LGM-1: Jocelyn Bell's "little green men"

In 1967, doctoral student Jocelyn Bell was poring over miles of chart paper printed by a radio telescope built from posts and wires on the outskirts of Cambridge. Amid the noise, she spotted a strange mark: pulses repeating with clockwork precision, every little more than a second. Nothing known in the sky behaved that way.

The team went as far as naming the source LGM-1, short for "little green men," half as a joke, half seriously. When Bell found a second, similar signal in another part of the sky, the alien hypothesis lost steam: two civilizations broadcasting the same way seemed unlikely. The explanation came soon after. They were pulsars, the remains of collapsed stars spinning extremely fast. The discovery earned the 1974 Nobel Prize, awarded to her supervisor Antony Hewish and to Martin Ryle, but not to her, a decision that remains controversial to this day.