Why can pulsar timing detect planets with very small masses?

Pulsar timing is an exceptionally sensitive method for detecting extrasolar planets because it relies on the extreme regularity of pulsar emissions. Pulsars are rapidly rotating neutron stars that act as highly accurate cosmic clocks, emitting pulses of radiation at precise intervals.12

When a planet orbits a pulsar, it causes the pulsar to wobble, which creates minute, periodic variations in the arrival times of these pulses at a radio telescope on Earth. Because the underlying pulse timing is so stable, even the tiny gravitational tugs exerted by very low-mass planets—as small as the mass of Earth’s Moon—can be detected through these timing shifts. This sensitivity is significantly higher than that achieved when observing pulsating normal stars, where only giant planets can typically be identified. This method was famously used to discover the first extrasolar planets in 1992 around the pulsar PSR 1257+12.342