Bankruptcy?: At no time may your Money Storage Marker move below zero on your Storage Track. You must Trade Materials and/or Science for Money to Pay your Civilization Upkeep Cost or Abandon Control of Sectors until your Civilization Upkeep Cost is small enough to be paid using the Money you have. When a Sector is Abandoned its Influence Disc is returned to the Influence Track (decreasing your Civilization Upkeep Cost), and all Population Cubes from the Sector are returned to their respective Population Tracks (Population Cubes from gray Population Squares may be returned to any Population Track and Population Cubes from Orbitals may be returned to either the Science or Money Population Track; if a Population Cube needs to be returned to a Population Track that is full, place the Population Cube on another Population Track of your choice.)
Note that Abandoning Sectors may cause Population Cubes on Money Population Squares to return to the Money Population Track, reducing Income (and the ability of Abandoning Sectors to keep your civilization solvent).