Abstract
The formation and characterization of hydrogen trioxide have fascinated scientists for more than a century, due to its role as a prototype model for oxygen-chain bonding and as a key transient in antibody-catalyzed oxidation reactions relevant to the origin of life. However, the abiotic formation pathways to hydrogen trioxide have remained elusive. Here, we demonstrate in laboratory simulation experiments that hydrogen trioxide effectively forms in water-molecular oxygen ice analogs at temperatures as low as 5 kelvin under exposure to proxies of galactic cosmic rays. Exploiting synchrotron vacuum ultraviolet photoionization reflectron time-of-flight mass spectrometry, hydrogen trioxide along with hydrogen peroxide and the hydroperoxyl radical was identified during the temperature-programmed desorption of the irradiated ices. This abiotic synthesis expands the oxidant inventory on interstellar grains, icy moons, and Kuiper belt objects, offering a plausible source of essential oxidizers for prebiotic chemistry in space.