It was the last of the fifty worlds to be colonised by the Spacers, settled in approximately 4720 A.D. by inhabitants of the neighboring world Nexon originally for summer homes. It was ruled by a Regent after it became independent around roughly 4500 A.D. The Solarians specialised 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 delicacy known as the pachinka.
Ultimately, Solaria became totally dependent on robot labour; 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 (77,666,430 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. 20,000 years later, the population was 1200—one human per estate.
By the time Elijah Baley visited Solaria around 5022 A.D., its inhabitants had evolved an isolationist culture in which its citizens never had to meet, save for sexual contact for reproductive purposes. All other contact was accomplished by sophisticated holographic viewing systems, with most Solarians exhibiting a strong phobia towards actual contact, or even being in the same room as another human. All work was done by robots.
Over the following centuries and millennia, Solaria became even more rigidly and obsessively isolationist. Around 5222 A.D., Solaria cut off all contact with the rest of the Galaxy (although continuing to monitor hyperspatial communications). The human inhabitants vanished, giving the impression that they had died out, although they had in fact withdrawn underground; their estates continued to be worked by millions of robots. It was eventually forgotten entirely as the other Spacers died out, with any stray visitors to the planet being attacked and killed by robots programmed to view non-Solarians as non-human. During this time, the Solarians had extensively modified themselves through genetic engineering to become hermaphrodites, thereby removing the need for sexual contact. In a more important development, Solarians evolved (or engineered) small transducer lobes, a section of the brain about the size of a hen's egg, protruding behind the ears. These were able to collect any free energy from spontaneous heat flow in their surroundings, on the principle of a heat engine, and direct this extracted energy into focussed useful work, at a distance, by thought. Using these lobes, Solarians manipulated their environment with powers akin to telekinesis, and provided for the energy needs of their entire estates, including power for all of the estate's robots, drawing energy from the various spontaneous thermal energy transfers of the planet in apparently complete compliance with the known laws of thermodynamics. Solarian estates commonly featured conductive rods, spaced at convenient distances, penetrating deeply into the planet that, at a touch, made the channeling of geothermal energy between the planet's interior and the heatsink of space even easier.
In 499 F.E. (approximately 25,066 A.D.), as told in the novel Foundation and Earth, Solaria was visited by Golan Trevize, Janov Pelorat and Blissenobiarella. They landed on the estate of Sarton Bander, the "Ruler" of a Solarian estate. They learned of the sociological developments of Solaria through Bander, who apparently took a secret pleasure in having 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 his shameful personal contact with offworlders, Bander attempted to kill the visitors, but he was killed instead by Bliss, resulting in the shutdown of all of the robots and other machinery of Bander's estate. The visitors were able to escape, but not before discovering on the estate a child, 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 for him at the appropriate time), who they would ultimately bring with them to Earth. The child would stay on the moon to mentally merge with Daneel Olivaw. At the end of the book, it was suggested that the Solarians had modified themselves so much that they no longer counted as human, to the point that their behaviour could no longer be predicted by psychohistory. Another possible reading of that passage was that the Solarians had become, in essence, aliens. Yet another alternative is that Fallom appeared to be Solarian but had been planted at the estate, in a manner similar to the impostor, Sura Novi, that Gaia had inserted into the Second Foundation in the preceding novel.