Inhabited by Spacer descendants, Solaria is the fiftieth and last Spacer world settled in the first wave of interstellar settlement. It was occupied from approximately 4627 AD by inhabitants of the neighboring world Nexon, originally for summer homes. It was ruled by a Regent after it became independent around roughly 4727 AD. It had perhaps the most eccentric culture of all of them. 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.
Originally, there were about 20,000 people living in vast estates individually or as married couples. There were thousands of robots for every Solarian. Almost all of the work and manufacturing was conducted by robots. 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. Twenty thousand years later, the population was twelve hundred, with just one human per estate.
Solarians hated physical contact with others and only communicated with each other via holograms. A few hundred years after Elijah Baley's visit to the planet, Solarians retreated from the Galactic scene and fled underground. The Solarians genetically altered themselves to be hermaphroditic and have the ability to use telekinesis. They specially made robots that were made to kill any foreigners who came to the planet.
In 499 F.E. (approximately 25,066 AD), Solaria was visited by Golan Trevize, Janov Pelorat, and Blissenobiarella. They landed on the estate of Sarton Bander, the "Ruler" of a Solarian estate (note that Sarton was the last name of R. Daneel Olivaw's designer, Roj Nemennuh Sarton of Aurora). They learned of the sociological developments of Solaria through Bander, who apparently took a secret pleasure in having something close to intellectual companionship, or at least an intellectual audience. To prevent them from providing information to the Galaxy about Solaria and in keeping with Solarian customs and beliefs, not to mention preventing other Solarians' discovery of shameful personal contact with offworlders, Bander attempted to kill the visitors, but was instead killed in self-defense by Bliss, resulting in the shutdown of all of the robots and other machinery of the Bander Estate.
The visitors were able to escape, but not before discovering a child in one of the countless rooms of the estate, Fallom, assuming it to be a successor to Bander (who had not mentioned the existence of an heir, but had mentioned that there would be one at the appropriate time or in the case of an unforeseen accident), whom they would ultimately bring with them to Earth. Had they left Fallom on Solaria, the child would almost certainly have been killed, because it was seen as a surplus child and also had not as yet developed its transducer lobes, therefore not counting as a Solarian and being expendable. Fallom demonstrated great precocity in learning Galactic and would eventually stay on the Moon of Earth to mentally merge with Daneel Olivaw.