Many of the primitive bodies wandering the asteroid belt between Mars and Jupiter are former comets, tossed out of orbit by a brutal ballet between the giant outer planets, say a team of astrophysicists. A commonly accepted theory is that the asteroid belt is the rubble left over from a...

The US National Ignition Facility is designed to demonstrate the feasibility of nuclear fusion, a process that could offer abundant clean energy. The lab will kick-start the reaction by focusing 192 giant laser beams on a tiny pellet of hydrogen fuel. To work, it must show that more energy...