Asteroids and Asteroid Belt

Asteroids are relatively small, primarily rocky or metallic chunks of matter that orbit the Sun. They are like planets, but much smaller; the largest asteroid, Ceres, is only about 930 kilometers across, and only ten asteroids larger than 250 kilometers across are known to exist in the solar system. While most asteroids are made mostly of carbon-rich rock, some are made at least partially of iron and nickel.

Aside from the largest ones, asteroids tend to be irregular in shape, rotating and tumbling as they move through the solar system.

The four largest asteroids are the dwarf planet Ceres, Pallas, Vesta, and Hygiea. Other well-known asteroids include Eros, Gaspra, Ida, and Dactyl.

Asteroid belt

The asteroid belt (or the “main belt”) is the region between the orbit of Mars and the orbit of Jupiter—about 240 to 800 million kilometers away from the Sun.

The vast majority of known asteroids orbit in this belt. The main belt itself is divided into thinner belts, separated by object-free zones called Kirkwood Gaps. The gaps are named after the American astronomer Daniel Kirkwood, who first discovered them.

Even though there are at least a million or more asteroids in the main belt, the typical distance between asteroids is huge—thousands or even millions of miles.

Asteroids located other than Asteroid Belt

There are many asteroids in other regions of the solar system. Chiron, for example, which was discovered in 1977, orbits between Saturn and Uranus.

Another example is the Trojan asteroids that follow the orbit of Jupiter near Lagrange points—one group preceding the planet, the other following it—and can thus orbit safely without crashing into Jupiter itself.

2010TK7 : Earth’s Trojan Satellite

It was discovered in 2010 that Earth is not alone in its orbit around the Sun. There is a small ‘Trojan’ asteroid 2010TK7  that sits in front of earth and leads it. This is the 1st Trojan Asteroid of Earth discovered using the WISE Telescope. It has now become the First known Trojan Asteroid in Earth’s Orbit.

A Trojan asteroid shares an orbit with a larger planet or moon, but does not collide. So a Trojan has a particular position in a stable spot – either in front of a planet or behind it called Lagrangian points. Because the asteroid and planet are constantly on the same orbit, they can never collide. Trojan asteroids were anticipated in earth’s orbit but never discovered yet.  Nasa discovered the asteroid, which lies 80 million km from Earth, using its Widefield Infrared Survey Explorer (WISE) telescope. Astronomers have long thought that Earth did have Trojans but their discovery has proved elusive because they can’t be seen in daylight.

Origin of Asteroids

The origin of asteroids remains the subject of scientific study. Astronomers today think that most asteroids are planetesimals that never quite combined with other bodies to form planets.

Some asteroids, on the other hand, may be the shattered remains of planets or protoplanets that suffered huge collisions and broke into pieces.

Number of Asteroids

Many thousands of asteroids are being tracked regularly, and tens of thousands have been identified and catalogued. At least one million asteroids are estimated to exist; of those, astronomers estimate that about one in ten can be observed from Earth.