Jupiter gives back into space twice the energy it gets from the ...

[james0929]

Jupiter gives back into space twice the energy it gets from the distant Sun. Where is this energy coming from, for the most part?
 
  A) the impact energy of comets like SL-9
  B) helium rain descending into its mantle and core
  C) the slow escape of gravitational energy left from its formation
  D) the radioactive decay of U-238 in its iron-rich core, just as with the Earth
  E) the combined tidal stress of all four large Galilean moons

Question 2

Which classes of stars with large habitable zones probably don't last long enough for life to evolve to use them?
 
  What will be an ideal response?

[amcvicar]

Answer to Question 1

C

Answer to Question 2

Classes O through A are all probably too short-lived for life to get technical.