An exploration of “the small space objects such as the comets and asteroids that orbit the Sun.” Popular cosmology books usually focus on stars, the sun, and planets, giving short shrift to everything in between. In an expert account, Starkey, a British geologist and space scientist who lives in California, argues that particles, rocks, asteroids, and comets deserve more attention. The Earth has changed a great deal since the birth of the solar system over 4 billion years ago, but cosmic dust from the birth is still out there along with larger bodies. Comets and asteroids have their own histories, and some dust has existed since near the beginning of the universe, so studying them “means we can understand how our planets were put together and what they contain.” Readers will pay close attention when the author asks a significant question: Where did Earth acquire water and the carbon-containing organic compounds essential for life? She reminds us that scientists believe that planets formed from clumping dust grains that swirled around a hot central mass that became the sun. Pummeled by a rain of other small bodies (planetesimals) and heated by volcanism, the early Earth was too hot for water to condense and complex organic chemicals to form. Only beyond the orbit of Mars were temperatures low enough for volatiles (water, methane, ammonia) to solidify into lighter planetesimals, comets, which often migrated inward and fell upon Earth. Readers familiar with NASA’s robots’ landing on Mars and missions to the outer planets may be surprised at Starkey’s later chapters, which describe probes sent to comets that landed and scooped up samples to return to Earth to educate (and confuse) researchers. A successful introduction to the hitherto neglected bits and pieces of our solar system.