<p> A program calling itself “The Universe” has lots of space to travelnot to mention billions of years to traverse. The History Channel's “The Universe: The Complete Season Six” (out May 15 on Blu-ray and DVD) is comprised of over 10 hours of informed speculation by astrophysicists and others, set to kinetic videogame style visuals with plenty of explosions in the depths of space and the usual stentorian cable documentary pronouncements: “No planet has provided sanctuary from the solar system's reign of terror.” </p> <p>Well, OK, this is science packaged to entertain, but it's science nevertheless, buttressed by talking heads from NASA and elsewhere. And yes, the picture they paint is of a catastrophic universe where worlds have collidednot once or twice but over and over. The peculiar composition of Mercury, whose iron core constitutes 80 percent of its mass? A giant asteroid struck the little planet billions of years back, scattering most of its crust into space (and showering neighboring worlds with debris, including Earth). The serene rings of Saturn? They must have resulted from a shattered moon. </p> <p>The producers of “The Universe” are intellectually honest, admitting that much of this isn't (and can't be) settled science but remains a matter of debate among astrophysicists. Still, the concepts are fascinating and unsettling. What's to prevent a huge piece of rock from wandering off its orbit and striking the Earth with catastrophic impact? It's happened before and could happen again. </p>
