by: Ursula K. Le Guin
On the planet Winter, there is no gender. The Gethenians can become male or female during each mating cycle, and this is something that other cultures find incomprehensible.
The Ekumen of Known Worlds has sent an ethnologist to study the inhabitants of this forbidding, ice-bound world. At first he finds his subjects difficult and off-putting, with their elaborate social systems and alien minds. But in the course of a long journey across the ice he reaches an understanding with one of the Gethenians - it might even be a kind of love...
Le Guin's story touched upon, in my opinion, some of the most important issues in astrobiology. The climate on the alien world differs from our own, but it is still habitable. A planet that gets its energy from the star it orbits must fall within a certain range to be habitable. Solar systems are light years apart, and travel between them is a slow process. There is also the possibility that there are habitable worlds that don't have life on them. Finally, there is the important issue of how a different environment can cause a major evolutionary change.
Genly Ai, the envoy visiting the planet Winter, explained to the aliens the differences between the various worlds supporting life. The Gethenian world was much colder than the one he came from, but it was still habitable. The search for habitable planets is very important in Astrobiology. One of the prerequisites for surface habitability is liquid water. Why is there water on our planet, but not on any of the others? The answer to that question involves our distance to the Sun. A planet that is too close to the sun can't have water, because the high temperature would result in all the water evaporation. Likewise, a planet that is too far away from the sun wouldn't have water, since it would freeze in the cold climate. We call region of space where water can exist in liquid form the habitable zone. The actual range of the habitable zone is still under question. We know that Venus is too close to the sun, so any water on the surface evaporates into the atmosphere. There is water on Earth, meaning that the inner region must lie between those two worlds. The real question is the location of the outer region. Mars does not have liquid water on its surface. If Mars was a larger and had more of an atmosphere, there is a good chance that liquid water could exist on the surface. Since it isn't, scientists are unsure where to place the outer boundary of the habitable zone. Either way, we still have a good idea of where to focus our attention when we explore other galaxies.
83 planets contained a form of humanoid life in this book. Among those, the closest to the planet Winter is almost 17 light years away. This is very accurate in real life. Earth is the only object in our solar system that contains life (that we know of). The closest star to us is 4.22 light years away. For us to reach this star, it will take several hundred-thousand years. There could be many planets that have intelligent life in the galaxy, but they are too far away for us to reach at this point. Space travel needs to advance to a point where we are able to travel at greater speeds if we are to ever really explore the galaxy.
Genly Ai noted that the Gethenians were very similar to the humans from his world. They had the same system government, social stratification, and cultural divisions that you can find here on Earth. The biggest biological difference between Gethenians and us is their lack of defined gender. For some reason, the beings on this world evolved into a species which did not have any need for gender roles. This difference between us and the alien beings demonstrates the concept of evolutionary adoption. Evolutionary adoption states that an organism will develop traits to help it survive in the surrounding environment. In the case of this book, the colder climates probably increased the difficulty of interaction. To ensure that they would survive, the Gethenians evolved in a way that allowed any human to bear children. If we ever find a world that has life on it, we can expect the creatures to be very different than the ones we are accustomed to.