Why did Michel Mayor and Didier Queloz receive the 2019 Nobel Prize in Physics?

Michel Mayor and Didier Queloz were awarded one half of the 2019 Nobel Prize in Physics for their discovery of the first known extrasolar planet orbiting a Sun-like star.12

In 1995, using the ELODIE spectrograph at the Haute-Provence Observatory, they detected 51 Pegasi b by measuring the radial velocity of its host star. This planet, which has a mass about half that of Jupiter and an orbital period of only 4.23 days, was the first "hot Jupiter" ever discovered.1234

This groundbreaking finding challenged existing theories of planetary system formation—which were based on the solar system—and effectively launched the modern field of extrasolar planet research. Their work demonstrated that planets unlike those in our own solar system exist, paving the way for the discovery of thousands of other extrasolar planets in the decades that followed.124