The comet 3I/ATLAS is just the third visitor from beyond our Solar System that humanity has ever observed, its unusual brightness offering scientists an unprecedented opportunity to study something that came from elsewhere in the galaxy.After being spotted in July last year, the space rock prompted excitement online, with one prominent Harvard researcher speculating it could be an alien spacecraft -- a theory that NASA shot down.Now, observations by the world's most powerful telescopes are revealing more about the unique comet. According to a new study published in the journal Nature, 3I/ATLAS could be up to 12 billion years old. Our Solar System is believed to have formed around 4.5 billion years ago.Lead study author Martin Cordiner of NASA's Goddard Space Flight Center told AFP that "maybe it's the oldest object to have been observed in our Solar System".However there could be "edge-case scenarios" that offer other explanations for the comet's unusual chemical composition, he added. The new research is based on the comet's ratio of chemical elements called isotopes detected by the James Webb space telescope and the ALMA observatory in Chile.These measurements "reveal an elemental composition unlike any Solar System body", the study said.Relic from 'cosmic noon'?Compared to comets in our Solar System, 3I/ATLAS had around 30 times more deuterium, a type of hydrogen commonly seen in heavy water, according to a NASA statement."That high abundance of heavy water can only really happen, according to our understanding of astrochemistry, in a very cold environment," Cordiner explained.This means the comet is also likely among the coldest objects ever seen in our Solar System, the isotopic evidence suggesting it formed in an environment that was minus 243 degrees Celsius.