The adjective of the planet Mars is Martian (note the s changes to a t). This is part of common knowledge, and it is in use in the Expanse novels.
The adjective of the planet Jupiter is Jovian (the exclamation "By Jove!" might be a more known example of this declination quirk). This is nowhere near as commonly known, but nonetheless it is in use in the novels.
The adjective of the planet Venus is Veneral. This is, I would think, more well-known than Jupiter, but nonetheless it is not used in the novels (in particular in the second novel, Caliban's War, where the sun's second planet is more in focus).
Does anyone know the reason that S. A. Corey did it this way?