1961? This book was written in 1961? When British sci fi was dominated by the likes of Arthur C Clarke and Fireball XL5? When Hollywood was still churning out cheap genre flicks like The Blob? Really, it's unbelievable.
I'm relatively new to the field and haven't got my sub genres sorted, but Solaris, to me, is hard sci fi, as hard as it comes. It's not all about technology but the real science - the literature of science - is there. Indeed, it is all about a specific field of science, Solarist studies. Albeit the novel only lasts 200 pages, a good third is devoted to reviewing the literature, from the first explorers to theorists and dissenters. Over a century after its discovery Solaris remains on the cutting edge of astronomical science, with its twin moons, one blue, one red, and its all encompassing 'sea'. Many scientists believe there is life o Solaris. To be precise, they believe there is a single life form, that the sea itself is conscious. The sea amuses itself by creating and then destroying elaborate structures. A permanent space station has been established to observe the process - but the sea is equally studying the observers.
There are only four scientists aboard the station at any one time. Kelvin arrives to find that one of them, his former tutor Gibarian, has died. The other two, Snow and Sartorius, are not exactly welcoming. Snow initially seems to think he's not real and Sartorius has locked himself in his laboratory. Then Kelvin encounters a giant, half-naked, African woman who completely ignores him. This, it turns out, was the 'ghost' that haunted Gibarian. We never find out who or what is haunting Snow and Sartorius, but Kelvin is soon joined by his wife Rheya, who has been dead for the last decade.
What the sea is doing is searching the minds of the humans and creating something that looks like the person of their dreams. These creations have to improve on the likeness, learning from their partner how to behave. Kelvin knows this isn't Rheya - he shot the first clone off into space from which she simply cannot return - yet as the second version becomes more lifelike he cannot help falling in love with her.
Thus, in addition to the deep scientific background, we have a moral and philosophical debate - essentially the sex robot debate over half a century before such things became remotely possible. The twist is that, in the end, even Rheya herself knows she isn't real.
Truly stunning - a breathtaking achievement. The benchmark of thoughtful science fiction.