Avi Loeb, a Harvard astrophysicist, has suggested that the interstellar object 3I/ATLAS could contain antimatter, which he describes as
"the most efficient fuel" in the universe.
Loeb's idea, presented in a Medium essay, proposes that the interaction between antimatter and solar particles could explain the object's unusual brightness and apparent acceleration.
According to Loeb, if 3I/ATLAS indeed contains antimatter, its passage through the solar wind might generate detectable gamma-ray or X-ray emissions, which could be observed by NASA's Fermi Gamma-Ray Space Telescope.
Author's summary: Avi Loeb suggests 3I/ATLAS may contain antimatter.