Tong-Jie Zhang

Any device, from a toaster to a smartphone, heats up when operating. This is the inevitable result of energy conversion — there's always a heat trace left, like a hot stove burner after cooking.

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.

3I/ATLAS burst into the Solar System like an uninvited guest, a gift of fate for hunters of extraterrestrial intelligence. This comet-like wanderer from the depths of the Galaxy flew close enough to be heard in all its details — unlike distant exoplanets.