The Small Stuff Matters

The solar system's smallest objects carry its biggest clues:

• They are leftover building blocks from the solar system's formation 4.6 billion years ago
• Their ice and minerals record the chemistry of the early Sun's surroundings
• Comets that strike a planet can deliver water and organic molecules, as may have happened on early Earth
• Tracking near-Earth objects today is the first step toward deflecting a future impactor

The Oort Cloud, at the far edge of this collection, extends nearly a light-year from the Sun and may hold trillions of icy bodies — a frozen archive of where everything began.