What is an Asteroid?
The small bodies orbiting around the sun with a diameter less than 1000km or 600 miles are known as Asteroids. The asteroids are also known as minor planets or planetoids. Most of the asteroids are orbiting around the sun between Mars and Jupiter and form a flat ring surface called the asteroid belt. Many asteroids in the universe look similar to the planets but they are in relatively large groups and smaller in size. So, scientists kept them as individual objects and kept them under the terms of minor plants based on their physical properties. The major differences between asteroids and meteoroids are their size. The asteroid size is larger than he size of meteoroids.
This article describes the origin, classifications of asteroids, major milestones in asteroid research with size and facts of asteroids are explained in detail.
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Origin of Asteroids
According to the dynamical model, the asteroids in the universe are formed during the first million years after the formation of the solar system with the gravitational interaction among the giant planets, especially between Jupiter, Saturn, Uranus, and Neptune. The asteroids in the universe initially started moving towards the sun and then moved outwards away from the sun. Meanwhile, the asteroid belts evolved because of the collision among asteroids. The evidence for a collision of asteroids is found in the dynamical asteroid families. Due to the collision of asteroids, the asteroids became smaller than 40 km and sometimes, they get diverted from their orbits due to solar radiation.
Major Milestones in Asteroid Research and Asteroids Facts
On 1st January 1804, the astronomer Giuseppe Piazzi at Palermo from Italy was the first person to discover the asteroids. Initially, Piazzi discovered a comet and later he studied the object in the orbital elements. According to him, asteroids are found between the orbits of Mars and Jupiter. These planets-like objects are moving in the orbit between Mars and Jupiter. But he could not continue his research on asteroids after the 11th of February 1804. He also attracted the observation of a few astronomers, by publishing their reports in the press. But some astronomers did not believe his research.
In 1801, the German mathematician Carl Friedrich Gauss made a few observations on the methods for computing the orbit of minor planets. Later, German Hungarian astronomer, Franz von Zach kept Gauss’s predictions and rediscovered the objective of Piazzi in late 1801’s. They named the object Ceres, which is the name of the ancient Roman grain goddess and patron goddess of Sicily.
In the next six years, astronomers found three more faint objects that are similar to early asteroids namely Pallas, Juno and Vesta and found that the asteroids are the broken pieces of the exploded planets. In 1845, Karl L. Hencke renewed the research of flurry and discovered a fifth asteroid also named Astraea.
As of 1866, Astronomers found 88 asteroids. An American astronomer, Daniel Kirkwood researched the distribution of asteroids and their distance separation from the sun. In 1891, astronomers introduced photography for making research on new asteroids and identified about 322 asteroids. At the end of the 19th century, they found about 464 asteroids and it reached up to 108,066 at the end of the 20th century. During the 21st century, it reached above 1,000,000. In the research, they found that more than 90 percent of the asteroids were less than one kilometre. These orbits can also cross the orbit of earth and also have the potential to collide with the planets. As of 2020, astronomers have found about 990,933 asteroids; in that, about 55 percent were named.
Geography of the Asteroid Belt
The geography of the asteroid belts is mainly described in their features. Asteroids are mainly coordinated with the latitude, longitude, and altitude for finding their exact location in the universe. Similarly, any objects in the solar system can be identified with the three parameters namely, heliocentric ecliptic longitude, heliocentric ecliptic latitude, and heliocentric distance. But the positions found through this method will be valid for certain periods of time because all the objects in the universe are moving continuously. The path of the object in the solar system is called orbit, with which the object will revolve around the sun.
All the asteroids in the universe move around the sun in elliptical orbits as in the direction of the major planets. Some elliptical orbits look like circles or eccentric. It is possible to predict the past and future location of the asteroids by finding their orbit. The orbits are mainly used to describe the geographic location of the asteroid belt.
Classification of Asteroids
Based on the composition, the asteroids are mainly classified into three types. They are listed below.
The most common type of asteroid is C-type (chondrite) asteroids. The main composition of C-type asteroids is clay and silicate rocks. These are the most ancient objects in the solar system and look dark in colour.
The stony asteroids or S-type asteroids are made up of silicate materials and nickel-iron.
The metallic or M-type asteroids are mainly made of nickel-iron. They are located far away from the sun and some of these asteroids may experience high temperatures even after partial melting. These asteroids have iron sinking to the centre and forcing basaltic (volcanic) lava to the surface.
Asteroids are also classified into three types based on their geographical location. They are listed below.
Main Asteroid Belt
Most of the asteroids are orbiting around the sun between Mars and Jupiter within the asteroid belt. This main asteroid belt contains about 1.1 to 1.9 million asteroids, whose asteroid size is more than 1-kilometre diameter. The asteroid belt also contains millions of smaller asteroids. The asteroids in the main asteroid belt do not have very elongated orbits. During the origin of the solar system, these asteroids formed a new gravitational field between Jupiter and created the planetary bodies in this region. Also, the small bodies collide with one another and are fragmented to form asteroids.
Trojans
The asteroids which share their orbits with larger planets but do not collide with planets are known as Trojan asteroids. Because the asteroids and planets are placed in different places in orbit. This is called the L4 and L5 Lagrangian points. Here, the gravitational force among the planets in the orbit and the sun balances the trojans. Or else, the trojans may fly out of orbits. The population of Trojan asteroids is more in Jupiter. The Trojan asteroids are found between the orbits of Mars, Neptune. In 2011, astronomers from NASA discovered the Earth trojan.
Near-Earth Asteroids
The asteroids, whose orbits are closely passed through the orbit of the earth are known as Near earth asteroids. The asteroids, which actually cross the earth’s orbital, are known as Earth-crossers.
This article described the origin of asteroids, the classification of asteroids, the size and facts of asteroids with the geography of the asteroid belts.
FAQs on Asteroids
1. What exactly is an asteroid?
An asteroid is a small, rocky, and airless celestial body that orbits the Sun. Often called minor planets or planetoids, they are much smaller than planets. Most asteroids in our solar system are found in a region known as the main asteroid belt, located between the orbits of Mars and Jupiter.
2. What are the main types of asteroids based on their composition?
Based on their composition, asteroids are primarily classified into three main types:
- C-type (chondrite): These are the most common type, making up about 75% of known asteroids. They are composed of clay and silicate rocks, are dark in appearance, and are among the most ancient objects in the solar system.
- S-type (stony): These asteroids are made of silicate materials and nickel-iron. They are found mostly in the inner asteroid belt.
- M-type (metallic): These are primarily made of nickel-iron. They are thought to be the remnants of the metallic cores of larger, ancient bodies that were shattered by collisions.
3. What is the main asteroid belt and where is it located?
The main asteroid belt is a vast, ring-shaped region in our solar system situated between the orbits of Mars and Jupiter. It contains millions of asteroids of various sizes, from tiny pebbles to large bodies hundreds of kilometres in diameter. It is believed that the strong gravitational influence of Jupiter prevented the material in this region from coalescing into a single planet.
4. How are asteroids different from comets?
While both are small bodies orbiting the Sun, asteroids and comets have key differences. Asteroids are primarily made of rock and metal and formed closer to the Sun where it was too warm for ices to remain solid. In contrast, comets are composed of ice, dust, and rock. When a comet's orbit brings it close to the Sun, the ice vaporises, creating a glowing cloud called a coma and a visible tail, which asteroids do not have.
5. How large can asteroids be?
The size of asteroids varies enormously. The largest known asteroid, Ceres, has a diameter of about 940 kilometres and is also classified as a dwarf planet. Other large asteroids include Vesta (about 525 km) and Pallas (about 512 km). However, the vast majority of asteroids are much smaller, many being less than a kilometre across.
6. Why do some asteroids leave their orbit?
An asteroid's orbit can be disturbed for several reasons. The most significant factor is the immense gravitational pull from large planets, especially Jupiter. This gravitational influence can nudge an asteroid, altering its path and sometimes sending it into a new orbit that might cross the paths of other planets. Additionally, collisions between asteroids can shatter them and send the fragments into entirely different trajectories.
7. What are Near-Earth Asteroids (NEAs)?
Near-Earth Asteroids, or NEAs, are asteroids whose orbits bring them into Earth's neighbourhood, specifically within 1.3 astronomical units of the Sun. While most pose no threat, a subset known as Potentially Hazardous Asteroids (PHAs) are closely monitored by space agencies like NASA. These monitoring programs track their orbits to assess any potential future impact risk to our planet.
8. Why is it important for scientists to study asteroids?
Studying asteroids provides crucial insights into our solar system. Key reasons for their importance include:
- Understanding Solar System Formation: Asteroids are pristine remnants from the early solar system, offering clues about the conditions and materials present when the planets formed 4.6 billion years ago.
- Planetary Defence: By identifying and tracking asteroids, particularly NEAs, scientists can predict and potentially mitigate future impact threats to Earth.
- Future Resources: Asteroids are rich in minerals and water, which could potentially be mined for future space missions or use on Earth.
9. How many asteroids have been discovered?
As of the early 2020s, astronomers have discovered and catalogued over one million asteroids. This number is constantly growing as telescopes and survey technologies become more powerful and efficient at detecting these small, faint objects. The actual number of asteroids in our solar system is estimated to be many millions more, most of which are too small to be detected from Earth.
10. Besides the main belt, where else can asteroids be found?
While the majority of asteroids reside in the main belt, they can also be found in other locations. A significant population, known as Trojan asteroids, share an orbit with a larger planet but do not collide with it because they are situated in stable gravitational points (Lagrangian points) ahead of and behind the planet. Jupiter has the largest population of Trojans, but they have also been found orbiting with Neptune, Mars, and even Earth.
