Tumblr user fantrorillaz asks, “How does interplanar travel intersect with interplanetary travel? Does every planet have its own planes or does the universe each share its own planar cosmology? If you’re suffocating in space would it be viable to Gate yourself to the elemental plane of air? Is there such thing as a feywild or shadowfell in space?”
What a wonderful question! The Core Sourcebook has a whole section about this in Chapter One, but I’ll lay out some brief details here.
Some planes exist overlaid across the entire universe and others are unique to each individual planet. The Elemental planes and what most would call the “Divine” planes both overlay across everything. That means you can totally gate yourself to the Plane of Air if you get sucked into open space (assuming you survive the vacuum, cold, and radiation). The Ethereal and Astral planes likewise touch everything.
On the other side of this, there are a few planes that only touch planets or only touch the void of space. There are a nasty realm of outer planes that only touch space and are filled with Abominations and Aberrations. Lots of bad stuff comes in from there.
The planes of the Fae Beyond and the Nightveil are unique to each individual planet. Every world with life on it has its own version of these two, but they are like mirror worlds and often have distance portals and connections to each other. So if you anger a faerie queen connected to one planet and then go into the Fae Beyond of another, there might be an echo of that emotion, but you won’t be facing down the same queen.
For all the juicy details you’ll have to pick up the Core Sourcebook tomorrow and read all about it!