Asteroids and Distant Minor Planets: Time Capsules of the Early Solar System

A 12,000-word short read eBook introduction to the Solar System's smaller members. The minor planets are the remnants left over from the formation of the Solar System. As their name implies, they are small. Even the dozen or so largest, some of which are now ranked as 'dwarf planets', are far smaller than the Moon – and these account for a thousandth of one per cent of the total known to astronomers. Most are far smaller. Once dismissed as "vermin of the skies" and "of very little interest to anybody", they are now of great interest. To astronomers and planetary scientists, minor planets offer tantalising clues about the early history of the Solar System. They may be likened to time capsules of the solar system because they preserve material from its earliest stages of formation. Insterest in minor planets extends well beyond that of science. Though we are understandably concerned about the dangers of near-Earth asteroids colliding with our planet, these bodies are also increasingly viewed as a potential source of materials critical for both space exploration and for use here on Earth. Carbonaceous (C-type) asteroids contain water, organics, and volatiles, all of which can be used to support operations in space and reduce dependency on launches from Earth. The minor planets are the remnants left over from the formation of the planets. When the Solar System formed around 4.57 billion years ago, the newborn Sun was surrounded by a rotating protoplanetary disk of gas and dust. Within this disk, microscopic grains gradually accreted into larger planetesimals. The composition of these planetesimals reflected their distance from the Sun: those closer to the Sun were predominantly silicaceous; those further out were carbonaceous, with traces of volatiles; further out still, ices, volatiles, and organics predominated. To astronomers, minor planets offer tantalising clues about the early history of the Solar System. They may be likened to time capsules of the solar system because they preserve material from its earliest stages of formation. Unlike planets, which have undergone extensive melting and geological processing, minor planets have often remained largely unchanged. Their compositions serve as a record of the chemical environment of the protoplanetary disk and the processes that operated within it. The sample return missions have provided pristine asteroid material for laboratory study. The material will give planetary scientists insight into how dust and gas condensed into solid bodies, how those bodies differentiated, how water and other volatiles were delivered to the inner planets, and other critical events in the early history of the Solar System.