Planets X and Y are perfect spheres that radiate as ideal blackbodies at the same uniform surface temperature. Planet Y has twice the radius of Planet X. During any given 10-minute interval, which statement best describes the total energy emitted by the two planets?
a) Planet Y emits twice as much energy as Planet X.
b) Planet Y emits four times as much energy as Planet X.
c) Both planets emit the same amount of energy.
d) Planet Y emits sixteen times as much energy as Planet X.