'The idea is to consider the moon’s surface as a fishing net for interstellar objects collected over time," wrote Loeb, who's a member of the President's Council of Advisors on Science and Technology. He said that some of these interstellar objects might have originated from the habitable environments around other stars and delivered amino acids – the building blocks of life – to the moon.
According to Loeb, the moon is an ideal place to look for signs of alien life because it is geologically inactive. This means that the lunar surface likely preserved any intriguing clues brought by asteroids and other astrophysical sources instead of burying them deep under the surface. On Earth, active volcanism covers up impact craters and alters the material brought by meteorites.
"Serving as a natural mailbox, the lunar surface collected all impacting objects during the past few billions of years," Loeb said. He added that the absence of a lunar atmosphere also prevents meteors from burning up, which will otherwise eliminate any interesting hitchhikers upon impact.
While most of the moon's craters were likely caused by objects from within the solar system, objects from interstellar space can also make their way into the solar neighborhood. In 2017, for instance, researchers discovered that the solar system was visited by a mysterious object called 'Oumuamua.
What's strange about this interstellar visitor is that it resembled both a comet and an asteroid but lacks the defining characteristics of either rock. In fact, it was speculated that 'Oumuamua might be a lost piece of advanced alien technology. Loeb said that objects like 'Oumuamua portend extraterrestrial pay-dirt on the moon, and studying them can help inform how much interstellar debris may be lurking on the lunar surface.
"With this calibration at hand, one can calculate the amount of interstellar material that has collected on the moon’s surface over its history," wrote Loeb.
He noted that based on current measurements of the flux (amount of energy) of interstellar objects, the lunar surface potentially harbors up to 30 parts per million of interstellar debris and a few parts per hundred billion of amino acids. Rocks that originated from elsewhere in the cosmos can be identified by studying their oxygen, carbon or nitrogen content, according to Loeb.
Loeb raised the possibility that microfossils of extinct alien life are lurking on the lunar surface, as meteorites as old as 3.4 billion years have been found on Earth. But he's more excited about the possibility of finding traces of alien technology. These, according to Loeb, will serve as "a letter from an alien civilization saying, 'We exist.'"
"Without checking our mailbox, we would never know that such a message arrived," Loeb said. He's optimistic that breakthrough findings are just around the corner, especially as the United States and China are planning to establish a permanent human presence on the moon. (Related: What did China's moon lander see on the far side of the moon?.)
For instance, the National Aeronautics and Space Administration's Artemis mission involves plans of building a lunar base and sending astronauts to the moon at least once every year. These efforts can advance space research and lead to new scientific discoveries.
Cosmic.news has more on the search for alien life.