Asteroids: The Rocky Remnants

Asteroids are small, rocky objects that orbit the Sun. They are often called minor planets or planetoids, and are remnants from the early formation of our solar system about 4.6 billion years ago.

Most asteroids are found in the asteroid belt between Mars and Jupiter, but they can be located throughout the solar system. They range in size from Vesta—the largest at about 329 miles (530 kilometers) in diameter—to bodies that are less than 33 feet (10 meters) across.

Despite there being millions of asteroids, the total mass of all asteroids combined is less than that of Earth's Moon. This makes them fascinating objects of study, as they represent preserved material from the solar system's infancy.

Asteroids are leftover building blocks from the early solar system. They formed from the solar nebula—the cloud of gas and dust that collapsed to form our Sun and planets about 4.6 billion years ago.

As dust particles collided and stuck together, they formed larger bodies called planetesimals. Most of these planetesimals eventually merged to form planets, but in the asteroid belt between Mars and Jupiter, Jupiter's strong gravity prevented them from coalescing into a planet.

This is why asteroids are often called "fossils" of the solar system—they preserve information about the conditions and materials present during the formation of our planetary system.

Asteroids are classified into different types based on their composition, which we determine by studying their reflectance spectra and sometimes by analyzing meteorites that have fallen to Earth.

The three main types are C-type (carbonaceous), S-type (silicaceous), and M-type (metallic). Each type represents different materials from the early solar system and formed at different distances from the Sun.

Understanding asteroid composition helps scientists piece together the history of our solar system and provides insights into the materials that were available during planet formation.

While most asteroids reside in the main asteroid belt between Mars and Jupiter, they can be found in several distinct groups throughout the solar system based on their orbits.

The main groups include the Main Asteroid Belt, Near-Earth Asteroids (NEAs), Trojan asteroids (which share orbits with planets), and asteroids in the Kuiper Belt beyond Neptune.

Understanding where asteroids are located helps scientists track potentially hazardous objects and plan future space missions to study these ancient solar system remnants.

Spacecraft missions to asteroids have revolutionized our understanding of these primitive bodies. By visiting asteroids directly, we can study their composition, structure, and history in ways impossible from Earth.

Notable missions include NASA's OSIRIS-REx, which collected samples from asteroid Bennu; Japan's Hayabusa2, which returned samples from Ryugu; and NASA's Dawn mission, which orbited Vesta and Ceres in the asteroid belt.

These missions not only advance our scientific knowledge but also help develop technologies for future asteroid mining and planetary defense against potential Earth-impacting asteroids.