The most that scientists knew about Mercury, Venus, or Jupiter was their size, surface temperature, and atmospheric composition. But on Dec. 14, 1962, the Mariner 2 spacecraft flew by Venus. For the first time, researchers had detailed and up-close information about another world, helping spawn new scientific fields such as astrogeology and modern planetary science. The planets in our solar system changed from distant points to fully fledged worlds, with distinctive and amazing features.