One Small Step for a Man, One Giant Explosion for Comet Shoemaker-Levy 9

On April 12, 1961, the apple-cheeked cosmonaut Yuri Gagarin hurtled into orbit and became the first human being to gaze down at the misty blue ball of earth. Tucked into a cute little sphere called Vostok 1, he whipped around the planet only once before tumbling back to earth; in the transcripts of his VHF and short-wave communications with ground control he frequently notes that he's "in good spirits" and doing "very well." Twenty years later to the day, NASA...