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How did small bodies preserve evidence from the planet-building process?
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Small body
Asteroid Ida and its satellite, Dactyl, photographed by the Galileo spacecraft on August 28, 1993, from a distance of about 10,870 km (6,750 miles). Ida is about 56 km (35 miles) long and shows the irregular shape and impact craters characteristic of many asteroids. The Galileo image revealed that Ida is accompanied by a tiny companion about 1.5 km (1 mile) wide, the first proof that some asteroids have natural satellites.
Small bodies, such as asteroids and comets, serve as vital time capsules from the early solar system because they are remnants of the intermediate stages of the planet-building process. They preserve evidence of these ancient events primarily for two reasons:12
- Early Formation: These objects are leftovers from the initial aggregation of dust and grains into larger bodies. Unlike the planets, which grew into massive, complex structures, these small bodies were never incorporated into larger planets or captured as satellites, meaning they remain representative of the material present during the solar system's infancy.12
- Thermal Preservation: During the formation of the solar system, larger bodies experienced significant heating due to the decay of radioactive isotopes and frequent collisions, leading to extensive melting and chemical differentiation. In contrast, small bodies were able to radiate this heat away efficiently, keeping their interiors relatively cool. This allowed them to preserve the original dust and primitive material from which they formed, with some meteorites even containing material that predates the solar system itself.1