Character Clues
Character Analysis
Actions
We know about Kelvin from his actions… or rather, mostly from his inaction, because in general, he doesn't do squat. There are pages of him sitting in the library reading dry accounts of Solaris rather than trying to deal with, what are, after all, fairly serious problems.
"Apathy robbed me of the strength even to despise myself" (10.124), he thinks, musing about how he's doing nothing… while doing nothing. Or in his relationship with Rheya, he keeps thinking he should try to comfort her or help her, but, pffft: "I wanted to get up, take her in my arms and stroke her hair. I did not move" (12.38). Kris Kelvin, ladies and gentlemen: the hero as limp puddle.
Type of Being
One of the most important means of characterization in Solaris is through the visitors. The visitors come from inside the characters' heads; therefore, in some real sense, the visitors are the characters. Kelvin is Rheya; Snow is whatever his visitor is; Sartorius is his weird little person with the straw hat.
Sometimes this characterization is illuminating: Kelvin's grief over Rheya is the most important thing about him. Sometimes, though, it's just confusing. What are we supposed to make of the brief glimpses of Sartorius's visitor, for instance? Even the confusion is important though. The visitors, after all, come from the ocean—and much of the book is devoted to talking about how we don't and can't understand the ocean. So if the ocean is the visitors and the visitors are the characters, that means that we can't know them either.
The characterization in Solaris is in part about how people are unknowable. As Kelvin says after examining Rheya's blood, "[…] the final step, into the heart of the matter, had taken me nowhere" (7.137). Rheya is a type of being you can't see into—a person as a blank. (If you haven't read her analysis in the "Characters" section, now just might be a good time to.)
Direct Characterization
Solaris uses a certain amount of direct characterization, especially for minor characters. For instance, Snow explains: "Sartorius is trying to remain normal—that is, to preserve his respectability as an envoy on an official mission" (6.141). Later, Snow calls Sartorius a "Faust in reverse" (13.29), suggesting he's a mad scientist, or the opposite of a mad scientist (an overly sane scientist?).
These descriptions make Sartorius seem officious and determinedly respectable and normal. But since they come from Snow, and Snow isn't necessarily the most reliable witness, it's hard to know how to take them. So do we know what Sartorius is like? In this sense, the direct characterization becomes—like "Type of Being"—a way to characterize without characterizing, or to suggest that we don't actually know this person.