The extended scene following Berton as he rides back to the city was filmed in Osaka and Tokyo. Foreign travel was not easily approved, and the reason this long scene was left in the movie was probably to justify that trip for the director and crew.
It is quite common to hear this film compared to 2001: A Space Odyssey (1968), however, Tarkovsky had not seen that film before shooting Solaris. When he did get round to seeing 2001, he criticised it for being "sterile".
In Lem's novel, Hari is spelt "Harey", an anagram of Rheya. This is probably a reference to the titan "Rhea", who was mother of the Gods in Greek mythology, and which is also the name of a moon of Saturn. Rhea was the wife of Cronus/Saturn (the ruler of time), and the sister of Oceanus (Solaris is an ocean planet) and Tethys, a sea goddess, as well as the mother of Poseidon/Neptune; her parents were Uranus (the sky god) and Gaia (the earth goddess).
Snaut mentions the legend of Martin Luther and the inkwell. Luther, who was the founder of the Protestant Reformation, is said to have thrown an inkwell at the Devil to drive him away, when he tried to annoy him in the night. This may, in fact, be a simple misunderstanding. Although there is an ink stain on the wall of Luther's room at the Wartburg, the notion that he had "driven the Devil away with ink", may in fact refer to his German translation of the Bible, and his writings, and so to be taken metaphorically.
There are a number of references to Cervantes' "Don Quixote" in the film. In the library, Snaut quotes from the novel ("Never before, Sancho, have I heard you speak so elegantly as now.") At one point, Dr Snaut also refers to tilting at windmills, and during the weightless scene, an open copy of Don Quixote flies past, showing the knight errant on his steed Rosinante.
A number of sources claimed that Soviet officials withheld the 165-minute version from export. Mosfilm did indeed issue this version for export, and subtitled prints were being shown in the United States in 1973.
While Solaris mostly doesn't concern itself with real-world technology and doesn't refer to it much, it does correctly predict two devices which did in fact become commonplace: home video recording and widescreen flat-panel TVs. Ironically, these are both shown in the pastoral first part of the film.
A print was screened at the Cinema Village theater in New York City in the mid-1980s that combined an English-dubbed version of the film with sequences from a Russian-language print. This version also featured cheesy 1970s-era titles. Around this time, this was considered the most complete version of the film available in the United States. It was not until the re-opening of New York's Film Forum theatre in 1989 that the complete and uncut Russian-language version was shown there theatrically.
In addition to Pieter Bruegel the Elder's "Hunters in the Snow", the painting that is meditated on in the library, three more of his paintings can be seen displayed there during the weightless scene: "Landscape with the Fall of Icarus," "The Harvesters," and "The Gloomy Day, beginning of Spring."
Two characters' names vary a great deal in the different versions of this story. The female character is known as "Rhea" in the novel, "Hari/Khari" in the subtitles and Russian dialogue, "Carrie" in the English dubbing, and "Rheya" in Steven Soderbergh's remake. The Doctor is known as "Snow" in the English translation of the novel and Soderbergh version, "Snaut" in the subtitles and Russian dialogue, and "Stroud/Strowd" in the English dub.
Henri Berton's name may be a reference to André Breton (1896-1966), the leader and founder of the surrealist movement. His last name is an anagram of "Breton", and his first name "Henri" is a French forename.