Understanding Solaria
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 delicacy known as the pachinka.
 Too few people
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. 20,000 years later, the population was 1200—one human per estate.
By the time Elijah Baley visited Solaria around 5022 AD, 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 telepresence "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, and its population was believed to decline by other Spacers. Around 5222 AD, 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 The human inhabitants vanished, giving the impression that they had died out, although they had in fact withdrawn underground; their estates continued to be worked by millions of robots.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 a brief visit, D.G. Baley, R. Daneel Olivaw and Gladia Delmarre barely escaped with their lives.
 Self-dependency for Solarians
During the period from 5,000 AD to 20,000 AD, 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 focused 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.
 The arrival of outsiders
In 499 F.E. (approximately 25,066 AD), 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 (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 accidentally 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 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.
At the end of the book, it was suggested that the Solarians had modified themselves so much that they no longer counted as human, and that their behavior could no longer be predicted by psychohistory, necessitating the creation of Galaxia. Another possible reading[who?] of that passage 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.
The ultimate fate of the Solarians is unknown, although Sarton Bander seemed to believe that Solaria had a bright future.
- Planets: 3
- Position: Solaria III
- Diameter: 15,000 km (9,300 mi), 1.24 that of Earth
- Known locations: Helionia, on the northern continent.