Since the beginning of time, humans have looked up at the night sky with a mix of wonder and awe. Flashes of bright light across the darkened heavens inspired fear and dread in ancient cultures. What were these brilliant streaks? Something similar to lightning? Or harbingers of doom? With the invention of telescopes and better observation tools, scientists came to understand these magnificent bursts of light as comets, asteroids and meteoroids, leftover bits of rock and ice from the formation of our solar system.
Woodcut showing destructive influence of a fourth century comet from Stanilaus Lubienietski's 1668 Theatrum Cometicum.
(From “Comets: A Chronological History of Observation, Science, Myth and Folklore” by Don Yeomans. Used with permission.)
About 4.6 billion years ago, at the very beginning of our solar system, a vast disk of dust, gas and ice circled the young Sun. Over thousands of years, this "solar nebula" was pulled together by gravity to form the celestial bodies as we know them today. Some of the small rocky and icy bodies in this disk would come together to build the planets, but billions of these ancient objects remained after the rocky planets and gas giants began to take shape. These small worlds, the remnants of that time long ago, are the asteroids, comets, dwarf planets, and meteoroids of today. They still circle the Sun, reminders of that early, fast and furious time of planet building.
Many of these worlds have been altered very little since they first formed. Their relatively pristine state makes the comets, asteroids and dwarf planets wonderful storytellers with much to share about what conditions were like in the early solar system. It is the tale of our own origins, chronicling the processes and events that led to the birth of our world and the delivery of the water and raw materials that made life possible – from the iron in our blood to the air we breathe.
The purpose of this section is to spotlight these Small Worlds and provide a wide-ranging yet concise view of where they are, how we explore them, and why scientists are so interested in what we can learn from them. After you experience Small Worlds, we hope you will also be intrigued and have many questions of your own.