Mimas, at the upper right, has an enormous impact crater on one side, and Tethys, at the bottom, has a huge rift zone called Ithaca Chasma that runs nearly three-quarters of the way around the moon.

At the bottom of the VFS are the file system abstractions that define how the upper-layer functions are implemented.

"Being well above the bottom is a source of satisfaction, " the CBO report concludes. "But when those at the upper end of the distribution fare better than (you) do, it is a source of consternation."