Who were the “visitors” in Solaris?

Question

In the different versions of Solaris (book and three movies), the eponymous sentient ocean planet creates simulacra of persons who were important to the cosmonauts on the space station in orbit.

The main character Kris/Chris Kelvin's simulacrum is his dead wife. The reason Solaris created her as his visitor is, although ultimately inscrutable like everything else it does, at least understandable and explored at length in all versions of the story.

His colleagues' "visitors", as they are called, are however more mysterious and some of them are downright bizarre, both in their appearance and behavior, but also in respect to why Solaris in its alien machinations picked those people to "impersonate".

In the book, Gibarian's visitor is a big, mostly naked, black woman in primitive garb. She has big buttocks and seems to just walk around the station mourning him. In the 2002 film, it's his young son, which is not as weird. In the 1972 film, Gibarian's visitor is instead a teenage girl in negligee who makes Gibarian look like a Professor Humbert:

Sartorius does not appear in the 2002 film, and his replacement Dr. Gordon's visitor is not revealed, to my knowledge. Sartorius's visitor is a dwarf in the book (although it might also be a child there?) and the 1972 film:

Dr. Snaut's visitor is not revealed in the book or 1972 film, I believe, but in the 2002 film (where he is called Dr. Snow) it's eventually revealed that

the Dr. Snow we have met throughout the film is actually the simulacrum, and that he killed the real Snow in self-defense. Why would Solaris conjure a doppelgänger of Snow himself?

I understand that the point of the story is that Solaris is unknowable and impossible to communicate with, but although we don't understand its motives, there are things about its decision to have his dead wife (who committed suicide) visit him that we can understand on a macro level: Solaris poked around in his brain waves, and recreated painful or poignant memories of his in physical form. So:

Who are all these other visitors?

Is it ever explained or implied who these visitors actually are the doppelgängers of? What do they represent?

(Note: I have not seen the first 1968 film.)

Answer 1

I'm taking my info from the book, not the movies. Ultimately you answered your own question by writing: "Solaris is unknowable and impossible to communicate with". Even the scientists are ultimately at a loss to explain things.

Sartorius calls the visitors "Phi-Beings". Kelvin confirms that they are stabilized neutrino fields, unimaginably powerful and complex technology, far beyond anything humanity has seen.

In the last few chapters, Kelvin and Snaut discuss the visitors relation to the ocean. They consider them to be a kind of probe of the base crew. The ocean didn't understand the concept of individuality, so it copied something from what it could perceive. It didn't know what it copying, it just took something that seemed to be in the deepest core of each person.

The readers get examples of this indirectly in the description of the Symetriads and directly in the description of the Mimoids. Mimoids can copy any inorganic object nearby with amazing detail. Symetriads constantly seem to be breaking the known laws of physics and chemistry and biology.

The book has many references of the ocean creating objects that are strangely familiar to the human viewers, yet also completely alien.

In the book, Snaut's visitor wasn't a copy of himself. We don't see Snaut's at all, only the aftermath of his "divorces". We only see a small straw hat from Sartorius' visitor, who seems to be child sized.