Oct. 4, 2007 marks the 50th anniversary of Russia's launch of Sputnik, the first artificial satellite to orbit Earth. The "traveling companion's" legacy was far-reaching. Sputnik ignited a dangerous game of one-upmanship between the world's two superpowers, spurred the development of technology capable of placing humans on the moon, and it heralded a new age of discovery that would take humans, or at least their robotic emissaries, to the farthest reaches of the solar system. SPACE.com explores the follow-on effects Sputnik has had on science. - Ker Than