The hunt for exoplanets has an extensive history. It may come as no surprise that in 1992, scientists were rather bewildered by the first confirmed exoplanetary detections. The first two exoplanets were orbiting the wrong type of star: a pulsar. Pulsars are immensely dense neutron stars at the end of their evolutionary life, which are highly magnetised spinning masses; not the best place to start looking for an exoplanet, but space is full of surprises!

However, the idea of the existence of other worlds really begins a lot earlier than 1992. Whether our Solar System is the only in reality has preoccupied humans for millennia. 

Starting as early as 550 – 600 BC, the ancient Greeks were already pondering the “plurality of worlds”. They thought that the Earth must be at the centre of everything, and that the Sun, Moon, planets and stars all fitted into concentric spheres which encapsulated the Earth. Disputes arose within different schools of thought for the Greeks: that the universe was made up of an infinite number of particles with repeated interactions and therefore an infinite number of worlds; the Aristotelians believed that the elemental nature of earth and rock was to seek out the centre of the universe, and so how could other worlds exist when Earth is the only planet which can be observed? 

The acceptance of Aristotle’s view eventually proliferated throughout Europe before running into theological problems in the 13th century.

Enter Giordano Bruno in the late 16th century. Bruno pushed the Copernicus model- that the Sun was at the centre of our universe- further than anyone else. He argued that other stars were like our Sun, and so these stars must also have planets, some even with the potential to host life. In 1600 Giordano Bruno was burned at the stake by the Church, mainly for other heretical views not included here, as opposed to his cosmology. 

The multiple-world theory alongside the idea of alien life existing elsewhere captured the attention of many great thinkers in the following centuries. It was not until the mid 1900s that the technology really caught up so these arguments could be placed firmly within the realms of observational astronomy.  

Different techniques were developed to detect exoplanets (discussed in lesson ?.??), and after many failed attempts by other scientists, a team led by Aleksander Wolszczan at Penn State University delivered the first confirmed detection of an exoplanet in 1992 using the radial velocity method of detection. In 1995, a group of Swiss astronomers discovered the first exoplanet circling a Sun-like star, named 51 Pegasi-b. This exoplanet is comparable in size to Jupiter but is orbiting its host star closer than Mercury is to our Sun, and so are called hot Jupiters (imaginative!). These hot Jupiter planets kept popping up as we entered the new millennium, and started to challenge theories of planetary-system formation. But these puzzling finds were about to be complemented by the most prolific planet hunter to date: the Kepler spacecraft. Of the 4000+ exoplanets we now know to exist, the Kepler space telescope has contributed over 2300 of them!