It depends if we're talking Solaris the movie or the Solaris the book. The book makes it clear that the ocean is reading the minds of the space ship inhabitants

It depends if we're talking Solaris the movie or the Solaris the book. The book makes it clear that the ocean is reading the minds of the space ship inhabitants somehow and attempting communications with them by recreating familiar objects through neutrinos that they can somehow physically interact with. Subsequently the book is all about an attempt to establish communication with the ocean while at the same time enduring its phantoms, with the end result being that humans are unable to decipher the intentions of the ocean or communicate with it in any way. Expanse is more along the lines of "geopolitics in space" with the protomolecule being a MacGuffin to drive the plot along and create space zombies and wormholes. Which isn't to be derisive, as I find it very entertaining, but I don't feel like it's delving deep into the scientific or philosophical ramifications of first contact.