Men from the Sea

"Men from the sea
Might rise" -Lucretius

And they do, at least on the planet Solaris.
Each of the scientists has a visitor which is a product of their subconscious turned flesh and blood by the ocean's primordial power.

The hero Kelvin is subject to his deceased lover; the god Rheya is also his muse. The manner in which she adulates Kelvin creates her not as a separate entity but rather entwined wholly with him. Wherever he goes, she follows, so much so that she cannot stand to let him out of her sight. Likewise Kelvin unconsciously needs Rheya.
"And my hand lingered, moved up her warm, rounded arm. In spite of myself I was caressing her. My body recognized her body; my body desired her, my body was attracted towards hers beyond reason, beyond thought, beyond fear."
 All rationale is secondary to this desire and necessity for a lover, for a god. Rheya is not a separate entity but principally a byproduct of Kelvin's mind and secondly as a corporeal manifestation of this need. Even his body is moved "beyond reason, beyond thought" to have her as his muse, as his god, disavowing self-preservation, scientific fundamentals, and all concept of reality.
"We have no need for other worlds. We want mirrors."
As Snow states, the need for other is unnecessary. All that mankind wants in the exploration of new frontiers are "mirrors" with which to reflect himself. The god is a part of the man and his quest seeks affirmation that this god is both unrivaled and unique.

There is only one other visitor which is revealed to readers in the novel; the tall, muscular, black "Negress." Kelvin finds her huge form coiled up against the dead body of Gibarian. Somehow this god figure born of Gibarian's psyche had driven him mad enough to commit suicide and, like Kelvin, was unable to detach himself from her even in death.

Snow's visitor is left purposefully ambiguous. The movie, however, does insert a child into the narrative which is purportedly his dead son.

So how to merge the comparisons of Lucretius and Solaris into a unified project...