The asteroid belt of our solar system



Artist’s illustration of the asteroid belt of our solar system. Credit: NASA / McREL

Asteroids, sometimes referred to as minor planets, are rocky remnants of the initial formation of our solar system about 4.6 billion years ago. The number of currently known asteroids is over a million!

Most of this ancient space rubble can be found orbiting our Sun between ">March and Jupiter in the main asteroid belt. Asteroids vary in size from Vesta – the largest with a diameter of around 329 miles (530 kilometers) – to bodies less than 10 meters in diameter. The total mass of all asteroids combined is less than that of the Moon.

Most asteroids are irregular in shape, although a few are almost spherical, and they are often pitted or cratered. As they revolve around the Sun in elliptical orbits, asteroids also spin, sometimes quite erratically, tumbling as they go. Over 150 asteroids are known to have a small companion moon (some have two moons). There are also binary (double) asteroids, in which two rocky bodies of roughly equal size orbit each other, as well as a triple asteroid system.


The three major compositional classes of asteroids are types C, S and M.

  • Type C asteroids (chondrites) are the most common. They are probably made up of clayey and silicate rocks and are dark in appearance. They are among the oldest objects in the solar system.
  • S (“stony”) types are made of silicate materials and nickel-iron.
  • M types are metallic (nickel-iron). The differences in composition of asteroids are related to the distance at which they formed from the Sun. Some experienced high temperatures after their formation and partial melting, with iron sinking into the center and forcing basaltic (volcanic) lava to the surface.

Asteroid orbits can be altered by Jupiter’s massive gravity – and by occasional close encounters with Mars or other objects. These encounters can force asteroids out of the main belt and send them into space in all directions through the orbits of other planets. Stray asteroids and asteroid fragments have crashed into Earth and other planets in the past, playing a major role in altering the geological history of the planets and in the evolution of life on Earth.

Scientists continuously monitor the asteroids passing through Earth, whose trajectories intersect Earth’s orbit, and near-Earth asteroids that approach Earth’s orbital distance of about 45 million kilometers (28 million miles). and may present an impact hazard. Radar is a valuable tool for detecting and monitoring potential impact hazards. By reflecting the transmitted signals on objects, images and other information can be derived from the echoes. Scientists can learn a lot about an asteroid’s orbit, rotation, size, shape, and metal concentration.

Classifications of asteroids

Main asteroid belt: The majority of known asteroids orbit the asteroid belt between Mars and Jupiter, generally with slightly elongated orbits. The belt is estimated to contain between 1.1 and 1.9 million asteroids over 1 kilometer (0.6 mile) in diameter, and millions of smaller asteroids. Early in the history of the solar system, the gravity of the newly formed Jupiter ended the formation of planetary bodies in this region and caused the small bodies to collide with each other, fragmenting them into the asteroids we see today. ‘hui.

Trojans: These asteroids share an orbit with a larger planet, but do not collide with it as they congregate around two particular places in the orbit (called Lagrange points L4 and L5). There, the gravitational pull of the Sun and the planet is balanced by the tendency of a Trojan horse to fly out of its orbit. The Jupiter Trojans form the largest population of Trojan asteroids. They are believed to be as numerous as the asteroids in the asteroid belt. There is Mars and Neptune Trojans and ">Nasa announced the discovery of a terrestrial Trojan horse in 2011.

Near-Earth asteroids: These objects have orbits that pass close to that of the Earth. Asteroids that actually cross Earth’s orbital path are called Earth-crossers.

How asteroids get their names

The International Astronomical Union Committee on Small Body Nomenclature is not very strict when it comes to naming asteroids. As a result, orbiting the Sun, we have a giant space rock named in honor of Mr. Spock – a cat named after the celebrity character “Star Trek”. There is also a space rock named in honor of the late rock musician Frank Zappa. There are also darker tributes, like the seven asteroids named for the Space Shuttle Columbia crew killed in 2003.

Asteroids are also named for places and a variety of other things. (The IAU advises against naming asteroids for pets, so Mr. Spock is on his own).

Asteroids are also assigned a number, for example (99942) Apophis. The Harvard Smithsonian Center for Astrophysics maintains a fairly up-to-date list of asteroid names.


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