike any solar-system body. " He noted possible edge-case scenarios that could explain the chemical composition without requiring extreme age.

NASA released Hubble Space Telescope images of 3I/ATLAS on 21 July 2025 when it was approximately 277 million miles from Earth and on 30 November 2025 when it was about 178 million miles from Earth.

Mars orbiters captured images in October 2025 at roughly 18. The two prior interstellar objects, 1I/'Oumuamua observed in 2017 and 2I/Borisov observed in 2019, lacked sufficient brightness for isotopic measurements. " SETI reported last month it found "no evidence of extraterrestrial technology" on the comet.

Avi Loeb said all possibilities, including non-cometary origins, should remain open until further data are obtained. Peter Veres stated future observations will become increasingly difficult as the comet leaves the solar system and will never return.