The Sun is a natural nuke - still going off.
http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor
Do a google on “critical mass”.....the earth nor any other planet in our solar system do not have it.
Nope, not even Jupiter despite Arthur C Clark.
The Sun is 1.3 MILLION times larger by volume than the Earth.
That’s why its a star.
;-)
Cheers!