Asteroids, Comets and Our Cosmic Landscape
To understand the overall scale and distances of our planetary system and all its inhabitants, including the planets, asteroids and comets, we must first get a little background. The early solar nebula, the great cloud of dust and gas from which all planets and moons and other objects came, originally lacked any big planets. The Solar System began as a great cloud of interstellar gas, much like many of the beautiful nebulae we see today (see Chap. 6). Those nebulae provided clues to early theorists about how our Solar System came together. Among them, Swedish scientist Emmanuel Swedenborg proposed a simple “nebular hypothesis” in 1734. His theory described a hot globe of material around the infant Sun as the birthplace of the Solar System. German philosopher Immanuel Kant (1755) later enhanced his theories. French astronomer Pierre-Simon Laplace (1796) added even more detail, suggesting that the primordial cloud surrounding the Sun somehow flattened into a disk, eventually leading to the genesis of the planetary system.