On Dec. 5 at 1 o'clock in the morning local time, researchers at the Lawrence Livermore National Laboratory in California used lasers to zap a tiny pellet of hydrogen fuel. The lasers hit their target with 2.05 megajoules of energy, and the pellet released roughly 3.15 megajoules. It's a major milestone, and one that the field of fusion science has struggled to reach for more than half a century: producing a fusion reaction that generates more energy than it consumes. While progress, the technology is still a ways off from its promise to produce energy without creating greenhouse gases. Today on the show, Regina G. Barber brings us two NPR stories that explain what this experiment showed and what else needs to happen to make fusion a practical energy source.