In 1992, astronomers looked towards pulsar PSR B1257+12. The radio emissions of pulsars usually have such a regular beat they’ve been called cosmic clocks. But in this case, something was wrong. Every so often, the pulsar’s regular 6.22ms-long pulse would be ever so slightly off.
After careful study, astronomers Aleksander Wolszczan and Dale Frail realised the irregularities had their own rhythm. The pattern was a perfect fit for what would happen if the pulsar’s precise timing was being upset by the gravitational pull of a pair of planets. It was the first strong evidence of the presence of exoplanets in orbit around another star.
The discovery alone was a great achievement, but the real shock came when they worked out the size the planets would need to be to create the effect seen: four times the mass of Earth.
“It’s interesting, because in our Solar System we have this big gap,” says Eliza Kempton, who researches exoplanets at the University of Maryland.
