SHOCK DIAMONDS: Recently, NASA engineers tested a revolutionary methane-powered rocket engine. A blue flame blasted across the Mojave desert, heralding a new kind of spacecraft that one day might roam the outer solar system, gathering fuel from planets and moons it visits: full story.

Many readers who've seen the movie want to know, what are those white shapes in the exhaust?

Answer: Shock diamonds. Also known as Mach disks, they are interference patterns formed by shock waves propagating down the engine's exhaust plume. Shock diamonds are formed when exhaust exits a nozzle supersonically and at a pressure different than that of the ambient atmosphere. The most famous photo of shock diamonds shows Chuck Yeager's X-1 rocket plane just moments after he first reached Mach 1 on Oct. 14, 1947.