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What are Small Worlds?
Poster showing the differences between dwarf planets, comets, asteroids, meteors and meteorites.
What's the difference between once space rock and another? (Click to enlarge.) Credit: NASA/JPL-Caltech

Keys to the Past

The small worlds of our solar system - asteroids, comets, dwarf planets and even meteors - may conceal answers to some of the most fundamental questions about our own origins. How did our sun's family of planets, moons and small bodies originally form? How did our solar system evolve into the diverse collection of worlds we see today? How did life begin on Earth, and could the same processes have caused life to form on other celestial bodies?

At the very beginning of our solar system, before there was an Earth, Jupiter or Pluto, a massive swirling cloud of dust and gas circled the young sun. The dust particles in this disk collided with each other and formed into larger bits of rock. This process continued until they reached the size of boulders. Eventually this process of accretion formed the planets.

Billions of small space rocks never fully evolved. Amazingly, many of these mysterious worlds have been altered very little in the 4.6 billion years since they first formed. Their relatively pristine state makes comets, asteroids and dwarf planets windows to the past- revealing what conditions were like billions of years ago in the early solar system. They can reveal secrets about our own origins, chronicling the processes and events that led to the formation of Earth and life, as we know it.

Comets and asteroids may have delivered some of the water and other ingredients that allowed the complex chemistry of life to begin on Earth. For example, the amino acid glycine was discovered in the comet dust returned to Earth by the Stardust mission. Glycine is used by living organisms to make proteins. The discovery supports the theory that some of life's ingredients formed in space and were delivered to Earth long ago by meteorite and comet impacts.

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