The Discovery of the First Exoplanets

This chapter deals with the discovery of the first extrasolar planets around normal stars. This discovery took place in the mid-1990s thanks to the analysis of periodic Doppler shifts in stellar spectra and turned out to be a landmark achievement, in that it established a new field of research that is growing at full speed since then, and at the same time, it answered a question—do other worlds exist in the cosmos? —that dates back to ancient times. This major result was made possible by the impressive improvement in Doppler analysis techniques during the second half of the twentieth century, until the precision boosted to values suitable to detect massive planets in close-in orbits. In the late 1980s, two objects came to the limelight: HD 114762 b and γ Cep b. They were suspected to be exoplanets, but it was not possible to rule out alternative explanations, so no undisputable discovery could be claimed. A few years later, in 1995, the discovery of 51 Peg b was announced and confirmed as the first secure one. However, the features of this planet were quite weird as compared to those of the planets of the Solar System, as it was massive and very close to its parent star. Its discovery overturned the previously widespread idea that other systems had to be made like ours and opened the floodgates to the spotting of many other planets. This chapter tells this story, mainly dwelling upon the historical and epistemological aspects.