From Sega Retro
The Sega Jupiter is an unreleased console developed by Sega during the early 1990s. The Jupiter would have been a cartridge-based 32-bit console with similar (if not identical) specifications to the Sega Saturn. It is frequently confused with the Sega 32X project, codenamed "Mars".
The concept of the Sega Saturn being able to run cartridge-based (as well as compact disc-based) software was explored during development (and explains the reason for the console having a cartridge slot), but was ultimately scrapped in favour of being disc-only. The Jupiter was rumoured to have been essentially a Saturn without a CD drive, so would have been able to run the same cartridge based software, had any been made. EDGE magazine also suggested that the Jupiter would have retailed for ¥30,000 (at the time, the Saturn's price was set at ¥50,000), and could have been converted into a Saturn by purchasing an extra CD drive (similar to the relationship between the Sega Mega Drive and Sega Mega-CD).
Work is rumoured to have begun in early 1994, though unlike the Sega Neptune, no prototypes of the Jupiter were ever made. By mid-1994 the idea had been scrapped entirely, though the concept was explored again for Sega Titan Video arcade hardware the following year. The Jupiter is said to have been scrapped for the simple reason that CDs were a more cost-effective form of media, and that the industry was moving away from the more limited cartridge format.