There are a whopping three planets in the habitable zone, all of which are inhabited to one extent or another. There is Ashyn, the burning planet, which suffered a cataclysm long ago. People here live in very small pockets of survivability, including the famous floating cities. Farthest out of the three is Braize, which despite being cold and inhospitable to men is home to an ecosystem of self-aware Splinters. (The local parlance would call them spren.) I believe it’s possible some of these are actually Cognitive Shadows, but research here is difficult and dangerous, so I will hold back on theorizing for the moment.

The showpiece of the system is, of course, the middle planet of Roshar itself. At 0.7 cosmere standard in gravitation and 0.9 in size—and possessing a high-oxygen environment—Roshar is home to a diverse and unique ecology containing dramatic megafauna and fascinating symbiotic relationships between creatures (both humanoid and not) and Splinters of Investiture.

The most dramatic of these is the relationship between humans and self-aware spren, which is the basis for the magic of Surgebinding. This magic has strong roots in natural physics, with the spren being personifications of the forces themselves (called Surges locally). Gravitation, the strong axial force, surface tension … these things have come alive, as have more abstract notions such as transformation and transportation.

However, this pattern (the bonding of spren to human) is merely an expansion of what already exists in the nature of the planet. Gargantuan crustaceans grow to incredible size without collapsing under their own weight not just through the nature of the planet, but through symbiosis with spren. Certain animals obtain flight through similar means, and there is even a race of equines that—through the spren bond—have adapted to life on the planet and obtained a high enough level of self-awareness to nearly be named a sapient species.

I will not speak on the relationship of Roshar’s divergent ecology here, as that is a topic too large to address in a simple survey such as this one. However, travelers to the planet should be made aware of the storms. Life on Roshar has been shaped over millennia by massive, Invested storms, which pose a danger that cannot be overstated.

These storms, by my best guess, predate the arrival of the Shards Honor and Cultivation—as do many of the spren. However, the presence of the Shards molded and transformed the planet’s nature to the point that it is difficult to distinguish what is pre-Shattering in origin, and what is a newer development. Surely, many of the spren that now exist on the planet have arisen from the friction between Honor, Cultivation, and Odium.

Odium. Be aware that this system is the current habitation of the Shard of Odium on the Physical and Cognitive Realms. This Shard undoubtedly caused the Splintering of Devotion, Dominion, Honor, and perhaps others throughout the cosmere.