The History of Exoplanets
For hundreds of years, humans have wondered if there were planets around other stars, but it has really only been in the last few decades that we have possessed the tools to go about detecting them. Of course, it wasn’t known whether these extrasolar systems would resemble ours or indeed whether we may go even further and detect life (or the signs of life) in these systems.
In the sixteenth century the Italian philosopher Giordano Bruno (Figure 1), suggested that the distant stars were similar to our Sun and therefore may harbour planets of their own. This view was also supported by Isaac Newton who wrote "... and if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One."
Early claims to have detected exoplanets were made in the 19th century, notably by William Jacob. In 1855, he saw deviations in the orbits within the nearby 70 Ophiuchi binary star system. The work of Thomas See later that century appeared to confirm this with a proposed 36 year orbital period of a dark object around one of the known stars. These theories have since been discredited, although that hasn’t stopped the “planets” around these stars appearing in science fiction works such as Star Trek and Dune.
The first time we actually detected an exoplanet (orbiting a white dwarf called van Maanen 2 which some scientists believe may have a low-mass planetary companion) may have been as long ago as 1917 as detailed by NASA’s JPL.
In 1952, Russian-born Otto Struve proposed that both Doppler spectroscopy and the transit method could detect massive planets that were close to their parent stars.
While the jury is still out on van Maanen 2, the first ‘real’ detection came in 1988 though it took until 2002 for the existence of these planets to be confirmed in the binary star Gamma Cephei Ab.
Soon after, in 1992, came the first true detections with the discovery of objects orbiting the pulsar PSR B1257+12.
Read more about the first discoveries.