By Doug Bennett Updated Mar 24, 2022
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The solar system contains a wide variety of objects besides the familiar planets. These objects range in size, composition and behavior. They can collide with Earth, producing consequences from fleeting shooting stars to potentially catastrophic impacts. These celestial bodies—comets, meteors, and asteroids—offer clues to our planet’s past and future.
Comets are dirty snowballs composed of rocks, dust, and frozen gases. When they near the Sun, surface ice melts, releasing gas that the solar wind stretches into the iconic cometary tail. Short‑period comets, with orbits under 200 years, are relics of the early Solar System and originate in the Kuiper Belt beyond Neptune. Long‑period comets, hailing from the distant Oort Cloud, can take up to 30 million years to complete a single orbit.
Meteors, commonly called shooting stars, are small fragments of rock and debris that burn up as they plunge through Earth’s atmosphere. Most are pea‑sized or smaller and disintegrate before reaching the surface. Occasionally, larger bodies survive the atmospheric passage and become meteorites. NASA estimates that 1,000 to 10,000 tons of meteoritic material enter the atmosphere each day.
Asteroids, or minor planets, are sizable rocky bodies without atmospheres that orbit the Sun yet fall short of planetary status. The main asteroid belt between Mars and Jupiter hosts millions of objects ranging from less than 0.5 mi to nearly 600 mi in diameter. More than 150 asteroids carry tiny moons. Gravitational interactions with Jupiter, Mars, and neighboring bodies can nudge asteroids from the belt, sending them onto Earth‑crossing trajectories.
Comet impacts are theorised to have delivered Earth’s water and the building blocks of life. The largest meteorite recovered, weighing nearly 120,000 lbs, was found in southwest Africa. About 65 million years ago, an asteroid impact created a crater over 100 mi wide in the Yucatán Peninsula, widely linked to the dinosaur extinction. In the United States, the Chesapeake Bay crater—56 mi across—was formed by an asteroid roughly 36 million years ago. NASA reports 1,238 known potentially hazardous asteroids (PHAs), defined as bodies over 500 ft that pass within 4.6 million mi of Earth.
