But obsolescence can come on several levels, so the Center for Digital Government crafted a definition to truly determine what is — and is not — a legacy system.

Now the International Astronomical Union (IAU) has crafted a new definition for what constitutes a planet that would expand the solar system to Pluto and beyond, encompassing 12 bodies in all.

A working definition lately used by NASA is that "life is a self-sustaining system capable of Darwinian evolution." This definition is often credited to Gerald Joyce of the Scripps Research Institute.