Using the Atacama Large Millimeter/submillimeter Array (ALMA), scientists have discovered that the interstellar invader comet 3I/ATLAS formed in a much colder region of the Milky Way than our solar system.
The discovery came about when scientists made the first-ever measurement of so-called semi-heavy water (or deuterated water) for an object that originated beyond the solar system. Deuterated water refers to water in which one hydrogen atom is replaced with deuterium, a heavy hydrogen isotope that has an atomic nucleus composed of one proton and one neutron. ALMA's measurements of deuterated water revealed that 3I/ATLAS contains around 30 times as much semi-heavy water as is found in comets that originate in the solar system.
