Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Distant
Distant: That's Lem's attitude towards his novel. It sometimes seems like he's writing from the other room, with a blindfold over his eyes and humming loudly so you can tell he's not involved. Yep, the book is over here, and I, your author, am over there. It is going to chug along without me, so don't bother me, reader. And a lot of times, the distance even feels clinical. This can be literal, as in the conversation in which we learn that Gibarian, Kelvin's old friend, has killed himself.
"The locker? Was he dead?"
"His heart was still beating, but he had stopped breathing."
"Did you try resuscitation?"
"No."
"Why not?" (3.57-61)
They might as well be talking about the Solaris weather as about the death of Kelvin's mentor, right? Maybe Kelvin's upset, but even though he's the narrator, Lem doesn't let us get into it; he ain't here for the feelings.
In part, this clinical distance is part of the book's work as parody: Lem's making fun of science fiction's pretense to science. You want cold science? he seems to say. Here are two cold fish talking about a dead body. Have fun!
The parody is also a form of distance, though—and it expresses itself in a kind of abstracted playfulness. The novel is filled with puzzles, which Lem drops in and then never explains. One of these is discussed over in the "Symbolism, Imagery, Allegory" section—Kelvin finds a bunch of tools fused and melted, but we never find out how that happened or why.
Similarly, we don't see most of the visitors. Sartorius's seems to have a straw hat… and why does Snow have bloody hands in that one scene? Why is Gibarian's visitor a semi-nude black woman? For that matter, why do the visitors come and why do they leave? Lem sets up questions and then just abandons the answers, as if they have nothing to do with him.
This distant tone fits with many of the themes of the book. The novel is about how contact is impossible and you can never know the other, and so it treats the text as well as something you can't know. If you can't reach the mind of Solaris, why should you be able to reach the mind of Lem?
When Kelvin thinks, "I did not believe that it could respond to the tragedy of two human beings. Yet its activities did have a purpose" (14.69), he could be thinking of his own author: remote, apparently unfeeling, and yet, somehow purposeful and perhaps even caring—if only from far away.