One of the most oft repeated bits of trivia about Solaris is that the source book's author, Stanislaw Lem, decried Tarkovsky's adaptation on the basis that he didn't write about, "...people's erotic problems in space." This quote, particularly when taken in the context of Tarkovsky's later comments on 2001: A Space Odyssey, (he considered it "sterile") suggest the film be read as just that: a treatise on peoples' erotic problems in space. And, having not read Lem's novel, for all I know it might be when judged in comparison to its predecessor. But on its own terms Solaris own presents itself as something rather different: a film about the difficult relationship between humankind's tendency to navel-gaze and its ability to engage with the universe around it.
In Solaris' beginning it is the scientific questions which are brought to the fore. While human loss hangs over the proceedings - brooding walks, recurrent references to the day's personal meaning, even a portrait - the text remains stubbornly devoted to the questions of Solaristics. Men sit around and debate whether there remains any scientific value left in the project and how one measures the worth of scientific knowledge. Perhaps most tellingly of all the early scenes end with the remarkably alienating, humanity-defying traffic sequence.
It's only when Kris actually reaches the station that "erotic problems" begin to surface. But this apparent change in focus simply dovetails with the film's own thematic concern: namely the difficulty humans have approaching matters with import beyond their existence and that imply limits to their existence. It's a concern which is hinted at in Dr Snaut's suggestion of acclimatisation through placing cut-up paper in the air vents to mimic the rustle of leaves on Earth, and which is latter brought home more forcefully in his birthday speech in which he insists that humans don't want to discover aliens so much as they want to rediscover themselves.
Kris is too caught up in worrying about what the reappearance of his dead wife means for him to consider it as part of the larger question of what Solaris is and how (or indeed if) it thinks. Even Dr Sartorius, who forcefully attempts to ignore any human dimension to the problem responds to the planet's physical manifestations as an attack on his psyche and responds in kind. As a result of these stubbornly human respones Solaris' interaction with the people on the station becomes ever more defined by them. As Doctor Snaut and Hari observe: S\she becomes more human the longer she stays around them.
It's no surprise then that the final, almost last ditch attempt to communicate with Solaris consists of the people aboard the space station telling the planet who they are. It's even less of a surprise that the apparent "breakthrough" appearance of islands on the surface of Solaris is merely yet another case of the planet being made to reflect themselves.