Solaria was a fictional human-inhabited planet in Isaac Asimovs Foundation and Robot series. It features mainly in The Naked Sun, to a lesser extent in some later novels. Solaria was the last of fifty Spacer worlds colonized by humans in the first wave of interstellar settlement, occupied from approximately 4270 AD by inhabitants of the neighboring world Nexon originally for summer homes. It was ruled by a Regent after it became independent around roughly 4500 AD. The Solarians specialized in the construction of robots, which they exported to the other Spacer Worlds. Solarian robots were noted for their variety and excellence. They also exported their grain, which was used to make a pastry known as the pachinka. Ultimately, Solaria became totally dependent on robot labor; roughly 10,000 robots existed for every human. The world was extremely sparsely inhabited, with only 20,000 humans (and 200 million robots) inhabiting 30 million miles² (78 million km²) of fertile land, divided into over 10,000 huge estates (the exact number is unknown, since some of the estates were inhabited by couples). The population was kept stable through strict birth and immigration controls. In the era of Robots and Empire, no more than five thousand Solarians were known to remain. 20,000 years later, the population was 1200—one human per estate.