The Viking missions to Mars in 1976 did not find organic molecules on the Martian surface, leading scientists to think there might be a strong oxidant converting them to carbon dioxide quickly. However, new research suggests that certain organic acids from meteorites could be present on Mars, but not easily detected by the instruments used. One of these acids, mellitic acid, is stable and could have been generated in significant amounts over billions of years. This means that there might be organic molecules near the surface of Mars, complicating the search for signs of potential Martian life.