On Earth, the radio spectrum is clogged with signals: communications, television, radar. But on the far side of the Moon, it's quiet. There, Earth's noise is inaudible, and that's exactly where China's Chang'e-4 went to listen to the cosmos for the first time, hunting for alien radio transmissions.
Scientists processed the recordings from its antennas. They were looking for signals that repeat with a precise rhythm, like the ticks of a metronome. Such signals don't resemble natural ones: nature is rarely so punctual. But after careful scrutiny, every suspicious match turned out to be ordinary noise.
The result is empty, but it's not a failure. This is how you test new equipment: you make sure the instrument works and doesn't mistake wishful thinking for reality. In the coming years, new spacecraft with radio receivers will head to the Moon, and then the search for extraterrestrial signals will get truly serious.
Chang'e-4 landed on the Moon in January 2019 and is still operational, even though it was designed to last only a few months.
In the movie Contact, the protagonist hears an alien signal that repeats over and over: it's exactly such periodic signals that were sought in Chang'e-4's data.