Wild Space
Wildspace is the empty vacuum between astronomical bodies inside a Crystal Sphere. The boundaries between a planet's air envelope and wildspace were gradual. As altitude increased, air became increasingly thinner until it was considered vacuum. Most crystal spheres did not have an internal atmosphere and were filled with wildspace instead. Crystal spheres appeared to have the property of maintaining the emptiness of wildspace inside them, preventing the Phlogiston from penetrating through any portal that was opened on their surfaces
As an infinite, airless place, Wildspace is populated with clusters of moons, planets, stars, and other objects known as Wildspace systems - serving as the most highly populated locations within this realm. Wildspace is most commonly traversed using interstellar vessels known as Spelljamming Ships, allowing creatures to explore and travel beyond the stars. Within the depths of Wildspace, adventurers can encounter a wide range of creatures and monsters alien to the Earth-like worlds they're home to. These range from fiendish Space Clowns to massive Cosmic Horrors capable of laying siege to entire planets.
Unlike our real vacuum of space, which would cause a creature to immediately perish without the proper attire and breathing mechanisms, Wildspace utilizes a mechanic called Air Envelopes. If a creature enters the vacuum of Wildspace, they form a small bubble of air called an Air Envelope. While this bubble's size is determined by the creature's size, this personal Air Envelope has enough oxygen to support them for one minute before they begin to suffocate. While this means you aren't immediately doomed if you find yourself outside your Spelljamming Ship, you're certainly on a timer before things start to get messy. Uniquely, objects are also home to air envelopes, with the atmosphere of a planet classifying as a massive Air Envelope. Additionally, Spelljamming ships are home to their own Air Envelopes, which can sustain fresh air quality for 120 days before needing to be attended to.
Gravity is interestingly a flexible force of nature within Wildspace. When applied to the likes of planets, moons, and sizable asteroids, the force of gravity functions exactly as you would expect it to, with a radius equal to the object's Air Envelope. This means that massive worlds with enormous Air Envelopes have forces of gravity that require a significant amount of flying to escape, while smaller moons can be left with ease. Additionally, gravity within Wildspace affects ships differently than other objects, as the force of gravity is level and flat, horizontally aligning with the ship's deck. This prevents creatures from walking on the inner and outer walls of a ship.
For those who aren't playing a race like Warforged, which isn't required to breathe, there are a few reliable ways to ensure you're able to survive in Wildspace. First and foremost, perhaps the most reliable means of surviving in the vacuum of space is the recently introduced Air Bubble spell. Available to Artificers, Druids, Rangers, Sorcerers, and Wizards, this spell lasts for 24 hours without requiring concentration, bestowing a creature with a bubble of air that allows them to breathe in airless environments for its duration. For those lacking spells, the new Fish Suit magic item covers your entire body, allowing you to breathe in airless environments. It even provides you with a flying speed equal to your walking speed when within an environment lacking gravity.
Fire burns normally within the air-envelope surrounding a ship. Outside of that envelope, however, is a vacuum that will not support combustion. Magical fire (such as the fireball spell) functions normally in space, since it involves the sudden creation of fire that does not require oxygen or a source of fuel. However, it can not cause other materials to burst into flame.
Divine or priestly magic functions normally in the wildspace of a priests native sphere, but is severely hampered when entering the phlogiston. A priest receives their spells through a connection with their deity, whose efficacy ends at the crystal sphere. Extra-dimensional magic that connects to other planes, whether summoning outerplanar creatures or enabling extra-dimensional travel function normally in wildspace.