Unconfirmed until 1992, extrasolar planets had long been a subject of
discussion and speculation. In the sixteenth century the Italian
philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by their own planets. In the eighteenth century the same possibility was mentioned by Isaac Newton in the "General Scholium" that concludes his Principia.
Making a comparison to the Sun's planets, he wrote "And if the fixed
stars are the centers of similar systems, they will all be constructed
according to a similar design and subject to the dominion of One."