The movies often depict the asteroid belt as a danger zone. Space rocks large and small are always just ahead, ready to smash intruding spaceships. Fortunately, the reality is much calmer. More than a dozen spacecraft have flown into or through the belt, all with no problems — and another is scheduled to head that way early next month. The first craft to enter the belt did so 50 years ago today. Pioneer 10 was headed for Jupiter, the solar system’s largest planet. But it had to transit the asteroid belt to get there. The belt is a wide zone between Mars and Jupiter. It contains countless chunks of ice and rock. The largest is about 600 miles in diameter, while the smallest are the size of grains of sand. Astronomers have cataloged more than a million members. In 1972, though, the number of confirmed asteroids was only in the hundreds, so no one knew what to expect. Most thought Pioneer would get a few small dings, but no big whacks. And in fact, it didn’t even get that many dings. It r
