A Jupiter Brain in the Ain Soph Aur system, silhouetted against the central Dyson swarm surrounding Delta Capricornii
A Jupiter brain is a computational substrate comparable in mass and size to a gas giant planet, typically in the 1X1027 kilogram range.
The computronium basis of a modern Jupiter Brain usually consists of a colloidal structure of plasma, monopolium/magmatter, and/or diamondoid/feroid. Heat dissipation is often a major concern with Jupiter Brains; the denser they are, the faster they can run, due to the distances involved in transmitting internal data. But increasing the density of the computronium also increases the problems associated with the heat of operation.
A Jupiter Brain can be considered to be an AI, posthuman or Local Archailect Node of extremely high computational power and size. This is the typical megascale concentrated intelligence. Such complexity is often considered to be the bare minimum housing for an archailect at the full S4 rating.
The term originated from an idea by early Information Age transhumanist Keith Henson that nanomachines could be used to turn the mass of Jupiter into computers running an upgraded version of himself.