-Asteroids-

classification, locations in the solar system, origin

Asteroids or small planets are hard rock objects of various sizes that formed in the beginning of the solar system. Although the number of these objects is measured in millions, their total mass is less than the mass of the Moon.


Asteroids are thought to be remnants of the planetary process that took place about 4.5 billion years ago. The dust and frozen gases in the solar nebula clumped together to form larger and smaller blocks of rock, which continued to unite and result in the formation of planetary embryos. Not everyone was destined to become a full-fledged planet. Some of them split into larger and smaller pieces in mutual collisions. Some asteroids no longer had enough mass for further growth and their size did not increase.


At the beginning of the solar system, the big planets changed their location. Jupiter and Saturn moved closer to the Sun, then away from it. The massive movement of the masses caused changes in the orbits of asteroids and comets, and many of these objects fell in the direction of the Sun, colliding with the newly formed Earth and other solid planets on their way. It is possible, that during this late bombing comets and asteroids carried water and organic matter to Earth.


Asteroids range in size from several hundred kilometers to a few meters. Most are irregularly shaped objects, the surfaces of which are covered with dust and craters of various sizes, which indicate regular collisions. They have no atmosphere and the temperature on their surface is about -75 degrees Celsius.


Asteroids orbit the Sun and rotate around their axis. At least 150 asteroids with one or more natural satellites are currently known. Two and three asteroid systems have also been discovered, where asteroids of the same size rotate around a common center of mass.


Most asteroids are located between the orbits of Jupiter and Mars. This cluster is called the main asteroid belt. It contains more than 200 asteroids with a diameter of more than 100 kilometers. The largest asteroids are called planetoids. Those larger than 1 kilometer could be in the asteroid belt from 1-2 million. The largest asteroid in the area is Vesta (530 km), which is surpassed by the dwarf planet Ceres, which also orbits in the main asteroid belt.


Ceres was the first object discovered in the main asteroid belt to be spotted in 1801 by the Italian priest and astronomer Giuseppe Piazzi. At the beginning of the 19th century, a number of new asteroids were discovered, originally granted planetary status. In 1802, William Herschel introduced the term asteroid, which means “star-like”. In 1851, 15 asteroids were already known and the newly discovered objects were given not only a name but also a serial number. This numbering order is still followed today.


Some asteroids orbit the Sun with a planet in the same orbit without colliding with it. These are the trojans that inhabit the so-called Lagrange points (specifically in points L4 and L5), where the gravitational forces of the planet and the Sun are balanced. Jupiter has the largest number of trojans, but such asteroids have also been discovered for Mars, Neptune, Uranus, Venus and Earth.



The population of asteroids close to Earth is especially noteworthy. Their orbits are relatively close to or even cross the Earth’s orbit. This group of asteroids is under special surveillance, and much attention is being paid to the search for new asteroids, as there is a possibility that someone may collide with the Earth, causing a catastrophe of a smaller or larger scale. More than 10,000 asteroids close to Earth are currently known, of which about 1,000 are potentially dangerous.


Depending on their composition, asteroids are divided into three main groups:

  • C-type or carbonaceous asteroids (chondrites), which are the most common (approximately 75% of known asteroids). They consist of carbon and various hard rocks and inhabit the further regions of the main asteroid belt. Type C asteroids have a dark gray tinge;
  • S-type or silicon asteroids make up about 17% of all known asteroids. They contain various silicon compounds, as well as nickel and iron. These reddish and greenish asteroids inhabit the area of the main asteroid belt.
  • M-type or metallic asteroids are mostly reddish and are located in the middle of the main asteroid belt. Their basic constituents are various metals, mainly iron and nickel.


In addition to the compounds already mentioned, asteroids also contain water, but in smaller amounts than comets. Research has shown that there are a variety of organic substances on asteroids, including amino acids.


Asteroids regularly collide with the Earth, causing larger and smaller scale disasters. The last of the largest to attract the world’s attention took place on the morning of February 15, 2013, when an asteroid of about 18-20 meters entered the Earth’s atmosphere and exploded at a height of about 15-25 kilometers. The shockwave shattered windows in the nearby city of Chelyabinsk, Russia, injuring more than 1,500 people.


In order to draw attention to asteroids and their potential threats to the Earth’s inhabitants, the United Nations (UN) in 2018 declared June 30 as the International Asteroid Day, as part of which events in Latvia are organized by the project Meteoriti.LV.


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