That is, it's obvious that Solaris belongs, more strictly than Dick, to the category of philosophy done as science fiction. What if we could reify characters who existed only on our mind? (Not surprisingly the character so reified is named Rhea, a pun I think on reification as well as an allusion to Heraclitus's "panta rei" (πάντα ῥεῖ) - everything flows: Solaris is an ocean planet.) Or put differently, what if we literalized psychoanalytic fantasy, so that memories came alive, transferential relationships become material and actual? It seems obvious that the book is about such psychoanalytic reifications: hence the glimpses into the circus of the repressed fantasy lives of Kelvin's colleagues.
But if we moved from the psychoanalytic to the philosophical we'd be up against the telescoped skepticism that Descartes considers: the outside world may simply be my projection or dream; other people may be my projection or dream. Then I realized that this would make the planet Solaris itself play the role of the genius in Descartes (he calls it evil, but we could see it, as Lem does, as completely inscrutable), the entity that makes us believe in the false or non-existent outside world that we perceive.
Lem's depiction of the planet brings out the psychoanalytical dimension of this philosophical meditation: like the analyst's the planet's inscrutability is at the heart of the transferential relation. And Rhea's state of being is transitional, again in a completely psychoanalytical way. She is at once a part of the inscrutable mind of the planet, with superhuman powers and strengths, and a lonely, confused, unhappy human who has no connection with the sources of her being. Her bewilderment and vulnerability is essential to the love story, to the story of recovered love. Transference onto the planet being impossible (that might be how to describe the twin goals of analytic neutrality: to elicit transference in its most direct form and to make transference impossible), it finds its target in Rhea instead. Of course what's transferred onto Rhea is not, quite, the love of another being, prior to Rhea. It's love of Rhea herself. (That's why it happens twice.) The short circuits of analytic transference are canceled out when it comes to the planet, and intensified when it comes to Rhea.
Cavell too sees Cartesian skepticism from a psychoanalytic perspective: why do we want to disbelieve in the outside world? Because we want to disbelieve in other minds. Why? Because they threaten us, threaten our own sense of psychic integration and self-protection. How do we know this from Descartes? Because this threatening personage is an evil genius. What must we do? Acknowledge Rhea.
This would make Solaris more or less like Merrill's Book of Ephraim. One telling moment is Ephraim's own moment of confusion and clarification, confusion-as-clarification from 1962:
AM I IN YR ROOM SO ARE ALL YR DEAD WHO HAVE NOT GONE INTO OTHER BODIES IT IS EASY TO CALL THEM BRING THEM AS FIRES WITHIN SIGHT OF EACH OTHER ON HILLS U & YR GUESTS THESE TIMES WE SPEAK ARE WITHIN SIGHT OF & ALL CONNECTED TO EACH OTHER DEAD OR ALIVE NOW DO U UNDERSTAND WHAT HEAVEN IS IT IS THE SURROUND OF THE LIVING